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Satellite Radio Frequencies


Tyneside, UK
2020 Aug 7
Friday, Day 220

Maintained by:




















Transmissions from HEO on the AFSATCOM Channels

Satellites in highly eccentric 'Molniya' type orbit were used by the US for slow speed radio teletype (RTTY) communications using FSK (Frequency Shift Keying). The downlink signals were strong and easily detectable with simple equipment such as a hand held receiver with its factory-supplied whip aerial.

Transmissions were reported also from satellites in geosynchronous orbit but they were not detectable in the UK because the satellites in question are below the local horizon. There are unsubstantiated reports that the uplinks could be intercepted in some parts of the continental United States. AFSATCOM transmissions (from HEO at least) ceased in 2008.

AFSATCOM Frequency Plan D

The AFSATCOM bandplan consists of rwelve channels, each with specified frequencies for the uplink and downlink. When it a signal is received on the uplink, it is shifted down by a set amount (72.900 MHz) and retransmitted.

The bandplan is formed symmetrically. The first two and last two channels (numbers 1/2 and 11/12) have a spacing of 10 kHz between them. The remaining channels are each 5 kHz from their neighbours.

The frequency pairings are:

Channel Uplink (MHz) Downlink (MHz)
 1316.595243.695
 2316.605243.705
 3316.610243.710
 4316.615243.715
 5316.620243.720
 6316.625243.725
 7316.630243.730
 8316.635243.735
 9316.640243.740
10316.645243.745
11316.650243.750
12316.660243.760


Signals Received

The content of the signal signal transmitted from the satellite is reversed compared with the signal that was received. A channel with nothing on its uplink is transmitted as a CW tone so it is possible to distinguish between an empty channel and a non-transmitting one. As of 2006 June, downlink channels 1-8 and 10-12 were carrying RTTY links, some with frequency shift of approximately 2.7 kHz and some with approximately 2.1 kHz. Channel 9 had a single carrier, making it very useful for measuring the Doppler shift.

From time to time, the transmit frequency is shifted downwards (approx 168 second intervals) by about 20 Hz in order to counteract the changing Doppler shift experienced by ground stations.

There is a detailed description of how AFSATCOM was working in the Satellite Tracking area of the Zarya web site and it can be found by following the link in the right hand menu.

Freq (MHz) Satellite Transmission Notes
243.695
USA 125
1996-038A
23945
CW - RTTY-style data US comms and intelligence gathering: AFSATCOM Channel 1, no longer transmitting.
243.695
USA 137
1998-005A
25148
CW - RTTY-style data US comms and intelligence gathering: AFSATCOM Channel 1, no longer transmitting.
243.705
USA 125
1996-038A
23945
CW - RTTY-style data US comms and intelligence gathering: AFSATCOM Channel 2, no longer transmitting.
243.705
USA 137
1998-005A
25148
CW - RTTY-style data US comms and intelligence gathering: AFSATCOM Channel 2, no longer transmitting.
243.710
USA 125
1996-038A
23945
CW - RTTY-style data US comms and intelligence gathering: AFSATCOM Channel 3, no longer transmitting.
243.710
USA 137
1998-005A
25148
CW - RTTY-style data US comms and intelligence gathering: AFSATCOM Channel 3, no longer transmitting.
243.715
USA 125
1996-038A
23945
CW - RTTY-style data US comms and intelligence gathering: AFSATCOM Channel 4, no longer transmitting.
243.715
USA 137
1998-005A
25148
CW - RTTY-style data US comms and intelligence gathering: AFSATCOM Channel 4, no longer transmitting.
243.720
USA 125
1996-038A
23945
CW - RTTY-style data US comms and intelligence gathering: AFSATCOM Channel 5, no longer transmitting.
243.720
USA 137
1998-005A
25148
CW - RTTY-style data US comms and intelligence gathering: AFSATCOM Channel 5, no longer transmitting.
243.725
USA 125
1996-038A
23945
CW - RTTY-style data US comms and intelligence gathering: AFSATCOM Channel 6, no longer transmitting.
243.725
USA 137
1998-005A
25148
CW - RTTY-style data US comms and intelligence gathering: AFSATCOM Channel 6, no longer transmitting.
243.730
USA 125
1996-038A
23945
CW - RTTY-style data US comms and intelligence gathering: AFSATCOM Channel 7, no longer transmitting.
243.730
USA 137
1998-005A
25148
CW - RTTY-style data US comms and intelligence gathering: AFSATCOM Channel 7, no longer transmitting.
243.735
USA 125
1996-038A
23945
CW - RTTY-style data US comms and intelligence gathering: AFSATCOM Channel 8, no longer transmitting.
243.735
USA 137
1998-005A
25148
CW - RTTY-style data US comms and intelligence gathering: AFSATCOM Channel 8, no longer transmitting.
243.740
USA 125
1996-038A
23945
Channel usually occupied by an unmodulated carrier US comms and intelligence gathering: AFSATCOM Channel 9, no longer transmitting.
243.740
USA 137
1998-005A
25148
Channel usually occupied by an unmodulated carrier US comms and intelligence gathering: AFSATCOM Channel 9, no longer transmitting.
243.745
USA 125
1996-038A
23945
CW - RTTY-style data US comms and intelligence gathering: AFSATCOM Channel 10, no longer transmitting.
243.745
USA 137
1998-005A
25148
CW - RTTY-style data US comms and intelligence gathering: AFSATCOM Channel 10, no longer transmitting.
243.750
USA 125
1996-038A
23945
CW - RTTY-style data US comms and intelligence gathering: AFSATCOM Channel 11, no longer transmitting.
243.750
USA 137
1998-005A
25148
CW - RTTY-style data US comms and intelligence gathering: AFSATCOM Channel 11, no longer transmitting.
243.760
USA 125
1996-038A
23945
CW - RTTY-style data US comms and intelligence gathering: AFSATCOM Channel 12, no longer transmitting.
243.760
USA 137
1998-005A
25148
CW - RTTY-style data US comms and intelligence gathering: AFSATCOM Channel 12, no longer transmitting.
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