Geostationary Satellites - 3.6GHz to 4.2GHz sky survey - Nils, pjm
C-band is usually associated with 'old style' satellite TV downlinks, but there are many interesting transmissions to be heard, including Inmarsat communications, old SCPC telephone circuits, many different flavours of satellite modems and of course some TV transmissions. Some of the C-band stuff mentioned on this page comes from the HEO Molniya series of satellites.
The minimum sized dish is about a 1.2m, with a good C-band LNA and down converter. If you can find a crystal controlled converter, the phase noise of the oscillator will be low allowing for narrow band CW signals to be resolved. The picture below shows a typical C-band PLL down converter. There is a good quality oscillator that runs at 1716.6666MHz and is referenced from an internal OCXO. The 1.7GHz signal is amplified, and filtered leaving only the 5150MHz which is used as the local oscillator.
The NF of the converter is pretty high at around 15dB, but this is fronted by a good quality LNA, i.e. something with a noise figure of less than 1dB. The converter needs about +18v to keep in lock.
Pictures below show a typical setup with modified C-band LNB to tap out the 4GHz signal ready to feed to the down converter. Use a cheap LNB from eBay that has a low noise figure, remove the IF and DRO and tap the 4GHz signal out.
Below Danmarks Radio as received via 34.5W @ C-Band:
Below Old Molniya 3-53 C-Band downlinks carrying PSK data:
Below TT&C from Marisat F2 launched in June 1976, it spent its final days providing Internet service to research scientists stationed at the Amundsen-Scott South Pole Station.
Below Intelsat 10-02 used to carry a lot of interesting traffic including numerous analogue FM SCPC phone circuits from the middle east.