Some satellites transmitted only while above the horizon in the USSR, although others transmitted continuously. In the latter case, they could be heard over any point on the globe and, from a given location, it was possible to hear a transmission from thousands of miles away. There were occasions when signals would arrive simultaneously by two different routes through the ionosphere. They would have different values of Doppler Shift and gave the impression that there were two separate signals. Only by analysing the signal content was it possible to determine that the source of both transmissions was the same.

From the UK, tracking of Cosmos satellite recoveries and the associated beacons at 19.995 and 20.005 MHz was limited to the period April-October due the seasonal variation of the state of the ionosphere. In winter months, the signal just did not come through.

The beacon transmissions usually lasted for about six minutes as the recoverable cabin descended under the parachute. Occasionally, under very favourable ionospheric conditions (usually late spring-summer, weak transmissions would continue for longer periods providing that the aerial had not earthed itself electrically by contact with the ground. There is a description of the Cosmos recovery beacons elsewhere on the Zarya web site.

NOTE - for afficionados of the Kettering Satellite Tracking Group, these photographs of Derek Slater and Bob Christy are separated by 31 years in time.

This list is not an exhaustive one - it contains frequencies that the author was active in tracking and announced frequencies from the launching agency. Some Cosmos/Soyuz entries are by way of example in that they are typical of a particular satellite or spacecraft type - there were many more similar transmissions.

By definition, HF is a frequency of 30 MHz or less. Some of the earlier HF-transmitting flights used coherent frequencies in the low part of the VHF band - up to 90 MHz, they are included in this list for reference and because they do not fit comfortably elsewhere.