Radio systems of L1 and LOK series of spacecraft

Sven Grahn


Deductions from external features of L1 Zond spacecraft

Zond and Soyuz share the same basic design, but there are differences between the craft. The differences in outward appearance between Soyuz and Zond that relate to radio systems can be summarized as follows:

Information from other sources

Very little information used to be available in the public domain about frequencies used by the Zond system. In the past only informal information was available to support the assumption that a 922.76 MHz downlink was used. However, a recent Russian publication (1) provides plenty of detail of the radio system. This source indicates that the basic Saturn-MS ground stations were also used for early Soyuz and Salyut missions and gives the uplink as "770 MHz" and the downlink as "920 MHz", which confirms the early guesses as to frequency. The sketch below from (1) (my translations of the captions) shows the various signalling modes on this basic link. Interestingly, the command-verication signals have been heard from early Soyuz, Progress and Salyut craft around 925.24-925.25 MHz, which is indeed 2.5 MHz from the center frequency, just as indicated below. Listen to the command-verification signal from Soyuz-34 in June 1979 here .

Informal hints from personal acquaintancies mention 183 MHz as a downlink. The analysis of the pictures of Zond seem to support the use of the old 183/102 MHz TT&C systems as a back-up.

However, the whip antennas on the solar panel tips are difficult to tie to a specific downlink frequency. It is difficult to envisage that 76-80 MHz was used in deep space, since the "Tral" telemetry system that used this frequency range was a wideband system operating in low earth orbit. It seems more reasonable to assume that the whips were used for a frequency near 40 MHz, perhaps the same type of simple telemetry that was transmitted by the early Luna probes on 39.986 MHz. 

Summary

It seems reasonable to conclude that the main telemetry, command and tracking link used by Zond 4-8 was the 922.76 MHz downlink with the uplink at 768 MHz. In addition a back-up system using omni antennas seems to have operated on the old Soviet deep space TT&C system that used 183.6 MHz as a downlink and 102 MHz as an uplink. Perhaps 40 MHz was used for very low rate housekeeping telemetry. 

L3 radio systems

According to (1) the LOK vehicle used the same frequencies as L1, i.e. 922/768 MHz and also a VHF uplink. Here is a translation of a sentence from Molotov's book:

"... The meter-band (106 MHz) was used for a "request signal" in a noncoherent channel, while the working frequency of the reply channel was shifted by 6.5 MHz with respect to the frequency of the coherent channel ..."

By "the coherent channel" Molotov probably means 922 MHz. In all probability this non-coherent uplink on 106 MHz was a back-up command link. It is not easy to find an antenna for this frequency on sketches of LOK. Perhaps the little rod in the picture below is this antenna. In other sketches there appears to be at least two such antennas.


Sources

  1. E.P. Molotov, Terrestrial radio systems of space vehicles (2004), p. 75
     

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