FM Satellites for Radio Amateurs

FM Satellites for Radio Amateurs

FM satellites are Low Earth Orbit (LEO) satellites orbiting the earth having voice transponders which have uplink on one frequency and downlink on another frequency. They could be V/U with uplink on VHF and downlink on UHF or U/V with uplink on UHF and downlink on VHF. Uplink is the frequency on which the amateur radio operator transmits and the satellite transponder receives. The audio is extracted by the satellite FM transponder and transmitted on the downlink frequency which the amateur radio operator on the earth listens.

So a dual band radio which is full duplex, capable of transmitting and receiving simultaneously like the satellite transponder is ideal for FM satellite operations. One VFO is tuned to the uplink frequency and other VFO tuned to downlink frequency. Another option is to have two separate radios and antennas, one each for VHF and UHF. Dual band antenna or two single band antennas with diplexer can be used for a single radio.

What I usually do is watch the Argentinian Amsat webpage whenever I am free and take frequencies from the live display for Doppler tracking. But if there is no post in the local LEO satellite group at that time, sometimes it may be a waste of time as well because there will be no one to hear your call! FM satellites to look for on the Amsat page are: ARISS, TEVEL series, LILAC, SO-50, AO-91, PO-101. ARISS stands for Amateur Radio on International Space Station. TEVEL series has 8 satellites of which TEVEL 1 and TEVEL 8 are non-functional. Remaining satellites in the TEVEL series gets activated intermittently for a period of 72 hours each time. The webpage by DF2ET tells you which all TEVEL satellites are active at a given time. That page will also tell you if LILAC and PO-101 are active.

LILAC is active three days a week as per a schedule. It is active for 24 hours at a time, starting around 2200 UTC on Mondays, Wednesdays, and Fridays. But with the DF2ET page tracking the activations, there is no need to bother about the schedule, just check that page. Don’t forget to refresh the page each time you access it or else you might see an old set of active satellites. Please note that AO-91 will not work at night as its battery is weak and needs illumination of solar panels. AO-91 and PO-101 are U/V satellites while the rest are V/U.

UVSQ-Sat and INSPIRE-Sat7 are activated only occasionally for a period of 10 hours or so, which will be posted on their Twitter page. But that is a very rare occurrence!

LAPAN or IO-86 is another satellite which can be accessed occasionally from Southern most region of VU land as it has an equatorial orbit. But the FM transponder is seldom active while it is near VU land. It is typically activated over the weekends while over Brazil and is marked as ‘Voice Repeater (Brazil)’ in the schedule published on their Twitter page. VR HT Only India-Indonesia is also seen in the schedule sometimes. But when I checked the activation timing once, it was just after the pass in my region. Some VU Hams operating South of my region have been able to access the voice transponder earlier. But I have never been able to try this satellite.

Here is a chart of the nominal uplink and downlink frequencies of accessible FM satellites in VU region. Doppler correction is needed during the pass. Some need CTCSS tone on uplink for access. SO-50 needs intial activation of 10 min timer with 74.4 Hz tone on carrier for 2 seconds. Once activated, it is accessible with 67 Hz tone on uplink for a period of 10 minutes. PO-101 needs 141.3 Hz tone on uplink. I routinely check the Argentinian Amsat website and N2YO website for pass timings and directions. AMSAT Live OSCAR Satellite Status Page is also useful to know recent activity of the satellites. Links to all the pages discussed is available on my blog, the link to which is available in the description box of the video.

Doppler correction is needed during the pass. Activate SO-50 with 74.4 Hz