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.