UHF-Satcom.com - Meridian / Molniya HEO monitoring Updated: (01/01/2011 15:08:12 -0000)
On the 2nd of December 2010, 'skyking' reported to the Hearsat-L mailing list that around 278MHz, US air traffic control was being heard whilst beaming North from the UK. After some coordinated monitoring of the downlinks, members of the #Hearsat IRC channel determined that the most likely source of the signal was the Meridian-2 Russian military communications satellite that was built as a replacement series for the Molniya satellites. If you are also interested in monitoring the Meridian satellites, PLEASE come to the #hearsat IRC channel to coordinate your experiments with other enthusiasts!! A suitable antenna for 278MHz reception is described below, it is a scaled version of the WA5VJB 'cheap' Yagi originally designed for 222MHz ham radio operation.
|6 Element WA5VJB Yagi design centred on 278MHz.
Note: Spacing starts at the Reflector, and is total spacing between reflector and the relevant element. All dimensions are in centimetres. Note, this is designed for a non conductive boom, and elements of 2 or 3mm diameter. More info at http://www.wa5vjb.com/yagi-pdf/cheapyagi.pdf
The Meridian-2 transponder might look like that shown in the following FFT screenshots;
Canadian Apogee showing 277.8MHz signal, and several air traffic control relays around 278.4MHz
Russian Apogee showing the transponder noise floor and several air traffic control relays around 278.4MHz
From regular observations of the Meridian-2 UHF downlink, it has been noted that during the satellites ascent out to apogee, the transponder is activated when the satellite reaches about 61 degrees North, it then continues to transmit out to apogee, and on its descending leg, until around 36 degrees North when the transponder turns off. A good variety of traffic has been heard relayed through the satellite, including radio station 'studio to transmitter' links, Air Traffic Control centres, and various FM communications links.
The Russian Molniya series of UHF / C-band spacecraft have for some reason not been studied in great detail as far as the radio transmitters go. xBr and pjm spent several hours trying to identify the signals from Molniya after Internet searches simply revealed that they use a "0.8GHz / 1.0GHz" transponder. It has been determined that the downlink transponder runs from 991 MHz to 1001 MHz and transmits RHCP. Please also see the C-Band page which includes some details about the Molniya C-Band downlinks.
Satellite and space aficionado Sven Grahn has a page about his experiments with Molniya reception, here.
The picture below shows the basic design for a 1GHz LHCP helical that is suitable to feed a dish antenna for RHCP Molniya reception. You'll need to make a supporting arm to hold the actual helix, as having it dangling in free space isn't pretty. (see picture below). The ground plane for the helical can be a tin lid of about 30cm diameter.
Since many of the Molniya 1- and 3- series have been monitored, the table below shows the operational status of each of the recent satellites:
Satellite Name Status Frequency band Molniya 3-53 OK C-band Molniya 3-51 No signals - Molniya 3-50 TBA - Molniya 1-89 No signals - Molniya 1-90 OK UHF (possible local scatter from 1-92) Molniya 1-91 OK UHF (Strong DSSS 990.6MHz Molniya 1-92 TBA - Molniya 1-93 OK UHF (1000.45 and 992.45)
The current list of frequencies found to be active is as follows:
Molniya 1-91, 1-90, 1-89 Freq MHz Modulation Comment 991.083 DSSS 490KHz wide 992.443 Mux / Multi carrier tt&c? 994.306 PSK (New 19/09/2006 Molniya 1-91 possibly) 996.013 framed PSK 996.037 2PSK 996.133 PSK 996.193 PSK 996.313 PSK 996.373 2PSK 996.413 PSK 996.533 PSK 996.593 PSK 996.653 2PSK 996.785 PSK 997.033 2PSK 999.775 Framed PSK (New 19/09/2006 Molniya 1-91 possibly) 1000.444 Mux / Multi carrier tt&c?
(above) Molniya PSK downlinks.
Molniya 1-92 992.454 Mux / Multi carrier tt&c? 1000.450 Mux / Multi carrier tt&c?
The FFT's below show plots of the strong 'telemetry' that was observed from each satellite.
(above) 1000.450 MHz - this set of carriers also includes two sweeping tone sets. (click the picture to hear how it sounds)
(above) DSSS signal from Molniya 1-90 centred on 991.083 MHz
(above) A typical cut-over from Molniya 1-91 and Molniya 1-90 - centred on 996.412MHz. Interesting is that the signals increase about 10dB for 1 minute before the cut over occurs. This is presumable to allow the PLL's that are locked to these PSK streams to re-capture the signals ready for the swap to new lower frequency streams.