Occasionally, the ISS amateur radio equipment is switched into repeater mode, with uplink at 437.800 MHz and downlink on 145.800 MHz. Most of the time the equipment is in APRS mode (you can hear distintive packet sounds when ISS is overhead). Several amateur radio operators have used it to make contacts over distances hundreds of miles.
ISS repeater works like a local mountaintop repeater (exception doppler effect) but much more crowded. Stations you will hear are from other areas of the country (do not expect ISS crews to join in, but they may if ISS workload permits), and you will hear it since it is extremely busy as it comes overhead. Frequency adjusting per doppler effect, proper microphone technique, and patience seem to be the best efforts when establishing contact.
Success Tips for Using the ISS Voice Repeater
ISS repeater downlink is 145.800 MHz (uplink is 437.800 MHz), which is the normal FM voice.
ISS repeater uplink is 437.800 MHz, which is in the high end of the satellite subband. Not all dualband FM transceivers will transmit on that frequency, Check your transceiver owners manual to make sure you will be able to transmit on the uplink frequency. No CTCSS tone is needed to access the ISS repeater.
Dealing with Doppler is a fact of life for all satellite work. Most hams who have tried to work Mode V/U satellites are used to transmitting on a single frequency and listening on a frequency 5 to 10 KHz above the published downlink frequency, then tuning lower in frequency as the satellite approaches. This is because on a 2-meter uplink frequency Doppler shift is less of a factor-on the order of perhaps 3 kHz. At 70 cm, however, Doppler shift is substantial and can easily exceed the ability of the receiver to capture the downlink signal.
Working through the ISS repeater: