Soyuz Radio Systems

Sven Grahn

Short-wave radio systems

All the early versions of Soyuz had an extensive short-wave communications system for both AM voice and for CW-PDM telemetry. 15.008 MHz and 20.008 MHz were used almost exclusively for telemetry, while the frequencies around 18 MHz were used for AM voice. 18.035 MHz was used on Soyuz-1.

18.060 MHz AM voice has also been reported from Soyuz-9 and Soyuz-18 (when docked to Salyut 4). The onboard transmitter power on short waves was 3 Watts. Simplex voice was probably the most common but as we know from the observations of Chris van den Berg duplex was also possible with reception of AM voice from the ground on 22.205 MHz.

HF is still used on late model Soyuz spacecraft during the recovery phase, when Morse code (the Morse-code characters AN) and AM voice can be transmitted on 18.060 MHz. Morse code beacon (AN) only is transmitted on 8.364 MHz during recovery operations. The antenna is a whip antenna that is stored as a rolled-up steel band under a little door in the upper part of the re-entry vehicle (See picture).

VHF voice system

The Soyuz VHF communications system probably has used the same set of frequencies since the programme's  inception (with two exceptions noted below). The 121.75 MHz FM voice link is well known and radiates about 4 Watts with a deviation of D = 10-30 kHz. With an audio bandwidth of b = 3.5 kHz the resulting bandwidth is (according to "Carson's rule"): 2 * D + 2 * b = 27-67 kHz.

The VHF voice communications system probably operated both in simplex and duplex mode. In the duplex mode 130.167 MHz is the uplink and 121.75 MHz is the downlink. In the simplex mode 121.75 MHz is used in both directions. However, in Mir flights 130.167 MHz has been used for downlink and it is feasible that even early Soyuz craft could use this as an alternate downlink in the duplex mode (with 121.75 MHz as uplink). It is difficult to locate the antennas for the VHF voice on early models of Soyuz. The devices marked Antenna? in the figure above could possibly be such antennas.

For ASTP and Soyuz 22 the frequency 142.417 MHz was used for downlink FM voice so that 121.75 MHz could be used for inter-ship communications with Apollo-18.

VHF Telemetry system

VHF telemetry has always been transmitted from Soyuz vehicles in the 160-200 MHz band. The most commonly observed frequency is 166.0 MHz. Before Soyuz-T the modulation type used was PPM-AM.

This system has been replaced by the PCM-FM system called BR-9TsU-3 also operating on 166.0 MHz. The transmitter power is about 7 Watts. Soyuz 16, 19, and 22, the ASTP models of Soyuz also transmitted PCM-FM telemetry but, on 192.0 MHz. The data rate in the PCM version is 256 kbps.

Early Soyuz version had U-shaped antennas at the tip of the solar panels. The eariest model, 7K-OK, had the U-shaped antennas at the "rear" tip of the solar panels. The ASTP vehicles (Soyuz 16, 19 and 22), 7K-TM, had these antennas at the midpoint of the outer edge of the solar panels. In (1) the omnidirectional charcteristics of such an antenna is described. A simple sketch of the principle of the antenna is hown on the right.

UHF Television system

The Soyuz television system operates on 463 MHz. Nowadays it is called the "Klest" system. The TV standard on Soyuz is SECAM (625 lines transmitted at 25 frames per second). A black-and-white video signal with 6 MHz bandwidth is transmitted by frequency modulating the carrier creating an RF bandwidth of 20 MHz. using Carson's rule we can the deduce that the deviation is 4 MHz. The transmitter power is 10 Watts.

The antenna is a "crossed slot" design shown on the right. This sketch was made by myself after examining the Soyuz-4/5 full scale mock-ups displayed at the Soviet Space Exhibition in Stockholm in 1978.

Command-radio link

This system operates on 768.96 MHz on the uplink where 64 bps data rate is used. The command reception antenna is the band of dipoles seen around thge waits of the spacecraft.

Commands are downlinked to provide a verification of receipt. The frequency of this downlink is922.75 MHz. The antenna system for this frequency consists of two half-wave loops (See picture) mounted 180 degrees apart on a band that circles the orbital module. Just behind the dipoles there is a disk, which is believed to contain the 2.7-2.9 GHz radar transponder antenna.

The details of this antenna "ensemble" is shown in the figure on the right (see also picture), which is based on a sketch that I made after examining the Soyuz-4/5 full scale mock-ups displayed at the Soviet Space Exhibition in Stockholm in 1978.

Both low rate command-copy signals  and wide band telemetry signals have been observed on the downlink. It is also probable that Klest TV signals can be routed through this transmitter. The transmitter power is probably about 10 Watts.

Radar transponder system

For radar measurements of the orbit a radar transponder is installed that picks up the pulses from a ground radar station at typically 2725 MHz and re-transmits the signal at typically about 2860 MHz. Radar pulses are about 1 microsecond long. The RF bandwidth of the radar signals, which is mainly determined by the rise and fall time of the radar pulses, is about 12 MHz. The transmitter peak pulse power is probably around 100 Watts. There may be an acquisition-aid beacon on 2900 MHz.


  1. Schultz, John (W2EEY/1), CQ, Jan 1967, p.64

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