Soyuz telemetry bursts

Sven Grahn

Kosmos-140 was launched into a 165-218 km, 51.6 deg orbit at 0322 UT on 7 February, 1967 and gave the Kettering Group its first sample of Soyuz-type telemetry on shortwaves. Actually, neither myself nor Geoff Perry had the opportunity to pick it up, but Ken Edwards, the Senior Technician at the Physics Department at the University College of Wales, Aberystwyth, chart-recorded signals on 20.008 MHz which Geoff identified as originating from Kosmos-140. He did this during automatic monitoring the nearby frequency of 20.005 MHz for signals from Explorer 22. These were later found to be the typical PDM telemetry of a Soyuz. (It was subsequently learned that TASS had given the frequency 20.008 MHz in its launch announcement).

Aberystwyth picked up the signals on revolutions 5, 21, 22, and 23. (On rev 5 the spacecraft passed right over Aberystwyth and the signals on the chart below were recorded). On all occasions the signals were transmitted in bursts: 30 seconds on and 90 seconds off. This behaviour enabled Geoff to identify Kosmos-186 as a Soyuz-type spacecraft during the automatic docking mission Kosmos-186/188. Similar behaviour was observed with the Kosmos 212/213 mission and, with this, it was discovered that the telemetry was actually transmitted on 15.008 MHz during part of the off period on 20.008 MHz.

In connection with ASTP, detailed information about the command-signalling device in the Soyuz cockpit showed that the Soyuz short-wave transmitter could be cycled through four different frequencies, presumably to cover all possible HF bands so that at least one 30 second burst would get through - independent of spacecraft location - a very clever emergency signalling system.

What frequencies were used? Well, I think they were 20.008 MHz, 15.008 MHz as observed and also 18.060 MHz (originally 18.035 MHz) and one more frequency which is not known..! Or perhaps the fourth slot was to be used for voice?  20.008 MHz, 15.008 MHz and 18.060 MHz (originally 18.035 MHz) were the only Soyuz frequencies ever given in official TASS announcements!

Signals on shortwaves from Soyuz also were often observed all along the orbit which explains the interest in the frequency hopping exercise to try to find the frequency that best propagated around the world. The simple keyed beacon signal propagated all around the earth in what is called "ionospheric wave ducts" giving an effect often called "the whispering gallery effect". A peculiarity observed during "whispering gallery propagation" was that the signal from the Soyuz increased abruptly as the spacecraft reached the antipode. At that point all HF signal energy radiated horizontally reached the antipode! We used to call this the "antipode effect".

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