
    Amateur Satellite Communications 


    On the Wings of a DOVE 

         DOVE is one of several Microsats presently in orbit. They're 
    called Microsats because of their tiny size (9 inches on each 
    side). Its primary mission is education. DOVE transmits streams of 
    packet telemetry and occasional bulletins on 145.825 MHz FM. By 
    studying the telemetry, you can learn all sorts of fascinating 
    things about conditions in space. Since DOVE is a LEO (Low Earth 
    Orbiting) satellite, its signal is very easy to hear. 
         If you only want to listen, you'll get an earful of raucous 
    packet bursts as it streaks overhead. DOVE also has digital voice 
    capability and may be transmitting in that mode from time to time. 
         If you have packet equipment, you're in for an extra treat. 
    Set up your TNC as you would for normal operation and switch your 
    FM transceiver to 145.825 MHz. As DOVE rises above the horizon 
    you'll begin to see streams of data flowing across your monitor. 
    You may also see brief text bulletins. 
         After you get tired of watching raw data, you'll want to find 
    out what it means. There are several programs available to decode 
    DOVE telemetry. For more information, send a self-addressed, 
    stamped envelope to: AMSAT, 850 Silgo Ave, Silver Spring, MD 
    20910. Ask for their software catalog. 



    The Mir Space Station 

         Mir has been occupied by Russian cosmonauts for several years 
    as a laboratory for testing human responses to long-duration space 
    flights. To combat boredom, an Amateur Radio station was 
    installed. The cosmonauts pass amateur license tests and are 
    assigned special Mir call signs (such as U5MIR) prior to launch. 
    When they reach the station, they operate 2-meter FM voice or 
    packet. 
         Like the DOVE satellite, Mir's signal is powerful. You'll 
    usually find it on 145.55 MHz, and you won't need sophisticated 
    equipment to hear it--or to be heard. Once again, an outside 
    antenna--such as a ground plane--works fine. Its orbit provides a 
    couple of very good "passes" each day for most areas. 


    Mir on Packet 

         The Mir Amateur Radio station uses standard 1200-baud AFSK 
    packet--the same packet format you use for QSOs here on earth. The 
    Mir packet station includes a mailbox where you can leave messages 
    for the cosmonauts (or anyone else) and pick up their replies. 

    
    Voice Contacts with Mir 

         The Mir cosmonauts obviously enjoy packet, but sometimes they 
    crave the sounds of other human voices. You may be waiting for a 
    chance to connect on packet, only to hear them calling CQ instead! 
         Working Mir on voice is very similar to working a DX pile up. 
    You sit with microphone in hand and wait until you hear the 
    cosmonaut complete an exchange. At that moment you key the mike 
    and say your call sign. Now listen. No response? Call again 
    quickly! Keep trying until you hear him calling you or someone 
    else. 
         The major problem with working Mir--on voice or packet--is 
    its erratic schedule. The cosmonauts have many daily assignments 
    and are not always able to find the time to operate their amateur 
    station. They are sometimes forced to turn off their equipment 
    altogether to avoid interference to other systems during critical 
    tests. 
         Another problem concerns Mir's orbit. The space station 
    travels at a relatively low altitude, so it's always subject to a 
    significant amount of atmospheric drag. If it didn't occasionally 
    "boost" to a higher orbit, the station would reenter the 
    atmosphere and be destroyed. Every time Mir fires its rocket 
    engines to adjust its orbit, a revised set of orbital elements 
    must be distributed. If you want to try your luck with Mir, plan 
    to update your elements for the space station as often as 
    possible. 


    The RS (Radio Sputnik) Satellites 

         Have your ever heard of RS-10/11 or RS-12/13? They are 
    unmanned Amateur Radio satellites placed in orbit by the former 
    Soviet Union. Without a doubt they are among the easiest 
    satellites to work. 
         The RS satellites are completely different from DOVE, Mir or 
    the space shuttle. They are basically orbiting repeaters riding 
    piggyback on larger satellite platforms. RS-10 and 11 are carried 
    by COSMOS 1861, and RS-12 and -13 are part of COSMOS 2123. There 
    are two RS satellites per platform (which is the reason for the 
    dual designation), but only one satellite is active at a time. All 
    RS satellites are equipped with unique devices called linear 
    transponders. 


    Linear Transponders 

         Earthbound repeaters listen on one frequency and repeat what 
    they hear on another. Imagine what would happen if your local 
    repeater could retransmit everything it heard on an entire group 
    of frequencies? This is exactly the function of a linear 
    transponder. 
         In mode A, the RS satellite transponder listens to a portion 
    of the 2-meter band and retransmits everything it hears on the 10-
    meter band. When mode K is active, the transponder listens to a 
    section of the 15-meter band and simultaneously retransmits on 10 
    meters. In mode T, the satellite listens on 15 meters and 
    retransmits on 2 meters! The range between the highest and lowest 
    uplink (or downlink) frequencies is known as the transponder's 
    passband.
         Not only do linear transponders repeat everything they hear 
    on their uplink passbands, they do so very faithfully. CW is 
    retransmitted as CW; SSB as SSB. FM voice transmissions are 
    strongly discouraged since their broad signals occupy an enormous 
    chunk of the downlink passband. Not only would this limit the 
    number of stations that could use the satellite, it would place a 
    severe drain on transponder power.


    NOTE: As this was written, RS-10 had been locked into Mode A and 
    RS-12 in Mode K


         Elaborate antennas are definitely not required to work the RS 
    satellites. A wire dipole is fine for receiving the 10-meter 
    downlink signal. By the same token, a basic ground plane is 
    adequate for your 2-meter uplink. In terms of power, 20 to 30 
    watts seems to work well.


    
    The PACSATs 

         If you enjoy packet operating, you'll love the PACSATs! 
    Several satellites comprise the PACSATs: AMSAT-OSCAR 16, Webersat-
    OSCAR 18, Lusat-OSCAR 19, Fuji-OSCAR 20, UoSat-OSCAR 22 and 
    KITSAT-OSCAR 23. 
         OSCAR 20 (also known as FO-20) is essentially an orbiting 
    packet bulletin board. It even uses commands similar to 
    terrestrial bulletin boards. You can pick up and deliver packet 
    mail on OSCAR 20 as well as read the latest general-interest 
    bulletins. 
         OSCARs 16, 19, 22 and 23 are known as "file servers." (OSCARs 
    16 and 19 are Microsats.) You can access these satellites only by 
    using specialized PACSAT software available from AMSAT.
     The AMSAT software permits highly efficient uploading and 
    downloading of files as the satellites pass overhead. 
         OSCAR 18--known as WO-18, or Webersat--is especially 
    fascinating. Another member of the Microsat family, OSCAR 18 
    carries an on-board camera and transmits digitized images of the 
    earth, sun and other objects in space. Once again, special 
    software--available from AMSAT--is required to view Webersat 
    images. OSCARs 22 and 23 also carry on-board cameras.


    PACSAT Equipment 

         Like the other satellites we've discussed so far, the PACSATs 
    do not require large antennas and hefty amounts of RF power. (A 
    few watts to an omnidirectional antenna is perfectly adequate.) 
    However, the PACSATs operate in mode J: a 2-meter uplink with a 
    70-cm (437 MHz) downlink. You may already own a 2-meter FM 
    transmitter suitable for the uplink, but you'll need a 70-cm SSB 
    receiver for the downlink. Most hams use 70-cm all-mode 
    transceivers for downlink reception. An alternative is to use 
    receive converters to shift a 70-cm signal down to 10 meters for 
    reception on standard HF rigs. 
         The PACSATs use a variety of data rates and signal formats. 
    Special PSK modems must be used with your TNC to communicate with 
    the satellites.

    

    OSCAR 13 

         There is one satellite that travels in a high, elliptical 
    orbit and it's a DX powerhouse: AMSAT-OSCAR 13! OSCAR 13 (or AO-
    13) is a sophisticated Phase 3 satellite that incorporates several 
    frequency modes and highly sensitive receivers. It supersedes 
    AMSAT-OSCAR 10 which was still "alive" as of this writing, but 
    damaged and difficult to control. 
          OSCAR 13 has an orbit that acts like a slingshot, shooting 
    it out to an altitude of 30,000 km at its apogee. During the high 
    point of its orbit, OSCAR 13 seems to be nearly motionless from 
    our perspective here on earth. While a certain amount of antenna 
    aiming is required, very little additional movement is necessary 
    once the antennas are in their proper positions. From its high 
    vantage point, OSCAR 13 "sees" a great deal of the earth. This 
    opens a window to DX contacts on a regular basis! 
         The downside to having such a high-altitude orbit is that 
    more transmitted power is needed to access the satellite and a 
    weaker signal is received here on earth. You'll need high-gain, 
    directional antennas to operate OSCAR 13. The more gain you have 
    at the antenna, the less power will be required at the 
    transmitter. You'll need to be able to rotate the 2-meter and 70-
    cm antennas vertically and horizontally (elevation and azimuth). 
         Mode B (70-cm uplink/2-meter downlink) is the most popular 
    mode on OSCAR 13 and it's the easiest mode for the beginner. A 2-
    meter SSB/CW receiver is required for the downlink and a similar 
    70-cm transmitter is necessary for the uplink. Considering the 
    weak signals, a 2-meter mast-mounted preamplifier is also a worthy 
    addition to your OSCAR 13 station. 
         Like the RS satellites, OSCAR 13 employs a linear 
    transponder. SSB and CW are the modes of choice, although QSOs 
    tend to be longer and more relaxed. With OSCAR 13 you don't have 
    to worry too much about losing the satellite in the middle of your 
    conversation! For more information on operating OSCAR 13, see the 
    ARRL Operating Manual or the Satellite Experimenter's Handbook. 



    Finding the Satellites 

         How can you know when a satellite is about to make an 
    appearance in your neighborhood? To answer that question you need 
    to know the satellite's orbital elements.

         As incomprehensible as it may seem, an orbital element set is 
    merely a collection of numbers that describes the movement of an 
    object in space. By feeding the numbers to a computer program, you 
    can determine exactly where a satellite is (or will be) at any 
    time. Don't worry about the definitions of Mean anomaly, Argument 
    of perigee and so on. If you're curious, get a copy of the 
    Satellite Experimenter's Handbook (available from your favorite 
    dealer or the ARRL) and you'll learn all about those definitions--
    and more. For the moment, consider the words as labels for the 
    numbers that appear beside them. 

    Finding the Elements 

         There are several sources for orbital elements: 

    o Satellite newsletters 
    o W1AW RTTY and AMTOR bulletins 
    o Packet bulletin boards 
    o Telephone bulletin boards 
    o AMSAT nets 

         If you have an HF radio, RTTY capability, a packet TNC, a 
    telephone modem or the necessary cash for a subscription, you'll 
    always be able to get the latest orbital elements for the 
    satellites you want to track. If all else fails, there is probably 
    someone in your area who has access to the elements. Ask around at 
    your next club meeting.  


    Using the Elements 

         Computers are common in most Amateur Radio stations today. If 
    you have a computer in your shack, you're in luck! There are many 
    programs on the market that will take your orbital elements and 
    magically produce satellite schedules. 
          Among other things, the programs tell you when satellites 
    will appear above your local horizon and how high they will rise 
    in the sky (their elevation). When working satellites, the higher 
    the elevation the better. Higher elevation means less distance 
    between you and the satellite with less signal loss from 
    atmospheric absorption. 
          Some programs also display detailed maps showing the ground 
    track (the satellite's path over the ground). AMSAT (the Radio 
    Amateur Satellite Corporation) offers satellite tracking software 
    for a variety of computers. For more information contact: AMSAT, 
    850 Silgo Ave, Silver Spring, MD 20910, tel 301-589-6062. 

    
