Pros and Cons of Tone for Access to Amateur Radio Satellites

Pros and Cons of Tone for Access to Amateur Radio Satellites

Some amateur radio satellites require a CTCSS (also known as PL or Private Line) tone for access, while others do not. The old terminology of Private Line is because it gives some degree of ‘privacy’ in that it cannot be triggered without that tone and is used on some terrestrial FM repeaters as well. Most common CTCSS tone is an audio tone of 67 Hz introduced along with the carrier. It is needed on the uplink for Amateur Radio on International Space Station, Saudisat or SO-50, and AO-91. Please note that AO-91 has uplink on UHF while the other two have uplink on VHF.

SO-50 also needs an initial activation of its 10 minute timer with 74.4 Hz tone on carrier for 2 seconds, before you can access with 67 Hz tone. I do find this additional activation tone an added difficulty in access as many of us in our local LEO Satellite Contact group have not been successful in the initial activation of SO-50. If the satellite is not activated early during the pass in our region, we miss out on a substantial opportunity for contacts through the voice transponder.

So that was the downside of having a CTCSS tone. What about the upside? We have often heard conversations on TEVEL series and LILAC which do not need a CTCSS tone on uplink, seemingly simplex terrestrial contacts picked up by the satellite and passed down on the downlink. This is certainly an interference in amateur radio satellite operations as we have only a short period of time during each pass of a LEO satellite to make contacts. Though one might say that satellite sub band above 145.800 MHz should not be used for simplex terrestrial contacts, it may not always be practised. Moreover, the uplink frequency of LILAC is well below that.

What many of the LEO satellite operators do is to keep a default 67 Hz CTCSS tone programmed on the uplink. Even satellites which do not need a tone on uplink can be accessed with this setting. Problem comes only with initial activation of SO-50 and some satellites with a different tone like PO-101. PO-101 needs 141.3 Hz CTCSS tone on its uplink frequency in UHF. If you are tuning the frequency manually for Doppler correction as I do for my operation from within the shack using my full duplex radio, this is even more of a hinderance. I will have to change the tone to 141.3 Hz if I try to access PO-101. If I forget to change it back to 67 Hz after that, I will end up not being able to trigger AO-91, which is another U/V satellite requiring 67 Hz tone on uplink. Similarly, activating SO-50 has been tough for me as I have to change the CTCSS tone twice during the pass. Moreover, as it is a low power output satellite, I am often unable to get confirmation of activation early during the pass.