One of the most fun parts of being a ham is utilizing the VHF/UHF crossband repeater onboard the International Space Station. Hams often make QSOs, or contacts, off the repeater, and occasionally speak with the astronauts onboard. This repeater operates uplink at 145.990MHz (2m ham band) and downlink at 437.800MHz (70cm band).

Much like an ambulance siren sounding higher in tone when it moves towards you, and lower when it moves away, we get a Doppler shift from the ISS. Because of the incredible speeds relative to us, we must account for this Doppler shift. As Doppler effects are frequency dependent, this is especially important for receiving at 70cm.

Surprisingly, it doesn't take much to hit this repeater. I first hit the repeater with only a $20 Baofeng and a 3 element yagi made from a tape measure. Since then, we've used Apollo, the 0.5m telescope at the Sommers-Bausch Observatory to piggyback our full-duplexer Arrow yagi with a Kenwood D-72 full duplexer HT. We 3d printed mounting bracket to attach to the Losmandy bar.