December 20, 2013 will be the 11th birthday of the amateur radio satellite SO-50.
Now known as SO-50, Saudisat 1C is a Saudi Arabian satellite about 25 cm cubed that was launched by a Dnepr rocket from Baikonur in Kazakhstan at 17:00 UT on December 20, 2002. SO-50 features a “Mode J” FM amateur repeater operating on a 145.850 MHz uplink and a 436.795 MHz (+/- 9 kHz Doppler shift) downlink.
“Most hams already own the necessary equipment to work SO-50,” reports Clint Bradford, K6LCS, who maintains a Web site work-sat.com devoted to working amateur satellites with minimal equipment.
“It is preferable to work SO-50 in true, full-duplex mode – so you can hear the downlink as you transmit. This means – for most – using a second radio or the Kenwood TH-D72A and its true full-duplex capability. The new Puxing PX-UV973 is currently being tested in this mode, too, to see how it works on the satellites.”
SO-50’s repeater is available to amateurs worldwide, and it uses a 67.0 Hz CTCSS (PL) tone on the uplink. SO-50 also has a 10 minute timer that must be armed before use. If you know the satellite is there – but there is nothing heard – you may need to shoot it a CTCSS (PL) tone of 74.4 Hz to turn it ON!
The repeater consists of a miniature VHF receiver with sensitivity of -124 dBm, with an IF bandwidth of 15 kHz. The receive antenna is a 1/4 wave vertical mounted in the top corner of the spacecraft. Its UHF transmitter is a mere 250 mW, and downlink antenna is a 1/4 wave mounted in the bottom corner of the spacecraft and canted at 45 degrees inward.
“Hams just with Technician licenses [or UK Foundation] can work the satellite,” Clint continues. “We are talking about weak signals from 500 miles away – so improving both your TX and RX antennas is critical for success on this satellite.” Plans for making tape measure beams and other inexpensive, high-gain antennas is also on his Web site.
“Do not forget to accommodate for the Doppler shift (+/-9 kHz) on the 436 MHz receive side.”
Complete details – including frequency chart and sources for knowing when the satellite will be over your area, are also on Clint’s Web site.
Watch a video of Simon 2E0HTS working via SO-50 at
Satellite Tracking https://amsat-uk.org/beginners/satellite-tracking/