Microwaves And The Amateur Satellite Program

The OSCAR satellite program utilizes several amateur microwave bands, and future projections call for yet more use of these bands . OSCAR8, for example, produced a mode-] output on 70 em that could easily be received by basic amateur setups. The OSCAR 9 satellite includes beacon transmitters operating in the 13-cm and 3-cm bands, which again reflects the wave of future events. OSCAR Phase III satellites are projected to afford communication capabilities in the 23-cm, 13-cm, and 3-cm bands, thus our amateur microwave spectrum may become quite popular and commonplace during the mid 1980s. See Fig. 1-7.





















Fig. 1-7. OSCAR 8, a Phase-II Amateur Radio satellite, orbits approximately 800 miles above the Earth, where it relays 7D-cm,2-meter, and to-meter signals. Future (Phase-III) spacecraft will use 432, 1260, and 10,000 MHz to provide hemisphere-wide communications capability.

The microwave spectrum, with its reliable line-of-sight propagation, is particularly appealing for future geostationary (Phase III) OSCAR satellites. Relatively large dish antennas can be directed at these satellites, resulting in very dependable communications. Through the use of earth-based microwave OSCAR links, one or two spacecraft may be interlinked for near global communications. Future OSCAR satellites are destined to be recognized as prime users of amateur microwave frequency allocations.

The microwave spectrum in its entirety promises to be a major factor in future amateur-radio pioneering. The vast bandwidth allocations, combined with computer communications and other advanced technology forms, will permit this range to be used in a heretofore unrealized manner. Dependable and reliable amateur communications with distant lands will be provided by long range OSCAR satellites, while cross-country microwave networks will provide nationwide signal linking.

Hand-help FM transceivers will also gain "seven-league boots" through microwave links and FM-to-SSB converters situated at OSCARsatellite uplink points. Also, EME systems may use moonbased microwave repeaters. Amateur pioneering efforts, however, will not cease ; a creditable rise of interest in radio astronomy will serve as proof of that situation.

The following chapters of this book describe, in easy-tounderstand form, the exciting world of amateur microwave operations. Separate discussions of the history of microwaves, getting started in microwaves, and detailed information on equipment and operations on various bands is included. This works is thus a guide for microwave newcomers. Here's your invitation and join the excitement of this challenging amateur frontier. Come on along and get in on the action! See Fig. 1-8.




















Fig. 1-8. A view of the future of Amateur Radio communications? A 10-GHz Gunnplexer and 2-meter hand-held transceivers combine to expand the horizons.

Microwave and EME

The microwave range has, for many years , been synonymously related to amateur moonbounce activities . Centering on the 70-cm, 23-cm and 13-cm bands, amateurs have often successfully communicated over this Earth-Moon-Earth path. The parameters associated with moonbounce are many: they include considerations of atmospheric losses, faraday rotation, moon-encountered losses, galactic noise interference, etc. A general outline of these parameters is illustrated in Fig. 1-6.

The Earth-Moon-Earth distance varies between 225,000 miles (perigee) and 250,000 miles (apogee), producing fluctuations of up to 2 dB of reflected signals-a difference between communicating and not communicating via this difficult path. The EME signal is also masked by a variety of noises and requires top-notch earthstation setups plus high-gain antennas and high transmitted power levels for ensured success. The minimal acceptable rf-output power is 400 watts, and the minimal antenna-gain figure is 20 dB. These parameters do not allow any leeway for additional signal fades or noise, thus one can logically surmise that EME communications reflect extreme challenges for only the stout hearted!





















Fig. 1-6. Some of the many parameters affecting uhf and microwave EME signals.

The full aspects of EME communications are beyond the scope of this book, thus the reader is referred to more specialized works in this particular area. Rest assured that additional information and equipment for EME operations will be a natural part of tomorrow 's innovations.

Higher Bands

The 15-mm and higher amateur microwave bands represent truly challenging and unpioneered frontiers in communications. Until recent times, the prime drawback to amateur operations in this range has been a lack of available gear, parts, and technical information.

Again, Microwave Associates of Burlington, Massachusetts, has recognized this situation and provided a means of ' operation. Special Gunnplexers for 24 GHz and (upon special order) 48 GHz are available for less than the cost of many 2-meter transceivers. This inspiring challenge can open new doors for amateurs, and firmly establish those involved as pioneers ini microwave history. What else could one ask? Yes, today 's Golden Age of Radio is alive and well-particularly in the unpioneered regions of microwave communications! See Fig. 1-5.

















Fig. 1-5. Author Dave Ingram, K4TWJ, makes preliminary focal-point adjustments in a 10-GHz Gunnplexer and 3.5-foot dish antenna to be used in a microwave link . The system is capable of relaying amateur high-frequency band signals or amateur television (ATV) signals.

3 cm

The 3-cm (10-GHz) amateur band is gaining popularity at a very creditable rate. The primary equipment used for these 10-GHz activities is the Gunnplexer. The Gunnplexer has a Gunn diode located in its 10-GHz cavity , which is directly mated with its waveguide and horn-antenna system. The complete 10-GHz unit functions as a "front end" for a lower frequency unit that acts as an i-f stage. A small portion of the transmitted signal from each Gunnplexer is used as the receiver's local oscillator .

A further clarification of this technique is shown in Fig. 1-4. The two communicating Gunnplexers are frequency separated by the amount of the desired i-f, which is 146 MHz in this example. Both Gunnplexer transmitters remain on continuously, thus providing a local oscillator for mixing with the 10-GHz signal from the other unit. The ultimate result is a 146-MHz signal appearing at the i-f port of each Gunnplexer.

These 3-cm communications systems have proven their abilities over paths of 100 miles (160 km), and several European amateurs have communicated over 500 km (310 miles) on 10 GHz. An attractive plaque , sponsored by Microwave Associates of Massachusetts, awaits the first 3-cm pioneers to break the 1000-km (621 mile) range on this unique band. Gunnplexer communication networks are ideally suited for data communication links and multichannel TV relays, and as such could truly mark the direction for future .developments in amateur communications.










Fig. 1-4. A basic Gunnplexer communications system for 10 GHz. Each Gunnplexer oscillator provides energy for transmitted signal and couples a small amount of that energy into a mixer for heterody ning the received signa l down to an i·f range. The two transmitter signals are separated by the frequency of the chosen i-f.

5 and 10 em

The 10 cm and 5 cm amateur bands have received miniscule interest during the past, primarily due to the lack of effective gear capable of operation in this range. The recent escalation of interest in satellite-TV terminals capable of operating in the 3.7- to 4.2-GHz range, however, shows great promise in ratifying that situation. Since many telephone companies utilize frequencies between 5 and 10 em for broadband relays of multiple voice links, evolutions may also provide a surplus of modifiable gear for radio amateurs.

13 cm

The 13-cm amateur band holds particular appeal for future amateur activities. Its proximity to the MDS band permits use of inexpensive 2-GHz downconverter receiving systems and 2.3 GHz transmitting gear in a very cost-effective manner.

A group of amateurs in a given area can actually become operational on 2.3-GHz for a lower expenditure than on almost any other amateur band. Direct communications on 2.3 GHz typically range from 20 to 60 miles, depending on terrain and the antenna systems employed. This spectrum is especially attractive for such wideband signals as multichannel fast-scan TV, multiplexed data links, computer interlinks, etc.

A number of 2-meter repeaters could also be linked via 2.3 GHz, and the line-of-sight propagation would permit ' peaceful coexistence of several of these services in any particular metropolitan area.

MDS and Satellites

Situated between the amateur 23 cm and 13 cm bands are two particularly interesting commercial services. The weather satellite band used for studying cloud formations from approximately 20,000 miles above earth employs 1691 MHz while the public carrier service of MDS (acronym for Multipoint Distribution System) employs the range of 2100 to 2150 MHz.

Although reception of weather satellites has previously appealed primarily to commercial services, numerous amateurs are realizing the advantages of this capability,and are constructing their own receiving systems. Several inexpensive receiving kits have been recently introduced for satellite reception.

The MDS band may best be recognized by its recently dubbed nickname of "microwave TV braodcasting." Carrying restricted- type viewing similar to cable-TV programming, microwave-TV systems operating in the 2.1 GHz range are springing up across the nation. Reception of these pay-TV signals may be accomplished through the use of relatively inexpensive 2.1 GHz downconverters.

Additional information concerning this commercial activity is presented later in this book. The United States space shuttles also use the 2.2-to 2.4-GHzrange during flights. Numerous educationaltelevision services also frequent this spectrum for point-to-point relays .

23 cm

The next amateur band is 23 cm, or 1240 to 1300 MHz. It should also be mentioned at this point that 1,000 MHz is equal to 1 gigahertz, or GHz. The 23-cm band may thus be referred to as 1.24 to 1.3 GHz, if desired. The 23-cm band is becoming quite popular in many areas of the United States and Japan. Numerous amateur fast-scan-TV repeaters operate near the 1265 MHz range, and Phase-IV OSCAR satellites are slated to use the lower portion of this band for uplink signals. Equipment for 23-cm operation can be relatively inexpensive if the amateur shops carefully and plans his moves. Inexpensive varactor-tripler circuits for translating a 432-MHz signal to 1296 MHz may be constructed with minimum effort, and the results are quite gratifying. Receiving downconverter "front ends" for 23 em are available in kit form, or preassembled from several sources listed in monthly amateur magazines. Such converters usually feature high-gain, low-noise, rf sections, and relatively low purchase costs. A substantial'amount of 23-cm equipment is slated to become available for amateur use in the near future, thus activity on this band is destined to significantly increase. The long-distance communication record on 23 em stands at 1,000 miles-a feat accomplished by using emperature-inversion and signal ducting propagation.

860 MHz

Slightly higher in frequency, the next amateur band is 860 to 890 MHz. This allocation was acquired as this book was being written, thus its applications and future in amateur radio are unknown at the present time. This band is expected to become an amateur fast-scan-TV/OSCAR-satellite range. Its proximity to the upper end of uhf television channels is particularly appealing for public-service applications during emergencies, or for public-relations use .

The Low End

Almost every amateur is familiar with the 144-MHz (2-meter) amateur band. FM, SSB, and amateur-satellite communications are used rather extensively in this range throughout the United States and most of the world. As the 2-meter band filled with amateur activity, operations expanded to 220 MHz. As a number of FM repeaters became operational in this spectrum, activity once again expanded to include the 440-MHz(70-cm) amateur band. The 70-cm band is primarily used for FM, amateur fast-scan television, and OSCAR (Orbital Satellite Carrying Amateur Radio) amateur communications.

THE MICROWAVE SPECTRUM

The frequencies comprising the microwave spectrum extend from approximately 1,000 megahertz, or 1 gigahertz, to approximately 50,000 megahertz, or 50 gigahertz. The upper end of this range is somewhat undefined, and indeed unpioneered, when visualized in respect to general amateur applications . A list of amateur frequencies available is shown in Fig. 1-3.While the 144, 220, and 432 MHz allocations are not microwave frequencies, they are included here as a reference to known and established amateur areas. Likewise, the MDS and satellite TV bands (2.1 and 4 GHz) , are shown as a means of familiarizing the amateur with the microwave spectrum.





















Fig. 1-3. Frequency allocations in the microwave spectrum.

THE EARLY DAYS AND GEAR FOR MICROWAVES

Although a little known fact, experiments in the microwave spectrum date to the very early days of radio pioneering. A number of Heinrich Hertz's early experiments with "Hertzian waves" during the late 1800s were at wavelengths which translate to frequencies of between 400 and 800 MHz. Guglielmo Marconi's early European experiments in radio utilized simple spark-gap equipment with small coils; the accompanying receiver also used basic "hooks" of wire. Translating the physical dimensions of this primitive gear to its corresponding wavelength and frequency yields an rf spectrum of approximately 1.5 to 3.0 GHz. Microwave communications have, indeed, been with us since the early days of radio activity.

Continuing toward our present period of time, we find a somewhat crude version of the magnetron tube developed during the mid-1920s. This unique tube used a strong magnetic field, created by large magnets surrounding the device, to deflect electrons from their natural path and thus establish oscillation in the microwave range. Because specific technology wasn't yet available for putting the device to use, however, the magnetron laid (basically) dormant for several additional years.

The European continent was also reflecting significant pioneering efforts in the microwave spectrum. A 2-GHzlink was operated across the English Channel during the mid 1930s. During the 1940s, the cavity magnetron was devised and placed into use with the first RADAR (RAdio Detecting And Ranging) systems.

Ensuing evolutions during subsequent decades produced the klystron, reflex klystron, the traveling-wave tube, the Gunn diode, and the recent GaAsFET transistors. The difficulties in developing these microwave devices revolve primarily around electron transit time for each cycle of wave propagation. Stated in the simplest of terms, electrons leaving the cathode of a tube (and traveling toward that tube's plate), must transit a path shorter than one-half wavelength. This situation is not of consequence in low-frequency devices; however, an alteration of design is required for microwave operations. The lighthouse tube (by General Electric) , and acorn tubes were introduced to fulfillthis need. By directing electron flow in more direct patterns while reducing stray and interelectrode capacitance, these devices allowedmicrowave operations at frequency ranges that were previously not feasible. As knowledge expanded , higher and higher frequencies became practical. The restrictions of stray capacitances and transit times were overcome, and "tuned circuits, " such as they are for these extremely-high frequencies, were incorporated directly into the new devices.

The Amateur's Microwave Spectrum

The electromagnetic spectrum of microwave allocations is one of the hottest and fastest-rising frontiers in amateur communications technology. This unique frontier offers a true kaleidoscope of unlimited challenges and opportunities for today's innovative amateurs. Although a relatively uncharted area until recent times , today's microwave spectrum is gaining a widespread popularity and rapidly increasing acceptance. This trend shows no signs of waning; indeed, microwave communications are destined to mark the path of future developments in amateur communications. These communications will include all modes, from data packeting and multichannel television relays to multichannel voice links of FM, SSB, and computer interlinks. While the line-of-sight propagation associated with microwave communications would seem to restrict its capabilities , such is not necessarily the case. This situation has been commercially exemplified in such arrangements as longdistance telephone microwave links, television microwave networks , etc. These systems provide broadband cross-country and intercontinental linking. Transcontinental linking has been accomplished by geostationary communications satellites. Amateur radio is destined to progress in a similar manner; furthermore, amateur satellites capable of providing these interconnect functions are being developed at this time. The future of amateur radio looks quite promising and very exciting , and microwave communications will playa major role in its developments.

The h-f band operator of today might ponder the logic of using microwave communications. Why switch from the populated rf areas to a seemingly vast, empty, range of extremely-high-frequency spectrum, when few amateurs operate that range? One reason is that the line-of-sight propagation of microwaves affords reliable and predictable communications , independent of solar or weather conditions. Extended communication ranges are possible using one, two or more microwave repeaters. Additionally, the wide bandwidth associated with such repeaters allows multiple communications to be simultaneously conducted .

The following example may further clarify this situation: Assume two amateurs living in metropolitan areas separated by one (or two) mountains. They desire to set up a fast-sean-television repeater station. Although an in band 70-cm (420 MHz) system could be used, it would require expensive filters and duplexers for effective operation, and that operation would carry only one transmitting ' signal at a time. A crossband fast-scan repeater operating with an input on 70 cm and an output on 23 cm (1240 MHz) or 13 cm (2300MHz) would alleviate the problems and costs of special filters and duplexers. However, its operation would still be confined to only one transmitting signal at a time. Thinking ahead, the two amateurs would set up a relatively inexpensive 10 cm (2300 MHz) or 3 cm (10,000 MHz, or 10 GHz) "bare bones" repeater station for relaying their signals across the mountainous area. At any later time, other amateurs c04.1d join the activity simply by adding the appropriate microwave " front ends " to their setup . An additional microwave link could then be added at one, operator's location for further feeding the signals to other interested amateurs. Each new addition to the network would carry its own weight in equipment support/finance, causing the system to grow and expand precisely in the direction ofmost interest. The original two network-instigating amateurs are now part of a multioperator system.

Further, let's assume several amateur-radio computer enthusiasts, plus some amateur RTTY (radio teletype) operators , and a number of voice-only operators desire to join the network. The vast bandwidth capability of this system stands ready to accommodate the new group of amateur operators: only minor alterations in power levels and antenna configurations are necessary.

The network continues to grow until several communities and cities are linked in a totally reliable and predictable manner. An amateur satellite uplink/downlink is added to the network, along with electronic-mailbox and intelligent-voting systems, .plus emergency/priority interrupts for special requirements. The network ultimately spans coast to coast and continent to continent, conveying many forms of amateur-radio activity. Each new area would be responsible for its own expenditures, and thus the system carries its own weight. The original instigators, plus many fellow operators, now enjoy multimode communication from small, personal, transceivers that access the network via simple 2-meter, 70-cm, or newly introduced 13-cm units.

Science fiction? Hardly. A vision into the near future? Surely. Realizing the many beneficial aspects of microwaves, only one of which has been exemplified here, we can truly calculate that amateur operations during this and subsequent decades will flourish through utilization of all available assets-and the microwave spectrum is one of these prime assets. A simplified example of the previous discussion is shown in Fig. 1-1.





















Fig. 1-1. Simplified overview of a basic microwave network that can be expanded to cover many areas and modes.

Moving in a slightly different direction, let's now consider a more personal application for which microwaves could again prove useful. An individual microwave link can be used for remote highfrequency receiving setups. Several wideband converters, for example, can be connected to respective antennas and used for reception of all hf bands. The resultant wideband spectrum may then be microwave relayed to an amateur's home location or transmitter site. Following retrieval of the h-f spectrum from the microwave receiver's output, conventional signal processing can be utilized for producing a truly optimum DXing setup, The signal diversity creates unique capabilities which thus allow a station to perform in a definite "top-gun" manner. See Fig. 1-2.





















Fig. 1-2. Basic arrangement for a remote receiving site linked by 10-GHz microwave equipment.