How to work FM satellites

Saudisat SO-50

Saudisat SO-50

Simon 2E0HTS has released a video that shows him making contacts via the amateur radio satellite SO-50.

This satellite carries an FM transponder that receives signals on 145.850 MHz and retransmits them on 436.800 MHz (+/- 9 kHz Doppler shift). Operation is a little more complex that some other satellites since the transponder needs to initially be activated by a CTCSS (PL) tone of 74.4 Hz which starts a 10 minute timer and then a 67 Hz tone is used for the contact.

Note: If your radio has selectable FM filters use the wider filter designed for 5 kHz deviation FM which is sometimes referred to as a 25 kHz channel spacing filter.

The order of operation is: (allow for Doppler as necessary):
1) Transmit on 145.850 MHz with a tone of 74.4 Hz to arm the 10 minute timer on board the spacecraft.
2) Now transmit on 145.850 MHz (FM Voice) using 67.0 Hz within the 10 minute window.
3) Sending the 74.4 Hz tone again within the 10 minute window will reset the 10 minute timer.

You can set the memory channels in your handheld as follows:
Ch     TX              RX            CTCSS
1     145.850     Timer Reset 74.4 Hz
2     145.850     436.805       67 Hz
3     145.850     436.800       67 Hz
4     145.850     436.795       67 Hz
5     145.850     436.790       67 Hz
6     145.850     436.785       67 Hz
At the start of the pass tune to 436.805 and then decrease the frequency during the 10+ minute pass.

SO-50’s downlink frequencysometimes appears to jump up in frequency, so be ready to occasionally tune up 5 kHz instead of down 5 kHz when trying to follow the downlink.

Watch Simon 2E0HTS working CT2GOY, F0FVK, SP5XSD & EA6SW/portable 6, via SAUDISAT 1C SO-50

Download the SO-50 leaflet PDF – Getting Started with the FM Satellites

You can read Howard G6LVB’s SO-50 article at

Chertsey Radio Club – Getting started with FM satellites

Satellite Tracking

John Heath G7HIA’s article  ‘Getting started on amateur radio satellites’ can be downloaded from