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Sidebar to DXCC on RS-12
By Don Daso, WZ3Q
QST August 1995
RS-12 was launched from Plesetsk, Russia, on February 5, 1991, attached to the COSMOS 2123 navigation satellite. Its orbit is 620 miles above Earth, and it circles the globe every 105 minutes in a polar orbit 83° above the equator. Moving from pole to pole, with the Earth turning under it, means the satellite will pass you between 4 and 11 times each day. The number of passes is 4 near the equator, while N4ZC gets 6 passes daily from his location at 35° N latitude.
You can think of the satellite as a repeater with an input frequency on 21 MHz and an output on 29 MHz. You can transmit on any frequency permitted by your license within the 40 kHz uplink window (21.210-21.250 MHz) and listen within the 40 kHz downlink window (29.410-29.450 MHz). A CW beacon on 29.408 MHz may be heard when the satellite is within range. You'll hear a string of letters and numbers at 25 wpm. The RS-12 transponder operates in a proportionally linear fashion; if you transmit on 21.210, your output will be on 29.410. The output frequency varies slightly--what's known as "Doppler shift"--because of the speed of the moving satellite. As RS-12 moves towards you, downlink signals move down in frequency. Generally, all signals drift in frequency as you listen to the downlink, but this isn't a problem once you become accustomed to it. Don't move your transmit frequency; simply shift your receiver to keep stations tuned in during the QSO. This is different from other satellite operation, like OSCAR, where you do move your transmit frequency, but the chances of interfering with someone are greater on 21 MHz than on 70 cm, especially considering propagation, so shift your receive frequency only.
There's no mode limitation on RS-12, but it's accepted practice to use CW on the lower part of the 40 kHz window and USB in the upper portion. Other standard practices include learning the offset. An easy way to remember where to set your transmit frequency is to use the last two numbers. For example, if you hear a station you want to call on 29.431, remember 31, and set your transmitter on 21.231. As long as both VFOs are in the correct uplink/downlink window, you'll be close to the right numbers.
Having two VFOs is the only hard requirement, and that's easily met. Two rigs with two antennas or a separate receiver are ideal, but one rig with antennas for both bands will work. Just about any antenna system will work; big beams aren't needed for RS-12.
Hearing yourself helps because if you can hear yourself, you can work anyone within the footprint of the satellite. And if you can hear yourself, you'll work people outside the footprint of your tracking program--people below the horizon. Having a second receiver helps because, as Roger says, "People will answer you, but they'll be on 15 meters. They won't know what 'CO satellite' means. I've heard QSOs where people thought they were making a satellite contact, but it was really just a terrestrial 15-meter exchange. You need to ask, 'Are you listening to me on 10 meters?' Be specific because they won't know what you mean otherwise. A clue is the signal report they give you. If it's a 59 or 599, they're probably hearing your terrestrial 15-meter signal. I've rarely heard RS-12 at S7. It's usually between SO, right in the noise floor, and S5. Another indication is that if they're exactly zero beat with you on 15 meters, chances are good they're responding to your uplink signal, not your 10-meter signal."
A beam, although not necessary, can increase your chance of success when working at or even below your horizon. Working RS-12 3° below your horizon can provide you an extra minute of time at each end of your workable window. This time can be critical to DX success on the satellite.
"The tracking program sometimes won't indicate a usable pass. When the satellite is 1° below the horizon, for instance, it won't show up on my program, but you can maximize your DXCC exposure by using passes just below the horizon. You have to watch for them, though, because they happen every third day. RS-12 is ever so slowly drifting eastward. These below-the-horizon passes, when they occur, extend your country possibilities."
Propagation plays an important role with RS-12. You sometimes hear stations within the uplink window who are working for normal terrestrial QSOs. You sometimes hear stations skipping into the satellite on 21 MHz. Even if they're knowledgeable about RS-12, they might not hear the downlink on 29 MHz--the maximum usable frequency (MUF) simply isn't high enough. Knowledge of propagation can enable you to make contacts on over-the-horizon paths. Over-the-horizon paths, or those near the horizon, sometimes sound odd, like a signal passing over the pole in the auroral zone. At times, conditions require you to switch to CW to complete your QSO. Another problem is caused by this satellite being above the F layer. At times of high MUF, the 29 MHz signal may make it through, but the 21 MHz signal can't make the path, especially when the satellite is low on the horizon.
