satellite, artificial

satellite, artificial, object constructed by humans and placed in orbit around the earth or other celestial body (see also space probe). The satellite is lifted from the earth's surface by a rocket and, once placed in orbit, maintains its motion without further rocket propulsion. The first artificial satellite, Sputnik I, was launched on Oct. 4, 1957, by the USSR; a test payload of a radio beacon and a thermometer demonstrated the feasibility of orbiting a satellite. The first U.S. satellite, Explorer I, launched on Jan. 31, 1958, returned data that was instrumental in the discovery of the Van Allen radiation belts. During the first decade of space exploration, all of the satellites were launched from either the United States or USSR. Today, there are more than three dozen launch sites in use or under construction in more than a dozen countries

Satellite Orbits

If placed in an orbit high enough to escape the frictional effects of the earth's atmosphere, the motion of the satellite is controlled by the same laws of celestial mechanics that govern the motions of natural satellites, and it will remain in orbit indefinitely. At heights less than 200 mi (320 km) the drag produced by the atmosphere will slow the satellite down, causing it to descend into the denser portion of the atmosphere where it will burn up like a meteor. To attain orbital altitude and velocity, multistage rockets are used, with each stage falling away as its fuel is exhausted; the effect of reducing the total mass of the rocket while maintaining its thrust is to increase its speed, thus allowing it to achieve the required velocity of 5 mi per sec (8 km per sec). At this speed the rocket's forward momentum exactly balances its downward gravitational acceleration, resulting in orbit. Once above the lower atmosphere, the rocket bends to a nearly horizontal flight path, until it reaches the orbital height desired for the satellite.

Unless corrections are made, orbits are usually elliptical; perigee is the point on the orbit closest to the earth, and apogee is the point farthest from the earth. Besides this eccentricity an orbit of a satellite about the earth is characterized by its plane with respect to the earth. An equatorial orbit lies in the plane of the earth's orbit. A polar orbit lies in the plane passing through both the north and south poles. A satellite's period (the time to complete one revolution around the earth) is determined by its height above the earth; the higher the satellite, the longer the period. At a height of 200 mi (320 km), the period of a circular orbit is 90 min; at 500 mi (800 km), it increases to 100 min. At a height of 22,300 mi (36,000 km), a satellite has a period of exactly 24 hr, the time it takes the earth to rotate once on its axis; such an orbit is called geosynchronous. If the orbit is also equatorial, the satellite will remain stationary over one point on the earth's surface.

Tracking and Telemetry

Since more than 1,000 satellites are presently in orbit, identifying and maintaining contact requires precise tracking methods. Optical and radar tracking are most valuable during the launch; radio tracking is used once the satellite has achieved a stable orbit. Optical tracking uses special cameras to follow satellites illuminated either by the sun or laser beams. Radar tracking directs a pulse of microwaves at the satellite, and the reflected echo identifies both its direction and distance. Nearly all satellites carry radio transmitters that broadcast their positions to tracking antennas on the earth. In addition, the transmitters are used for telemetry, the relaying of information from the scientific instruments aboard the satellite.

Types of Satellites

Satellites can be divided into five principal types: research, communications, weather, navigational, and applications.

Research satellites measure fundamental properties of outer space, e.g., magnetic fields, the flux of cosmic rays and micrometeorites, and properties of celestial objects that are difficult or impossible to observe from the earth. Early research satellites included a series of orbiting observatories designed to study radiation from the sun, light and radio emissions from distant stars, and the earth's atmosphere. Notable research satellites have included the Hubble Space Telescope, the Compton Gamma-Ray Observatory, the Chandra X-ray Observatory, the Infrared Space Observatory, and the Solar and Heliospheric Observatory (see observatory, orbiting). Also contributing to scientific research were the experiments conducted by the astronauts and cosmonauts aboard the space stations launched by the United States (Skylab) and the Soviet Union (Salyut and Mir); in these stations researchers worked for months at a time on scientific or technical projects. The International Space Station, currently under construction, will continue this work.

Communications satellites

provide a worldwide linkup of radio, telephone, and television. The first communications satellite was Echo 1; launched in 1960, it was a large metallized balloon that reflected radio signals striking it. This passive mode of operation quickly gave way to the active or repeater mode, in which complex electronic equipment aboard the satellite receives a signal from the earth, amplifies it, and transmits it to another point on the earth. Relay 1 and Telstar 1, both launched in 1962, were the first active communications satellites; Telstar 1 relayed the first live television broadcast across the Atlantic Ocean. However, satellites in the Relay and Telstar program were not in geosynchronous orbits, which is the secret to continuous communications networks. Syncom 3, launched in 1964, was the first stationary earth satellite. It was used to telecast the 1964 Olympic Games in Tokyo to the United States, the first television program to cross the Pacific Ocean. In principle, three geosynchronous satellites located symmetrically in the plane of the earth's equator can provide complete coverage of the earth's surface. In practice, many more are used in order to increase the system's message-handling capacity. The first commercial geosynchronous satellite, Intelsat 1 (better known as Early Bird), was launched by COMSAT in 1965. A network of 29 Intelsat satellites in geosynchronous orbit now provides instantaneous communications throughout the world. In addition, numerous communications satellites have been orbited by commercial organizations and individual nations for a variety of telecommunications tasks.

communications satellite artificial satellite that functions as part of a global radio-communications network. Echo 1, the first communications satellite, launched in 1960, was an instrumented inflatable sphere that passively reflected radio signals back to earth. Later satellites carried with them electronic devices for receiving, amplifying, and rebroadcasting signals to earth. Relay 1, launched in 1962 by the National Aeronautics and Space Administration (NASA), was the basis for Telstar 1, a commercially sponsored experimental satellite. Geosynchronous orbits (in which the satellite remains over a single spot on the earth's surface) were first used by NASA's Syncom series and Early Bird (later renamed Intelsat 1), the world's first commercial communications satellite.

In 1962, the U.S. Congress passed the Communications Satellite Act, which created the Communications Satellite Corporation (Comsat). Agencies from 17 other countries joined Comsat in 1964 in forming the International Telecommunications Satellite Consortium (Intelsat) for the purpose of establishing a global commercial communications network. Renamed the International Telecommunications Satellite Organization in 1974 and a private corporation since 2001, Intelsat now has a network of 28 satellites in geosynchronous orbits that provides instantaneous communications throughout the world. It has orbited several series of Intelsat satellites, beginning with Intelsat 1 (Early Bird) in 1965.

Inmarsat was established in 1979 to serve the maritime industry by developing satellite communications for ship management and distress and safety applications. Inmarsat was originally an intergovernmental organization called the International Maritime Satellite Organization but later changed its name to the International Mobile Satellite Organization to reflect its expansion into land, mobile, and aeronautical communications. In 1999 it became a private company as Inmarsat, and the International Mobile Satellite Organization became responsible for overseeing Inmarsat's public service obligations. Inmarsat's users now include thousands of people who live or work in remote areas without reliable terrestrial networks. Inmarsat presently has ten satellites in geosynchronous orbits.

In addition to the Intelsat and Inmarsat satellites, many others are in orbit, some managed by private companies and others by government-owned operators. These are used by individual countries, organizations, and commercial ventures for internal communications or for business or military use. A new generation of satellites, called direct-broadcast satellites, transmits directly to small domestic antennas to provide such services as cablelike television programming.

Weather satellites

Weather satellites, or meteorological satellites, provide continuous, up-to-date information about large-scale atmospheric conditions such as cloud cover and temperature profiles. Tiros 1, the first such satellite, was launched in 1960; it transmitted infrared television pictures of the earth's cloud cover and was able to detect the development of hurricanes and to chart their paths. The Tiros series was followed by the Nimbus series, which carried six cameras for more detailed scanning, and the Itos series, which was able to transmit night photographs. Other weather satellites include the Geostationary Operational Environmental Satellites (GOES), which send weather data and pictures that cover a section of the United States; China, Japan, India, and the European Space Agency have orbited similar craft. Current weather satellites can transmit visible or infrared photos, focus on a narrow or wide area, and maneuver in space to obtain maximum coverage.

weather satellite, artificial satellite used to gather data on a global basis for improvement of weather forecasting. Information includes cloud cover, storm location, temperature, and heat balance in the earth's atmosphere. The first weather satellites in the United States were those of the Tiros series, which began in 1960; the Nimbus series, which moved in a polar orbit, was next; the Environmental Science Services Administration (ESSA) started in 1966 and launched weather satellites; and in 1972, the Earth Resources Technology Satellite (ERTS) provided photographs to help forecasting. Other meteorological satellites include a series of Geostationary Operational Environmental Satellites (GOES), which send weather data and pictures that cover a section of the United States; China, Japan, India, and the European Space Agency (ESA) have similar craft. The National Oceanic and Atmospheric Administration's satellite series relay meteorological data to stations on the surface, including information on possible changes in various weather parameters that may signal climate change.

Navigation satellites

Navigation satellites were developed primarily to satisfy the need for a navigation system that nuclear submarines could use to update their inertial navigation system. This led the U.S. navy to establish the Transit program in 1958; the system was declared operational in 1962 after the launch of Transit 5A. Transit satellites provided a constant signal by which aircraft and ships could determine their positions with great accuracy. In 1967 civilians were able to enjoy the benefits of Transit technology. However, the Transit system had an inherent limitation. The combination of the small number of Transit satellites and their polar orbits meant there were some areas of the globe that were not continuously covered—as a result, the users had to wait until a satellite was properly positioned before they could obtain navigational information. The limitations of the Transit system spurred the next advance in satellite navigation: the availability of 24-hour worldwide positioning information. The Navigation Satellite for Time and Ranging/Global Positioning Satellite System (Navstar/GPS) consists of 24 satellites approximately 11,000 miles above the surface of the earth in six different orbital planes. The GPS has several advantages over the Transit system: It provides greater accuracy in a shorter time; users can obtain information 24 hours a day; and users are always in view of at least five satellites, which yields highly accurate location information (a direct readout of position accurate to within a few yards) including altitude. In addition, because of technological improvements, the GPS system has user equipment that is smaller and less complex. The former Soviet Union established a Navstar equivalent system known as the Global Orbiting Navigation Satellite System (GLONASS). The Russian-operated GLONASS will use the same number of satellites and orbits similar to those of Navstar when complete. Many of the handheld GPS receivers can also use the GLONASS data if equipped with the proper processing software.

Applications satellites are designed to test ways of improving satellite technology itself. Areas of concern include structure, instrumentation, controls, power supplies, and telemetry for future communications, meteorological, and navigation satellites.

Satellites also have been used for a number of military purposes, including infrared sensors that track missile launches; electronic sensors that eavesdrop on classified conversations; and optical and other sensors that aid military surveillance. Such reconnaissance satellites have subsequently proved to have civilian benefits, such as commercially available satellite photographs showing surface features and structures in great detail, and fire sensing in remote forested areas. The United States has launched several Landsat remote-imaging satellites to survey the earth's resources by means of special television cameras and radiometric scanners. Russia and other nations have also launched such satellites; the French SPOT satellite provides higher-resolution photographs of the earth.

navigation satellite, artificial satellite designed expressly to aid the navigation of sea and air traffic. Early navigation satellites, from the Transit series launched in 1960 to the U.S. navy's Navigation Satellite System, relied on the Doppler shift. Based on the shift in the satellite's frequency, a ship at sea could accurately determine its longitude and latitude. The Global Positioning System (GPS), which uses a web of 24 Navstar satellites in 12-hour orbits, employs the more accurate triangulation method to determine position. Each satellite broadcasts time and position messages continuously. Precise to within a few yards, the GPS can also be used for nonnavigation purposes, such as surveying, tracking migrating animals, and plotting the crop yields of small sections of farmland. The former Soviet Union established a Navstar-equivalent system known as the Global Orbiting Navigation Satellite System (GLONASS). Russia's GLONASS will use the same number of satellites and orbits similar to those of Navstar when complete.

Introduction to Global Satellite Systems

Several different types of global satellite communications systems are in various stages of development. Each system, either planned or existing, has a unique configuration optimized to support a unique business plan based on the services offered and the markets targeted.

In the last few years more than 60 global systems have been proposed to meet the growing demand for international communications services. More are being planned and these are in addition to a large number of new regional systems.

Some of the global systems intend to provide global phone service, filling in where ground-based wireless systems leave off or providing seamless connectivity between different systems. Others intend to provide global data connectivity, either for low-cost short message applications such as equipment monitoring, or for high-speed Internet access anywhere in the world.

The global phone systems will target two very different markets. The first is the international business user, who want the ability to use a single mobile wireless phone anywhere in the world. This is impossible today on terrestrial systems because mobile phone standards are different from region to region. The second market is unserved and underserved communities where mobile and even basic telecommunications services are unavailable.

Because global and regional satellite systems are relatively new in non-military communications, these market approaches still are untested and it is likely that economics, user acceptance rates, technical difficulties and other factors will cause adjustments in the business plans of many of these systems.

The Types of Satellite Systems

The design of a satellite system is closely tied to the market it is intended to serve and the type of communications services it is intended to offer. There are four general system designs, which are differentiated by the type of orbit in which the satellites operate: Geostationary Orbit (GEO), Low-earth Orbit, Medium-earth Orbit (MEO), and Highly Elliptical Orbit (HEO). Each of these has various strengths and weaknesses in its ability to provide particular communications services.

Outside of the well-defined GEO universe, the differences between these systems is often not absolute and the acronyms applied to a system can be confusing and sometimes misleading. Several systems, for example, are variously described as LEOs and MEOs. Constantly evolving technology along with newly developing markets and service definitions combine to blur the lines between one satellite system and another.

The definitions below are meant to describe the general characteristics of GEOs, MEOs, LEOs and HEOs. Although examples of commercial systems employing these satellites are given, keep in mind that each system has unique characteristics that may not match precisely the general descriptions. The same caution should be applied to ascribing a particular satellite type's limitations to any one commercial system, since each uses several strategies for minimizing or overcoming the limitations inherent in satellite designs. For example, some systems may employ more than one type of satellite.

GEOSTATIONARY (GEO)

GEO systems orbit the Earth at a fixed distance of 35,786 kilometers (22,300 miles). The satellite's speed at this altitude matches that of the Earth's rotation, thereby keeping the satellite stationary over a particular spot on the Earth. Examples of GEO systems include INTELSAT, Inmarsat, and PanAmSat.

Geostationary satellites orbit the Earth above the equator and cover one third of the Earth's surface at a time. The majority of communications satellites are GEOs and these systems will continue to provide the bulk of the communications satellite capacity for many years to come.

GEOs support voice, data, and video services, most often providing fixed services to a particular region. For example, GEO satellites provide back-up voice capacity for the majority of the U.S. long distance telephone companies and carry the bulk of nation-wide television broadcasts, which commonly are distributed via from a central point to affiliate stations throughout the country.

Until recently, the large antennae and power requirements for GEO systems limited their effectiveness for small-terminal and mobile services. However, newer high-powered GEO satellites using clusters of concentrated "spot beams" can operate with smaller terrestrial terminals than ever before and can support some mobile applications. GEO satellite coverage typically degrades beyond 20 degrees North Latitude and 20 degrees South Latitude.

GEO systems have a proven track record of reliability and operational predictability not yet possible for the more sophisticated orbital designs now being deployed. GEO systems are also less complicated to maintain because their fixed location in the sky requires relatively little tracking capability in ground equipment. In addition, their high orbital altitude allows GEOs to remain in orbit longer than systems operating closer to Earth. These characteristics, along with their high bandwidth capacity, may provide a cost advantage over other system types.

However, their more distant orbit also requires relatively large terrestrial antennae and high-powered equipment and are subject to transmission delays. In addition, since only a few large satellites carry the load for the entire system, a GEO satellite loss is somewhat more consequential than for the systems described below.

Summary of GEO Pros and Cons

* PRO: GEO systems have significantly greater available bandwidth than the LEO and MEO systems described below. This permits them to provide two-way data, voice and broadband services that may be unpractical for other types of systems.
* PRO: Because of their capacity and configuration, GEOs are often more cost-effective for carrying high-volume traffic, especially over long-term contract arrangements. For example, excess capacity on GEO systems often is reserved in the form of leased circuits for use as a backup to other communications methods.
* CON: GEO systems, like all other satellite systems, require line-of-sight communication paths between terrestrial antennae and the satellites. But, because GEO systems have fewer satellites and these are in a fixed location over the Earth, the opportunities for line of sight communication are fewer than for systems in which the satellites "travel" across the sky. This is a significant disadvantage of GEO systems as compared to LEO and MEO systems, especially for mobile applications and in urban areas where tall buildings and other structures may block line-of-sight communication for hand-held mobile terminals.
* CON: Some users have expressed concern with the transmission delays associated with GEO systems, particularly for high-speed data. However, sophisticated echo cancellation and other technologies have permitted GEOs to be used successfully for both voice and high-speed data applications.

LOW-EARTH ORBIT (LEO)

LEO systems fly about 1,000 kilometers above the Earth (between 400 miles and 1,600 miles) and, unlike GEOs, travel across the sky. A typical LEO satellite takes less than two hours to orbit the Earth, which means that a single satellite is "in view" of ground equipment for a only a few minutes. As a consequence, if a transmission takes more than the few minutes that any one satellite is in view, a LEO system must "hand off" between satellites in order to complete the transmission. In general, this can be accomplished by constantly relaying signals between the satellite and various ground stations, or by communicating between the satellites themselves using "inter-satellite links."

In addition, LEO systems are designed to have more than one satellite in view from any spot on Earth at any given time, minimizing the possibility that the network will loose the transmission. Because of the fast-flying satellites, LEO systems must incorporate sophisticated tracking and switching equipment to maintain consistent service coverage. The need for complex tracking schemes is minimized, but not obviated, in LEO systems designed to handle only short-burst transmissions.

The advantage of the LEO system is that the satellites' proximity to the ground enables them to transmit signals with no or very little delay, unlike GEO systems. In addition, because the signals to and from the satellites need to travel a relatively short distance, LEOs can operate with much smaller user equipment (e.g., antennae) than can systems using a higher orbit. In addition, a system of LEO satellites is designed to maximize the ability of ground equipment to "see" a satellite at any time, which can overcome the difficulties caused by obstructions such as trees and buildings.

There are two types of LEO systems, Big LEOs and Little LEOs, each describing the relative mass of the satellites used as well as their service characteristics.

Little LEO satellites are very small, often weighing no more than a human being, and use very little bandwidth for communications. Their size and bandwidth usage limits the amount of traffic the system can carry at any given time. However, such systems often employ mechanisms to maximize capacity, such as frequency reuse schemes and load delay tactics.

Little LEO systems support services that require short messaging and occasional low-bandwidth data transport, such as paging, fleet tracking and remote monitoring of stationary monitors for everything from tracking geoplatonic movements to checking on vending machine status. The low bandwidth usage may allow a LEO system to provide more cost effective service for occasional-use applications than systems that maximize their value based on bulk usage. Examples of Little LEO systems include Orbcomm, Final Analysis and Leo One.

Big LEO systems are designed to carry voice traffic as well as data. They are the technology behind "satellite phones" or "global mobile personal communications system" (GMPCS) services now being developed and launched.

Most Big LEO systems also will offer mobile data services and some system operators intend to offer semi-fixed voice and data services to areas that have little or no terrestrial telephony infrastructure. Smaller Big LEO constellations also are planned to serve limited regions of the globe. Examples of Big LEO systems include Iridium, Globalstar and the regional Constellation and ECO-8 systems.

An emerging third category of LEO systems is the so-called "super LEOs" or "mega LEOs," which will handle broadband data. The proposed Teledesic and Skybridge systems are examples of essentially Big LEO systems optimized for packet-switched data rather than voice. These systems share the same advantages and drawbacks of other LEOs and intend to operate with inter-satellite links to minimize transmission times and avoid dropped signals.

military satellites

Artificial satellites used for a variety of military purposes. Of approximately 4000 satellites successfully launched between 1957 and 1999, about 50% have been either specifically military or usable for military purposes. Major functions of military satellites include communications, positioning and navigation, meteorology, reconnaissance and surveillance, early warning, remote sensing, geodesy, and research.

Although only certain satellites are used continuously for military purposes, all communication satellites, including commercial, may find use during conflict. All contain the necessary equipment to transmit a signal over great distances to assist in the command, control, administration, and logistic support of military forces. Military communication satellites differ from commercial satellites only in that they contain specialized components, certain capabilities, and multiple redundant systems designed to make them less vulnerable and more effective in a hostile environment. See also Communications satellite.

Military forces must be able to quickly and precisely determine their position on the ground, in the air, or at sea. The Navstar Global Positioning System (GPS) is the most accurate and reliable satellite navigation system available. It includes 25 spacecraft in semisynchronous (12-h) orbits inclined at 55° to the Equator at 11,600 mi (18,700 km) altitude. Of these, 21 are operational and 4 are spares. The inclined orbits provide worldwide coverage, including the Poles. Russia also maintains global navigation satellite systems. Its Tsikada/Nadezhda low-Earth-orbit system functions similar to the United States' decommissioned Transit system. In addition, Russia operates the GLONASS navigation system. Similar to GPS, the system is less complex, but its satellites have proven less reliable than the United States' version. Receivers are available that will accept navigational data from either GPS or GLONASS. See also Satellite navigation systems.

From orbit, it is possible to obtain a wide-field-of-view image of the Earth, its cloud formations, and their movements. This meteorological information is valuable for military planning and operations.

The Television Infrared Observation Satellites (TIROS) have, for decades, traveled in Sun-synchronous, low Earth orbits providing images of cloud cover, snow, ice, and the sea surface. The Defense Meteorological Satellite Program (DMSP) consists of several satellites in low Earth, Sun-synchronous, polar orbits at an altitude of 517 mi (833 km), spaced to provide complete coverage of the Earth at various times of the day and night.

Russia operates the Meteor system of satellites. As many as five satellites are in low Earth orbit similar to TIROS with an orbital inclination of 81.2°. They image in the infrared spectrum. Several other countries maintain a meteorological satellite capability that provides useful information for military operations, although not specifically designed for military use. See also Meteorological satellites.

Military reconnaissance and surveillance satellites offer near-real-time unrestricted access over almost any area on Earth. Operating in many parts of the electromagnetic spectrum, they can be used to observe weapons development and deployment of forces, and to provide warning of attack by ground forces as well as targeting intelligence, technical intelligence on enemy capabilities, electronic intelligence, and bomb damage assessment.

Early warning satellites provide information on missile launch and nuclear detonation that give governments time to make strategic military decisions.

Remote-sensing satellites afford a unique view of Earth, providing vital information to military forces. The images produced by these satellites are used to conduct routine reconnaissance, analyze waterways, assist in exercise and strike planning, and provide up-to-date maps for forces deploying to unfamiliar areas. Important information is gathered not only in the visible spectrum but in other bands of the spectrum. See also Remote sensing.

Geodesy



Geodesy is the study of the Earth's size and shape. Geodetic data are important to the military in that the data affect position determination, navigation, map making, and a variety of other missions. Almost all satellites can be used for geodesy, provided their position in space can be accurately determined by optical or electronic means from the Earth.

In addition to the missions discussed above, there have been hundreds of military research and technology spacecraft, as well as thousands of experimental investigations for military purposes on space vehicles launched by all space-faring nations.

Satellite Antenna

Years of home brewing has taught me how to do and not to do a lot of things properly. This experience, along with reading AMSAT- NA, AMSAT-UK and ARRL publications (Note 1) has taught me how to build my projects better. Here are some tips I learned that may be of help with the most important part of an amateur radio satellite station, the antenna systems.
Low Cost Satellite Antennas

Materials to build satellite antennas can sometimes be found among junk most people would throw away. An old broken-off car radio antenna I found lying in the street became the vertical element of a two meter 5/8 wave groundplane for mode A and T. Four wire clothes hangers became the radials. Likewise all the remaining components were "salvaged" from other junk I had collected here and there. I used this simple matching network:
All you need to build a simple VHF or UHF 1/4 wave groundplane antenna is a coax chassis connector and number 12 or larger wire scraps. Solder the vertical element to the center conductor and attach the radials with nuts and bolts to the four corners, then solder each corner. Make the vertical element a bit longer than calculated and bend the radials down 25 to 30 degrees a short distance from the connector flange. Then trim the vertical element (in small increments) for the minimum SWR at the low end of the band in which it will be used. When the SWR begins to go back up, it should be lowest near the center of the band. If not, trim carefully until it is. Then little by little bend the radials down until you get a 1 to 1 SWR. This will be between 30 to 45 degrees, as shown below.


Number 8 wire was used. Ends were hammered flat, filed to shape and drilled. A small propane torch, used carefully so as not to overheat the connector, will make the soldering easy. Flux paste on the connector's flange will aid solder bonding. The vertical element's end was filed down until it fit inside the center pin connector. Waterproof the coax connector so water cannot seep into your coax.

Old weathered, corroded junked ham beams are another excellent source of recyclable antenna materials. I salvaged an old phased pair of inoperative Cushcraft two meter beams that were covered with corrosion and rust and were destined for the trash dump. Removing the rusted and corroded hardware was easy after a brisk wire brushing and soaking all the hardware with WD-40 (a penetrating oil) over night. After disassembling all the aluminum elements from the boom, I gave the boom and elements a good soaking and brushing in an acid bath. Acid solutions made specially for cleaning aluminum are available in well-stocked hardware stores. I now had clean looking elements and booms. A little time sanding out the corrosion pits with fine wet sandpaper and the elements and boom were as good as new.

I then drilled pilot holes on one boom 90 degrees and about an inch (2.5 cm) from the existing element holes. Upsizing the pilot holes to the diameter of the elements and securing all the elements with new sheet metal screws one size larger than the original size (so these new screws were tight in the old holes) tied them all together.


For the price of an acid bath and a few stainless steel nuts, bolts and sheet metal screws, a new two meter crossed yagi was born. Do not cut expenses with hardware. Always get stainless steel hardware for structural connections. Brass hardware can be used for electrical connections where there will not be much mechanical stress. The extra expense will be paid back with interest in a few years when it comes time for antenna maintenance.

Likewise I recycled a friend's junked ancient Hy-Gain trap tribander. After removing all the corroded and rusted hardware and traps and giving the elements a good acid bath, brushing and sanding, I had the makings (for free) for either a 15 or 10 meter beam for modes A, K or T. Essential rusted steel parts, like the boom to element brackets, were wire brushed and painted. As mode A was my objective, this beam came back to life as a full size three element 10 meter beam.

After years of trying various products and techniques to eliminate rust once it is well established, I have found a way that really works. First wire brush the metal with a wire brush wheel attached to either your bench grinder (the best way) or power drill until it is shiny. A base coat of Rust-Oleum (tm) Rusty Metal Primer (7769), then a coat of Clean Metal Primer (7773) and two coats of Aluminum Metallic Finish (7715) will keep your paint from blistering and the rust from reappearing for many years. Be sure to use Rust-Oleum thinner as needed to keep the paint at the proper viscosity so it brushes or sprays on properly.

Antenna wire left over from an 80 meter dipole project became the element for my 10 meter horizontal delta loop, which keeps my mode A downlink strong on the overhead portion of my mode A passes. By hanging it only 15 feet (4.5 meters) high with the feed-point near my shack's window I was able to feed it with a short scrap of coax left over from a 50 foot roll I bought for another antenna project. A quarter wave transformer section of 75 ohm RG-59/U coax from the delta loop's feed point to my 50 ohm coax feedline was an easy to make match (Note 2).

The 70cm Lindenblad antennas I described in AMSAT Journal and OSCAR News articles (Note 3) were built totally from scrap plastic and wire I already had. They were mounted on a pair of old broom handles that I knew I'd have a use for some day, as shown below. This is the best omnidirectional antenna I have ever used as the ability to switch polarizations minimizes QSB and maximizes signal strength.

Antenna Matching

I have had good luck with folded dipole driven elements as they are easy to design and match and have a "flatter" SWR curve than dipoles. The chart below shows the impedance step-up ratio for a two-conductor folded diple, as a function of conductor diameters and spacing. Dimensions d1, d2, and S are shown in the inset drawing. The formula for the step-up ratio, r, is also shown. Besides checking your SWR, check your power output from your matching network, as a bad matching network may give you a good SWR while dissipating RF as heat. I discovered an antenna feedpoint toroid balun that had a power loss I found unacceptable, so I replaced it with one of the lower loss balancing method discussed in the ARRL's Antenna Handbook (Note 2).

Circular polarized antennas capable of being switched from right to left handed circular polarization will give you the best performance, as polarization can change directions during a pass. The drawing below shows how to do this with 52 ohm antenna feed points. When calculating the length of individual cables be sure to include the velocity factor of the cables.

f you use folded dipole driven elements you can modify the design for a 400 ohm feedpoint impedance by using the cabling as shown above, but replace the quarter wave of 75 ohm coax from the coaxial "T" connectors to the dipoles with two eqaul convenient lengths of RG-62/U (93 ohm) or RG-133/U (95 ohm) coax. The half wave coaxial balun shown below will give you a 4:1 impedance step-up so you will have a good match to a 400 ohm folded dipole feedpoint. Although it is not necessary, purists can tweak the folded dipole's spacing until the SWR meter's needle does not move off the peg.

Whenever you make a coax balun always make it a bit longer than the calculated length. Do not forget to include the coax velocity factor in your calculations. Use a dip-meter to determine its resonant frequency, trimming it until it is tuned to the center of your band of operation, as shown below. I have made several coax baluns and the actual electrical length has never been exactly what the calculations said it should have been. My low SWRs always confirm the dip-meter length was right


SWR Measurements

The antenna should be as close as possible to where it will be permanently installed when you tune for the minimum SWR. A low SWR on a tall step ladder in your back yard (so you can tune it easily and have the SWR sensor attached to the antenna's coax feedpoint) may be fine for a rough cut tune after assembly. But it may need to be retuned again when in place on its mast or tower. It is usually not practical to get at your antenna's feed point once it is permanently raised and mounted. But how can you compare an SWR taken with the sensor on the antenna's feed point with an SWR when the sensor is connected to your antenna at the far end of a long run of coax? The chart below does this job nicely.


Coax Loss

How do you know for sure what your total line loss is for this chart? Use a coax attenuation chart? No way! You should test and log (in your station's log book) the loss of every coax section between your rig and antenna at the highest frequency it will be used. Test even those short 1 or 2 foot (30 to 60 cm) coax interconnection jumpers, and add them all together to get your actual total line loss.

Test each section with your SWR/power sensor first on the transmitter end, note your SWR (it should be 1:1) and your power in. Then put your sensor on the dummy load end. Note your power out and calculate your dB loss for each section. If you have never done this you may be in for some surprises. This is what convinced me to convert all of my 2 meters and higher coax lines to "N" connectors.

Don't forget to test accessories used in line with your coax. A local ham told me he found his brand new "N" connector coax switch had almost 6 dB of loss. I bought a new "PL-259-to-N" adaptor that I discovered had a similar loss.

Beware of cable marked RG-8/U TYPE (and other RG-* TYPE coax) as this means it does not comply to the specs for RG-8/U (or other RG-* specs) as far as loss and velocity factors. I bought some RG-8/U TYPE coax from a well known "cheap electronics" chain store that had unacceptable impedance bumps (detected as a high SWR) at splice points (those periodic bulges in the coax). Also the "good" sections had higher losses than shown in coax attenuation charts.

This same store sells cheap coax connectors that have higher impedance bumps (SWR) and losses than my Amphenol connectors. And when I tried to solder groundplane radials to this store's coax chassis connector, the center pin insulation melted and fell out of the metal case. Quality coax connectors now use teflon insulation which has low loss at high frequencies and has a high melting temperature. So beware of "cheap" coax and connectors, as you usually get what you pay for.

Some quality "RG-8/U TYPE" coax may be better than the specs, such as the coax Belden and other quality coax manufacturers produce. These companies publish their specs so you can compare them with the standard "mil-spec" coax. Take your handitalkie, SWR/wattmeter, dummy load and coax connector adapters with you when you go surplus shopping to see if that used coax or accessory is still good before you buy it.

The hassle of making special balanced dummy loads (to test baluns and matching sections) and taking the time to test all your coax sections and in-line accessories will pay for itself if you discover problems like those I discussed. In satellite work, every dB counts. Also, by adding up your total feed system loss and doing some simple calculations with your antenna gain figures you will be able to figure what your true EIRP is.

More practically, it will be a snap to trouble shoot any signal strength loss in the future. You will know what signal loss is normal. When you suspect your line loss has increased, measure the loss from your receiver to some convenient mid point, like where the coax leaves your room. If that loss is as expected, you know your trouble is between that point and the antenna. Repeat this "divide and conquer" search by testing the loss between the room entry and some mid point, like a preamp, and you will quickly locate the lossy component. Also you will know when it is time to change your coax by its increased loss, not its age.
9913 Coax

As the name of the game with satellite transmission lines is low loss, I have become fond of Belden's 9913 coax. Sure, hardline is better, but 9913 is easier. Once you pick up a few tricks and skills you will agree that installing "N" connectors on 9913 is much easier (and less lossy) than using the standard so-called "UHF" PL-259 connectors. To make a successful "N" coax connector fitting you must:

1. use the proper type connector with an oversized center pin (like Amphenol's 82-202-1006),
2. use vinyl plastic electrical tape (3 to 5 inches, 7.5 to 13 cm) wrapped around the coax end up against the "N"connector's shield clamp ring to provide a snug slip fit when assembled,
3. take your time and carefully make all cuts to a 1/64 inch (.4 mm) tolerance or better, then double check your dimensions when done,
4. use a small tube cutter so your cuts are all perfectly square and clean, leaving the shield unnicked, by ever so slowly tightening the roller blade as you cut (so you can stop just before you touch the shield), and
5. take your time fanning and trimming the shield so it lies evenly and smoothly over the entire clamp surface, but not beyond it to where it will interfere with assembly. No strands should cross.

Cut your coax a few inches longer than you need so you will feel free to cut off a fitting you are not happy with and try again until you get it right. Use what is referred to in ARRL publications as the "improved clamp" (like the Amphenol 82-202-1006) as it is easier to fabricate. Detailed fabrication illustrations with exact dimensions can be found in publications like The ARRL Handbook, The ARRL Antenna Book and The ARRL Electronics Data Book.

Stiff 9913 does not wear well where it must flex a lot, like where your coax leaves your boom up to your fixed attachment point on your mast or tower. Here a short run of RG-8/U will do better. If you already use 9913 for these flexing areas, you will eventually find kinks appearing at the points of most bending stress. This can be rectified by cutting 3 staggered lengths of RG-8/U that will go from the boom to beyond the kink. Secure them to the boom and the flexing 9913 with tape so they will take the bending stress and "round" the bend radius. Make these coax stiffeners long enough, with each piece at least an inch (2.5 cm) longer than the previous one so you are not soon faced with a new kink where the RG-8/U stiffener section ends.

My first circular polarized beam had the coax routed forward along the antenna boom to the elevation rotor boom up to the mast, where I had a small flex section. It is claimed that your circular polarization pattern is better if the coax is not attached along the boom but instead hangs from the boom's rear end and loops forward to the main mast. I did it this way on my next two beams. But I found no noticeable difference in performance on the air (where it counts) between these two coax routes. This is probably because we rarely get a perfectly circular polarized downlink signal. But I did notice more flexing problems with a long 9913 coax loop off the rear of the booms. A poorly made "N" connector may slip apart from the extra weight it must support on beams that have their coax connectors mounted 90 degrees to the beam's boom. Also I can no longer track an overhead pass horizon to horizon by tracking 180 with the elevation rotor. I am now limited to 90 degrees elevation and must change the azimuth heading 180 degrees at mid pass.

Although "N" connectors are said to be waterproof, I still feel better wrapping the connectors with sealing tape, like Coax-Seal (tm) which you then can mold after wrapping to exactly the way you want. This moldable tape is great for any coax weatherproofing, such as coax balun ends or feed points. Use several layers so the surface cracking that will occur with age will not go all the way through to the coax and connector. Linerless rubber splicing tape made for electricians by Scotch 3M (tm) is better for coax fittings, as it will not crack with age and is not so messy to remove. The overlapping rubber splicing tape flows together as it cures to become a solid rubber covering that needs to be slit lengthwise and peeled off to remove. Silicone outgases corrosive vapors that hasten shield corrosive damage. This will shorten the lifetime of your coax connectors.

Secure your coax, rotor lines and control cables with self locking plastic "zip" ties that are made for outdoor use, and are UV resistent. They are usually black. The white ties commonly used are for indoor use only. They will eventually break on their own if used outdoors. I like to use these ties at the end of my tape wraps to keep the end of the tape from lifting up with age.
Computer QRM

Computer birdies can ruin your best low loss run from your beam. The more sensitive your system, the louder these birdies get. Check to be sure all your computer and TNC cables are shielded with the shields attached to ground. I bought a "bargain" computer cable that did not connect the DB connector's mechanical ground shell to the cable's shield. Place wide copper or aluminum tape over all cracks, openings and poor fitting shielding inserts on your computer (like the metal strips for cable connectors on the rear of PC slot cards).

Most computers have a well vented and poorly grounded cabinet. Check out your cabinet and scrape the paint off all mating surfaces and under cabinet screw heads. Buy some copper screen and cut out pieces to go over all vent openings and the fan exhaust hole. Leave enough overlapping screen so you can easily mount the screen inside the cabinet. Run a solder bead along the screen's edges and reinforce ground attachment points where the screen can be screwed to existing cabinet screws. Add ground mount screws if you cannot secure the screen with existing cabinet screws.

After making a good ground system for your station, if you still have a problem with birdies, check everything connected to ground. Disconnect the ground straps one at a time to see if any ground connection will make your computer birdies decrease. I found one device that reduced my remaining birdies significantly when DISCONNECTED from my station's main ground strap bus. It was also connect to ground via coax connectors shields, so there must have been a ground loop radiating the birdies. These efforts have left me only two very faint computer birdies that are rarely encountered and easily covered by downlink signals when they are.

You should have EMI AC filters on your computer and rigs AC outlet or line. If you still have problems with birdies, disconnect each cable and line one at a time to determine what line is radiating your birdie. Wrap the offending cable several times through a toroid core on the end where the birdie is being generated to choke off the RFI flowing on this line's shielding.
Mode J Desense Filter

Desense problems awaits most mode JD and JA users. Although a quarter wave shorted coax stub will null out the offending 2 meters uplink signal, its loss on the downlink signal is unacceptable to me. The cavity desense filter does a better a job with no noticeable attenuation of the downlink signal. Have the plumbing store where you buy the copper pipes cut them for you. Be sure to make it clear that you need a precisely sized pipe that is cut without excessive blade pressure that might flare in the pipe ends.
Triac Antenna Control

Automatic antenna tracking is great, but the clacking of the relays inside your rotor control box every time the beams move is annoying. The circuit shown below does this switching silently. I sent this circuit to Brooks (of Kansas City Tracker) and he said this is how he does it at his station. He said he does not suggest this in his manual out of concern for liability in case people build it incorrectly and electrocute themselves or fry their computer. So be careful if you make this circuit and test it carefully when you are done. A fault can be lethal to you or your computer. Do not build it if you are not familiar with standard electrical safety construction practice. Consider yourself warned!

Coax Loss

How do you know for sure what your total line loss is for this chart? Use a coax attenuation chart? No way! You should test and log (in your station's log book) the loss of every coax section between your rig and antenna at the highest frequency it will be used. Test even those short 1 or 2 foot (30 to 60 cm) coax interconnection jumpers, and add them all together to get your actual total line loss.

Test each section with your SWR/power sensor first on the transmitter end, note your SWR (it should be 1:1) and your power in. Then put your sensor on the dummy load end. Note your power out and calculate your dB loss for each section. If you have never done this you may be in for some surprises. This is what convinced me to convert all of my 2 meters and higher coax lines to "N" connectors.

Don't forget to test accessories used in line with your coax. A local ham told me he found his brand new "N" connector coax switch had almost 6 dB of loss. I bought a new "PL-259-to-N" adaptor that I discovered had a similar loss.

Beware of cable marked RG-8/U TYPE (and other RG-* TYPE coax) as this means it does not comply to the specs for RG-8/U (or other RG-* specs) as far as loss and velocity factors. I bought some RG-8/U TYPE coax from a well known "cheap electronics" chain store that had unacceptable impedance bumps (detected as a high SWR) at splice points (those periodic bulges in the coax). Also the "good" sections had higher losses than shown in coax attenuation charts.

This same store sells cheap coax connectors that have higher impedance bumps (SWR) and losses than my Amphenol connectors. And when I tried to solder groundplane radials to this store's coax chassis connector, the center pin insulation melted and fell out of the metal case. Quality coax connectors now use teflon insulation which has low loss at high frequencies and has a high melting temperature. So beware of "cheap" coax and connectors, as you usually get what you pay for.

Some quality "RG-8/U TYPE" coax may be better than the specs, such as the coax Belden and other quality coax manufacturers produce. These companies publish their specs so you can compare them with the standard "mil-spec" coax. Take your handitalkie, SWR/wattmeter, dummy load and coax connector adapters with you when you go surplus shopping to see if that used coax or accessory is still good before you buy it.

The hassle of making special balanced dummy loads (to test baluns and matching sections) and taking the time to test all your coax sections and in-line accessories will pay for itself if you discover problems like those I discussed. In satellite work, every dB counts. Also, by adding up your total feed system loss and doing some simple calculations with your antenna gain figures you will be able to figure what your true EIRP is.

More practically, it will be a snap to trouble shoot any signal strength loss in the future. You will know what signal loss is normal. When you suspect your line loss has increased, measure the loss from your receiver to some convenient mid point, like where the coax leaves your room. If that loss is as expected, you know your trouble is between that point and the antenna. Repeat this "divide and conquer" search by testing the loss between the room entry and some mid point, like a preamp, and you will quickly locate the lossy component. Also you will know when it is time to change your coax by its increased loss, not its age.
9913 Coax

As the name of the game with satellite transmission lines is low loss, I have become fond of Belden's 9913 coax. Sure, hardline is better, but 9913 is easier. Once you pick up a few tricks and skills you will agree that installing "N" connectors on 9913 is much easier (and less lossy) than using the standard so-called "UHF" PL-259 connectors. To make a successful "N" coax connector fitting you must:

1. use the proper type connector with an oversized center pin (like Amphenol's 82-202-1006),
2. use vinyl plastic electrical tape (3 to 5 inches, 7.5 to 13 cm) wrapped around the coax end up against the "N"connector's shield clamp ring to provide a snug slip fit when assembled,
3. take your time and carefully make all cuts to a 1/64 inch (.4 mm) tolerance or better, then double check your dimensions when done,
4. use a small tube cutter so your cuts are all perfectly square and clean, leaving the shield unnicked, by ever so slowly tightening the roller blade as you cut (so you can stop just before you touch the shield), and
5. take your time fanning and trimming the shield so it lies evenly and smoothly over the entire clamp surface, but not beyond it to where it will interfere with assembly. No strands should cross.

Cut your coax a few inches longer than you need so you will feel free to cut off a fitting you are not happy with and try again until you get it right. Use what is referred to in ARRL publications as the "improved clamp" (like the Amphenol 82-202-1006) as it is easier to fabricate. Detailed fabrication illustrations with exact dimensions can be found in publications like The ARRL Handbook, The ARRL Antenna Book and The ARRL Electronics Data Book.

Stiff 9913 does not wear well where it must flex a lot, like where your coax leaves your boom up to your fixed attachment point on your mast or tower. Here a short run of RG-8/U will do better. If you already use 9913 for these flexing areas, you will eventually find kinks appearing at the points of most bending stress. This can be rectified by cutting 3 staggered lengths of RG-8/U that will go from the boom to beyond the kink. Secure them to the boom and the flexing 9913 with tape so they will take the bending stress and "round" the bend radius. Make these coax stiffeners long enough, with each piece at least an inch (2.5 cm) longer than the previous one so you are not soon faced with a new kink where the RG-8/U stiffener section ends.

My first circular polarized beam had the coax routed forward along the antenna boom to the elevation rotor boom up to the mast, where I had a small flex section. It is claimed that your circular polarization pattern is better if the coax is not attached along the boom but instead hangs from the boom's rear end and loops forward to the main mast. I did it this way on my next two beams. But I found no noticeable difference in performance on the air (where it counts) between these two coax routes. This is probably because we rarely get a perfectly circular polarized downlink signal. But I did notice more flexing problems with a long 9913 coax loop off the rear of the booms. A poorly made "N" connector may slip apart from the extra weight it must support on beams that have their coax connectors mounted 90 degrees to the beam's boom. Also I can no longer track an overhead pass horizon to horizon by tracking 180 with the elevation rotor. I am now limited to 90 degrees elevation and must change the azimuth heading 180 degrees at mid pass.

Although "N" connectors are said to be waterproof, I still feel better wrapping the connectors with sealing tape, like Coax-Seal (tm) which you then can mold after wrapping to exactly the way you want. This moldable tape is great for any coax weatherproofing, such as coax balun ends or feed points. Use several layers so the surface cracking that will occur with age will not go all the way through to the coax and connector. Linerless rubber splicing tape made for electricians by Scotch 3M (tm) is better for coax fittings, as it will not crack with age and is not so messy to remove. The overlapping rubber splicing tape flows together as it cures to become a solid rubber covering that needs to be slit lengthwise and peeled off to remove. Silicone outgases corrosive vapors that hasten shield corrosive damage. This will shorten the lifetime of your coax connectors.

Secure your coax, rotor lines and control cables with self locking plastic "zip" ties that are made for outdoor use, and are UV resistent. They are usually black. The white ties commonly used are for indoor use only. They will eventually break on their own if used outdoors. I like to use these ties at the end of my tape wraps to keep the end of the tape from lifting up with age.
Computer QRM

Computer birdies can ruin your best low loss run from your beam. The more sensitive your system, the louder these birdies get. Check to be sure all your computer and TNC cables are shielded with the shields attached to ground. I bought a "bargain" computer cable that did not connect the DB connector's mechanical ground shell to the cable's shield. Place wide copper or aluminum tape over all cracks, openings and poor fitting shielding inserts on your computer (like the metal strips for cable connectors on the rear of PC slot cards).

Most computers have a well vented and poorly grounded cabinet. Check out your cabinet and scrape the paint off all mating surfaces and under cabinet screw heads. Buy some copper screen and cut out pieces to go over all vent openings and the fan exhaust hole. Leave enough overlapping screen so you can easily mount the screen inside the cabinet. Run a solder bead along the screen's edges and reinforce ground attachment points where the screen can be screwed to existing cabinet screws. Add ground mount screws if you cannot secure the screen with existing cabinet screws.

After making a good ground system for your station, if you still have a problem with birdies, check everything connected to ground. Disconnect the ground straps one at a time to see if any ground connection will make your computer birdies decrease. I found one device that reduced my remaining birdies significantly when DISCONNECTED from my station's main ground strap bus. It was also connect to ground via coax connectors shields, so there must have been a ground loop radiating the birdies. These efforts have left me only two very faint computer birdies that are rarely encountered and easily covered by downlink signals when they are.

You should have EMI AC filters on your computer and rigs AC outlet or line. If you still have problems with birdies, disconnect each cable and line one at a time to determine what line is radiating your birdie. Wrap the offending cable several times through a toroid core on the end where the birdie is being generated to choke off the RFI flowing on this line's shielding.
Mode J Desense Filter

Desense problems awaits most mode JD and JA users. Although a quarter wave shorted coax stub will null out the offending 2 meters uplink signal, its loss on the downlink signal is unacceptable to me. The cavity desense filter does a better a job with no noticeable attenuation of the downlink signal. Have the plumbing store where you buy the copper pipes cut them for you. Be sure to make it clear that you need a precisely sized pipe that is cut without excessive blade pressure that might flare in the pipe ends.
Triac Antenna Control

Automatic antenna tracking is great, but the clacking of the relays inside your rotor control box every time the beams move is annoying. The circuit shown below does this switching silently. I sent this circuit to Brooks (of Kansas City Tracker) and he said this is how he does it at his station. He said he does not suggest this in his manual out of concern for liability in case people build it incorrectly and electrocute themselves or fry their computer. So be careful if you make this circuit and test it carefully when you are done. A fault can be lethal to you or your computer. Do not build it if you are not familiar with standard electrical safety construction practice. Consider yourself warned!

Antenna Masts

A low cost self supporting 40 foot (12 meter) mast can be made from a common 50 foot (15 meter) telescoping guyed TV mast. This is my double zepp antenna support mast, which I use for my 15 meters modes K and T uplink, a well as on all of the HF bands.

Extend each 10 foot (3 meter) section 5 feet (1.5 meters) and redrill the locking pin holes through both masts to secure them at half mast with a large stainless steel bolt, washer, lockwasher and nut. Mark a dark vertical line where the two masts telescope together so you can see how they should be positioned for the holes to line up. Then you will not have to hunt for the holes later when raising the masts. Use the circular clamp locking bolts that are at the top of each mast section to tighten out the slop between masts. You will end up with a self supporting 30 foot mast. I purchased two more 10 foot (3 meter) mast sections to similarly telescope into the top mast to extend my mast to 40 feet (12 meters).

For a base I dug a post hole and positioned a pipe vertically in the hole that just fit inside the bottom mast section. I filled the hole with concrete, leaving 4 inches (10 cm) of this pipe above the top. The bottom mast section was placed onto this pipe stub and secured with a bolt similar to the upper sections. A sturdy wooden frame was fabricated that was structurally attached to my house about 10 feet (3 meters) above the ground. The top of the first 10 foot (3 meter) mast section was securely clamped to this frame. This brace also provided a convenient point to tie my ladder while raising and lowering my antenna mast, giving me a safe and solid structure to work from.

This self supporting mast whipped (but did not break) more than I liked during a strong wind storm so I added a set of mylar guys near the top to keep it (and my SWR) rock steady. But as guys are not needed normally, I can raise and lower it by myself for antenna maintenance. Stainless steel hose clamps secured to the top of each section will keep each section from going too far inside the lower section when lowered. This is a convenient place to secure your open line stand-offs.

Guy wires are often a problem, as metal ones need ugly egg insulators, and even then you may end up with an unexpected resonant section. Common synthetic ropes have a stretch problem. Fortunately mylar rope has been designed specifically for antenna guying. When you use the proper size line, it is as strong as steel guy wire and its stretch, even on long runs, is negligible. The owners and staff of United States Rope (Note 4) will be happy to discuss the specs of their mylar guy rope with you. I used a set of mylar guys for 10 years before I decided it was time to replace them. The sun's UV light eventually weakens them, but in my experience, not any faster than my galvanized guys rusted. United States Rope tested my 10 year old line and found that although it was getting weaker, it still met the service specs I needed, so it was not about to fail.
Locating Materials

Getting supplies for antenna and other home brew projects can be a challenge. Check your telephone book's "Yellow Pages" for local electronics surplus stores. Sometimes "general" surplus and salvage stores will have an electronics section, or materials that you can use. Check local Universities and colleges as they often have public outlets where they dispose of their surplus electronic supplies and gear. Usually these sources are strictly "walk in" warehouses where sales staff will not know all that they have. Just wander around and look at all the goodies not normally available by mail or regular electronic suppliers. Cannibalizing cheap "junked" devices from these sources and from ham flea markets are good sources for "junk box" stock.

Additional sources for components for building projects can be found by going through the ads of ARRL and AMSAT publications. AMSAT and ARRL advertisers deserve your support as they help make these publications available at prices we can easily afford.

A Brief Introduction to Satellite Phone Networks

Over the last few years the use of satellite phones has been on the increase. They are now cheaper and more readily available than ever. However, this has not made it any easier for the consumer. With the choice of products on offer, how do you know which is the right one for you?
Popular Satellite Systems

Four satellite systems that have gained widespread popularity are Inmarsat, Iridium, Globalstar and Thuraya. Although they are all attempting to meet the same demand, they each go about it in different ways. Here's a basic overview of some of their strengths and weaknesses.
Inmarsat

The first mobile satellite system, Inmarsat is a great example of how the technology has emerged from a niche market and been made available to all. Originally designed for the maritime industry, they now have over 100,000 registered satellite terminals.
The Inmarsat Satellite Network

The Inmarsat network consists of four geo-stationary satellites 35,600km above the earth. The satellites are positioned at equatorial points over the Indian Ocean, the Pacific Ocean and the Eastern and Western sides of the Atlantic. The footprint created by this configuration is able to provide almost total global communication coverage with the exception of the North and South Poles. The first advantage that this gives Inmarsat is, once a signal is sent to a satellite, its individual footprint is often large enough to deliver that signal to its destination without having to transfer via another satellite first. This minimizes the risk of the signal being lost.

The main criticism that has been leveled against Inmarsat terminals is their size; they can be as big as laptop computers. Inmarsat rivals, Iridium, Globalstar and Thuraya, use handsets that are far more akin to cellular phones, which are handheld and do not need to be set up in a fixed location.
Inmarsat’s B–GAN Terminals

Inmarsat have now expanded their service with their next generation satellite system, B–GAN (Broadband Global Area Network). B–GAN delivers simultaneous voice and broadband through one single truly portable device.
Iridium

Iridium's mission was to create a satellite service that would provide truly global coverage, a service that no other satellite provider can currently provide. The Iridium system is the only provider of truly global voice and data solutions with complete coverage of the earth (except for Poland, Hungary, Sri Lanka and North Korea who have declined to support the service for political reasons). The Iridium satellite system provides global service across all ocean areas, air routes, and all landmasses, even the Poles
The Iridium Satellite Network

To achieve global coverage, the Iridium network uses 66 satellites, 450 miles high, orbiting the earth on 6 different planes. Traveling at 16,832 miles per hour, each satellite is able to circle the globe every 100 minutes. This configuration ensures that an Iridium handset will be able to send and receive calls from any location on the planet. As long as the handset has a clear line of sight to the sky, it will maintain communication with at least two satellites at any one time.

Iridium utilizes a portable handset with a large retractable antenna. Although still rather larger than a regular cell phone, the Iridium satellite unit is handheld and easy to carry. Whereas the Inmarsat satellite phone needs to be set up in a fixed location, the Iridium system even allows you to walk and talk.
Globalstar

Please note that Globalstar are currently experiencing problems with their satellites. This is resulting in some severe disruptions to service. As a result of this, Iridium is recommended as a handheld satellite phone solution.

The Globalstar network was developed with the business traveler in mind. Globalstar envisioned their customers as people who were working on the fringes of cellular networks, crossing in and out of coverage areas. Therefore, they designed their handset to work on the cellular CDMA networks as well as the Globalstar satellite network. There are 48 Low Earth Orbiting satellites which orbit the earth at an altitude of 875 miles.

The handheld phones are designed to switch seamlessly between the cellular networks and satellite network, even during a call. The phone will always use cellular networks if available. Only when there are not available will they link to the satellite network. By using this method the idea was to offer the best cost effective service, you would only use the more expensive satellite service when there was no alternative, (note though that roaming rates can be high with the cellular service).

Unfortunately, Globalstar has a limited coverage area. By operating on the CDMA standards, they have limited themselves to the localities where those standards are supported. At the moment, coverage includes the Americas, Russia and parts of Asia. Likewise their satellite network coverage area is limited compared to that of its rivals. Globalstar only offers service in around 100 countries, their territorial waters and some mid-ocean waters.
Thuraya

Thuraya offers dual band handheld phones operating on GSM cellular networks and Thuraya’s satellite services. Thuraya has roaming agreements with over 200 wireless cellular operators around the world, providing its customers the ability of using their Thuraya phones outside of satellite coverage.

Like Globalstar’s, Thuraya’s coverage is limited. There are 2 satellites in geo-synchronous orbit providing coverage in approximately 110 countries in Europe, parts of Africa, Asia, the Middle East and Australia.
In Summary

This information is not intended as a definitive guide to satellite phones. Rather, it is meant as a brief introduction to some of what is available. As you can see from the three examples highlighted, there is not one all encompassing system that can outperform its rivals in all areas. Each has certain strengths and certain weaknesses.

If you decide that you need to use a satellite phone, you need to decide which satellite network is best for you. You must assess which functions are most valuable to you. Do you need total global coverage? Do you need the ability to send and receive data? Do you want something that is easy to carry?

Once you are clear what you expect from satellite communication then you are able to make your decision from a more informed and confident position.

An Introduction to Mobile Phones for Travelers

“Hello? Is there anybody out there?” Years after Pink Floyd asked this famous question, chances are the answer is yes. Especially if you’re talking - pardon the pun - about mobile phones. Wherever they can be afforded, and even where they can’t, mobile phones are tremendously popular. The idea was developed in the late 1940s, although the product (and the technology) didn’t materialize for 30 years.

Mobile Phone Options:

On a very basic level, mobile phones use either digital or analog systems. Many digital phones have analog capabilities, however, analog systems do not have digital capabilities. A majority of mobile phones that are sold today use digital technology, with the exception of small, local carriers.

There are a number of different brands of mobile phones that use various systems to run their network. Without getting too technical, systems are the reason the phone you use in New York won’t get a signal in London and the reason the phone you bought in Paris works just as well in Cape Town.

What is it? What does it do?: Analog versus Digital

Analog: Analog cellular phones work like a FM radio, with a system of receivers, transmitters and frequencies. Like FM radio, there are a limited number of frequencies that can be used. This system works best for local coverage in rural areas, where there is less chance that a particular frequency would be in use. A few of the more popular analog systems are TACS, AMPS and NMT.

* TACS (Total Access Communications Service): European cellular monster Vodaphone started this system in 1985. Still used in a smattering of countries including Japan, Ireland, Tanzania and China.
* AMPS (Advanced Mobile Phone System): A United States brainchild in the 1980s - more or less obsolete now, but it’s available in every country in the western hemisphere, as well as American Samoa, Angola, China, South Korea, Lebanon, Nauru, Northern Mariana Islands, Solomon Islands, Turkmenistan, Uzbekistan, and Western Samoa.
* NMT (Nordic Mobile Telephone): Guess where this one started? NMT is a rival to TACS and AMPS. Its also found in many parts of Europe and a number of countries in Asia. With advancements in technology, NMT is slowly being phased out in a number of countries.

Digital: Modern phones are more likely to use this technology, which, if you actually care, uses a binary code of 0s and 1s (like the Matrix!). Unfortunately, there are a number of overlapping digital networks in place, and most phones are only compatible with one system. The four largest systems are listed below.

* GSM (Global System for Mobile Communications): While United States cell phone carriers were bickering among themselves and trying to one-up each other, European companies got together in 1982 and created the GSM system, which has since spread to Asia, Africa and the Pacific Rim. It is the only system that allows for calls in both Europe and North America, and one of three that provides for such advances as e-mail, fax, internet and wireless access. GSM was only introduced in the United States in 1995. The largest GSM carriers in America are T-mobile and Cingular. GSM comes in different bands depending on the country. Save money on GSM phone rental.
* TDMA IS-136 (Time Division Multiple Access): TDMA is also known as D-AMPS, if you actually care. The major US carrier is AT&T.
* PDC (Personal Digital Cellular): Although only found in Japan, it’s more widely used than anything besides GSM and TDMA IS-136 (D-AMPS).
* CDMA IS-95 (Code Division Multiple Access): CDMA technology has old roots - it’s a distant cousin of miliary communications from the second world war. The largest United States carrier on CDMA are Verizon and Sprint PCS.
* iDEN (Integrated Dispatch Enhanced Network): Motorola produces the phones for this system, which combines TDMA technology with that of hand-held radios. Nextel is the largest provider.

What is it? What does it do?: Phone Options

* Satellite: A satellite phone is the Grandfather of mobile phones. These large and clunky things (compared with today’s pocket-sized options) weigh about a pound and are capable of picking up a signal almost anywhere in the world, including the North and South Pole, the oceans and a number of remote areas. However, satellite phones are very expensive investments and mostly used by those on trekking or sailing expeditions.
* World: A world phone is a fancy description for a phone that is compatible with two or three bands of GSM. Make sure to buy an UNLOCKED world phone if you will be traveling through more than one country. An unlocked cell phone means you can change carriers and SIM cards, depending on the country you are in (more on SIM cards below). If you buy a locked phone, you will be unable to get a local number while you are traveling, and can be charged exorbitant roaming rates.
* Hybrid: A hybrid phone is just that - a phone that operates on two incompatible systems, such as iDEN and GSM.
* Country-specific/standard: If you are studying abroad for an extended period of time, or plan on sticking on one country for awhile, consider buying a standard mobile phone in that country. Watch out for contracts that extend pass your trip-time, however!

What is it? What does it do?: SIM cards and pre-pay options

GSM phones require the use of a SIM card - a small chip that is placed in the back of the phone that establishes your service provider and your cell phone number. Your phone will not work without it! You can buy SIM cards at any phone shop and if you have an unlocked phone, you can change your SIM card whenever you go to another country that offers the service (more than 170 around the world). This usually requires a minimum purchase of $20 or $30 worth of credit. A HopAbroad SIM card is available, and may be desirable for those traveling through a number of countries in a short period of time. Rates are higher for HopAbroad than country-specific SIM cards.

Many GSM phones are pre-paid. You can buy a specific dollar amount worth of credit, usually in increments of 5 or 10 dollars, at phone shops, convenience stores and tobacco shops. To top up your credit, dial the number given on the back of the card and enter in a credit number. Voilá, you have credit! Honest. It works. Unfortunately, pre-paid cards (and lack of GSM coverage) are not yet popular options in North America and can be a hassle.

Why You Should Bring a Mobile Phone

* Emergency use: Mobile phones are very common in the western world and one reason most parents justify buying their 13-year-old a phone is for safety. If you need to call a cab, or get lost, or simply need to dial an emergency number, a mobile phone can come in handy.
* Closer contact with family and friends: Lets face it. Sometimes, you just don’t want to track down a pay phone, let alone figure out how to work it. With a mobile phone, it is a lot easier to say in touch with your family and friends. This way, your friends can drunk-dial you in the middle of your day, and your mom can call whenever she wants (this can be good or bad). Plus, it’s a lot easier to arrange meeting up with people when you have a phone. An extra bonus? If you’re in a ‘home area’, incoming calls might be free.
* Organizational Tool: The cool thing about mobile phones is that they aren’t just phones any more. They’re alarms, schedulers and notebooks all in one. You can create short memos, calculate a tip and play simple computer games. Forget your phone? No problem, chances are, you’re camera is able to take a shot for you. Mobile phones can be a great resource for more than just calls.

Why You Should Not Bring a Mobile Phone

* Snooze, you lose: Phones disappear, like, all the freaking time. You leave them in the back of a taxi, you forget on top of the table at the restaurant, it falls out of your pocket when you’re being party hardy….you get the idea. Phones have legs. I’m convinced. Now, whether those ‘legs’ are the result of simply forgetting or losing your phone versus a wandering hand, I don’t know, but phones are small, and that’s not always a good thing.
* “Plugged In” feeling: If you have a cell phone, it’s a lot harder to get away. Sure, there isn’t service in the remote jungles of India, but there’s plenty of it in Europe or North America. Mobile phones are easy to get attached to and even easier to become dependent on.
* Fragile: The slippery little suckers always seem to be falling: off the bar, out of a purse, through someone’s hand, etc. Although some can take the beating, many can’t, especially when the fall is into water or an adult beverage.
* Price!: Boy, mobile phones are expensive, and we’re not even talking about the phone itself! Roaming rates, new batteries, SIM cards, top-up points - they’ll all get you right in your pocketbook. Text messages, incoming calls and outgoing calls add up, especially if you’re not careful or you get confused on the price schedule.
* Hassle: Charging batteries, figuring out roaming rates, dealing with converters, worrying about it getting lost…are you sure a mobile phone is worth the effort?

Satellite Phone

A satellite phone or satphone is a mobile phone that sends and receives calls using satellites rather than landlines or cellular broadcasting towers. A satellite phone only requires a clear line of sight to the sky. The advantage of a satellite phone is that it can complete calls from anywhere. A satellite phone can operate in the middle of the Sahara desert, at the top of Mount Everest, or from a clearing deep within a South African jungle. It is an indispensable tool for remote excursions of all kinds, and provides solid communication on the seas and in the air.

A disadvantage of a satellite phone is a noticeable delay in conversations. The signal must first travel to the satellite, then to an earthbound gateway before being routed to the receiver. The receiver's response will follow the same path in reverse, taking equally long to reach the caller. Satellite minutes are also more expensive than cellular minutes.

However, these drawbacks are irrelevant when considering the function that a satellite phone serves. It can create a link to civilization from places where no other link is available. It also allows loved ones to stay in touch, as in the case of researchers, adventurers and those in the military, and it can provide backup communication in disasters when cellular towers or landlines might not be functional.

The three main satellite networks at present are Iridium, Globalstar and Thuraya. Iridium uses low orbiting satellites that minimize conversational delays, but more importantly, it is the only current satellite network that provides coverage over the entire earth, including the oceans. Competitor Globalstar covers about 80% of the earth's landmasses, excluding northern and southern polar regions, while Thuraya covers parts of India, Asia, Africa, the entire Middle East and Europe.

For those who only wish to use a satellite phone on rare occasions, one can rent rather than buy. Rental fees start at about US$40 per week, but this does not include talk time, which can run as high as $1.75 per minute. If buying a satellite phone outright, a contract is necessary with a satellite network, or prepaid cards may be purchased. Minutes are less expensive with a contract than when renting or buying prepaid, but are still more expensive than cellular minutes.

Satellite phones range in price according to network coverage areas. Iridium phones are more expensive because they can make calls from anywhere in the world. One current entry-level Iridium satellite phone sells for US$1,275, while other network phones start out at about half that price, and can be found for less. Because satphones are so expensive, they are often purchased used.

Some satellite networks have partnered with cellular GSM networks to provide Internet service and email through satellite phones in addition to offering GSM roaming. This allows a satellite phone customer that lives or works at the fringes of a GSM zone to utilize GSM networks when possible, and satellite calls when necessary. Such built-in flexibility is ideal for military, disaster or relief contractors, rural ranchers, local boaters, or anyone who requires or desires guaranteed regional or global coverage.