By: John A. Magliacane, KD2BD
[This article originally appeared in The AMSAT Journal, Volume 15 No. 4, July/August 1992]
Radio Sputnik (RS) satellites are favorite starting points on the road to Amateur satellite communications. These satellites provide consistent service, strong downlink signals, and have very sensitive transponders, making them easily accessible to even the most modest Amateur satellite ground stations.
On December 17, 1981, six new RS satellites were launched together on a common launch vehicle. RS-3 and RS-4 were experimental satellites and did not contain transponders for general use. The remaining satellites contained 40 kHz wide Mode A linear transponders. In addition, RS-5 and RS-7 both contained "autotransponders" called ROBOTS. Autotransponders made it possible to carry on a CW telegraphy contact with the ROBOT computer carried on the satellite. Upon calling the satellite on a ROBOT uplink frequency, the spacecraft would respond with short message and issue a QSO number.
The autotransponders made it possible to carry out a CW contact on the satellite even if there were no ground stations available on the transponder at the time.
After RS-5 and RS-7 had ceased operating, RS-10 and RS-11 were launched into a safer 1000 km altitude circular low-Earth orbit. Both RS-10 and RS-11 share a common power bus and space platform with COSMOS 1861, a Russian navigation satellite. Like their predecessors, RS-10 and RS-11 both contain 40 kHz wide Mode A linear communication transponders and ROBOTS, but they also contain new "Mode K" and "Mode T" transponders which have uplink passbands in the 15-Meter Amateur band. No other Amateur communications satellite had used 15-Meters for an uplink before.
On February 5, 1991 the latest group of RS satellites, RS-12 and RS-13, were launched along with COSMOS 2123, another Russian navigation satellite. These RS satellites are virtually identical in capability to RS-10 and RS-11. All four Radio Sputniks are alive and well and in operation at the present time.
For Modes K and T, usually less than 100-watts of transmitter power and a dipole antenna are needed for the uplink. Regardless of the transponder mode, most of the emphasis should be placed on the sensitivity of the downlink receiver, because "if you can't hear 'em, you can't work 'em"!
Proper operating practice dictates that the transmitter or receiver operating on the highest frequency band be tuned in compensation for Doppler shift during a QSO. This means on Mode A, the transmitter VFO should be adjusted while the downlink receiver remains fixed. 0n Modes K and T, the transmitter VFO should remained fixed while the downlink receiver is adjusted for proper performance.
This practice not only applies to RS satellites, but remains valid for ALL Amateur transponder operations, and helps to avoid collisions between ground stations at geographically diverse locations as they experience varying magnitudes of Doppler shift.
Almost everyone who gives RS satellite operation a try is hooked after their first contact. After the pass is complete and the log book has been updated, you'll find them plotting out their strategy for the next pass. Since the RS series of satellites are in a circular orbit, orbital predictions are easy using OSCARLOCATORS or simple orbital prediction software.
The beacons transmit CW telegraph and provide spacecraft telemetry, ROBOT downlinks, and "Codestore" messages carrying news bulletins from the spacecraft command station RS3A.
At the present time, RS-10 is active on Mode A, while RS-12 is operating on Mode K. During periods of high solar flux, many satellite enthusiasts worked other stations a half a world away through RS-12 Mode K while the spacecraft was well below the horizon of each station. These sub-horizon contacts were made possible through F-layer propagation.
"CQ CQ DE RS10 QSU 145820 KHZ AR"after which the ROBOT will listen for call on 145.820 MHz. Calling the ROBOT is easy. Simply call the satellite, give your callsign, and end with AR. For example:
"RS10 DE KD2BD AR"The ROBOT uplink passband is several kilohertz wide, so extreme uplink frequency accuracy is unnecessary. Even chirpy CW signals have been found to work well. If the ROBOT does not copy your callsign correctly, it may ask for a repeat and respond with "QRM", "QRZ", or "RPT". Successful contacts are rewarded with ROBOT response complete with a QSO number such as:
"KD2BD DE RS10 QSO NR 386 0P ROBOT TU USW QSO NR 386 73 SK"High-speed CW works best for calling the ROBOT. The ROBOT will respond at the speed it is called.
QSL cards are available through the Radio Sputnik coordinating group:
Radio Sport Federation
Fig. 1 - Satellite: RS-10 NASA Catalog Number: 18129 Analog Transponders: Uplink Downlink Mode K: 21.160 - 21.200 Mhz 29.360 MHz - 29.400 MHz Mode T: 21.160 - 21.20O MHz 145.860 MHz - 145.900 MHz Mode A: 145.860 - 145.900 Mhz 29.360 Mhz - 29.400 MHz Mode KT: 21 MHz uplink into 29 and 145 MHz downlinks Mode KA: 21 MHz and 145 MHz uplinks into a common 29 MHz downlink Beacons: 29.357 MHz, 29.403 MHz, 145.857 MHz, 145.903 MHz Robot Uplinks: 21.120 MHz, 145.820 MHz
Fig. 2 - Satellite: RS-11 NASA Catalog Number: 18129 Analog Transponders: Uplink Downlink Mode K: 21.210 - 21.250 Mhz 29.410 MHz - 29.450 MHz Mode T: 21.210 - 21.250 Mhz 145.910 MHz - 145.950 MHz Mode A: 145.910 - 145.950 Mhz 29.410 MHz - 29.450 MHz Mode KT: 21 MHz uplink into 29 and 145 MHz downlinks Mode KA: 21 MHz and 145 MHz uplinks into a common 29 MHz downlink Beacons: 29.407 MHz, 29.453 MHz, 145.907 MHz, 145.830 MHz Robot Uplinks: 21.130 MHz, 145.830 MHz
Fig. 3 - Satellite: RS-12 NASA Catalog Number: 21089 Analog Transponders: Uplink Downlink Mode K: 21.210 - 21.250 Mhz 29.410 MHz - 29.450 MHz Mode T: 21.210 - 21.250 MHz 145.910 MHz - 145.950 MHz Mode A: 145.910 - 145.950 Mhz 29.410 MHz - 29.450 MHz Mode KT: 21 MHz uplink into 29 and 145 MHz downlinks Mode KA: 21 MHz and 145 MHz uplinks into a common 29 MHz downlink Beacons: 29.408 MHz, 29.454 MHz, 145.912 MHz, 145.958 MHz Robot Upinks: 21.130 MHz, 145.830 MHz
Fig. 4 - Satellite: RS-13 NASA Catalog Number: 21089 Analog Transponders: Uplink Downlink Mode K: 21.260 - 21.300 Mhz 29.460 MHz - 29.500 MHz Mode T: 21.260 - 21.300 Mhz 145.960 MHz - 145.000 MHz Mode A: 145.960 - 146.000 Mhz 29.460 MHz - 29.500 MHz Mode KT: 21 MHz uplink into 29 and 145 MHz downlinks Mode KA: 21 MHz and 145 MHz uplinks into a common 29 MHz downlink Beacons: 29.458 MHz, 29.504 MHz, 145.862 MHz, 145.908 MHz Robot Uplinks: 21.138 MHz, 145.843 MHz