The International Space Station has two radios set aside for amateur use. One of them currently is setup to function as an FM crossband repeater. This repeater listens in on 437.800 MHz (UHF) and will repeat whatever it receives on 145.990 MHz (VHF). This allows properly licensed amateur radio operators to have conversations (a QSO in amateur radio lingo) over great distances.

Since the ISS moves so fast there are usually only a few minutes with which you can hear the the radio transmissions. If you observe the map on the computer screen you will see a white circle outlined over North America with ARISS written in the middle. This stands for Amateur Radio on the International Space Station. This circle shows the area that can currently hear the transmissions from the ISS. Those at the outsides of the circle have the weakest signal to work with as from their point of view the ISS is lower on the horizon and thus further away.

One other thing the radio operators have to compensate for is the doppler as the ISS moves towards or away from them. A good example of how the doppler affects the signal is imagine a race car driving past you. As it approaches the tone is higher and as the car begins to get further way from you the tone gets lower. This also happens with radio waves and the higher the frequency the more pronounced the doppler affect is. Thus, you need to compensate for the doppler affect more on the UHF downlink from the ISS.

I am doing this manually to illustrate the technique. The radio has both the A & B side set up in VFO mode (Variable Frequency Oscillator) and the stepping is set to 5 KHZ which is the finest setting this radio has. The recording starts soon after I started hearing voices of other amateur operators and stops soon after I could not hear them anymore. You can notice that the sound get staticky when I am late with an adjustment to the downlink. I usually try and keep the up & downlink to match the computed frequency on the computer screen in the top of the video which is just to the right of the world map. The chart below the map are future satellite passes for the next day or so. The address of the website is: [ Ссылка ]

Since there are a lot of people trying to work most satellites and the time is short the QSOs are usually kept pretty brief. Someone calling might just go "KC1OCA, FN32." This would the call sign KC1OCA and their grid location of FN32. If someone hears they might answer with "KC1OCA" then their call sign & grid and "QSL." The grid locations are an abbreviated version of latitude and longitude. Notice the exchange between K2MIK & K4UI . It starts at 02:27, 9 seconds later with another call in the middle its done. These two operators were approximately 763.021 miles apart!

Equipment used is a Kenwood TM-D710G transceiver (The radio on the ISS is a TM-D710E). For the antenna I used a Nagoya NMO-72 atop a Nagoya GPK-01 ground plane and 15' of LMR240 coax. This is one of the most basic setups you can have and as you can see, still gives nice results!

Occasionally the astronauts will work the radio from their end and respond similarly. An excellent video of this is by astronaut Doug Wheelock (call sign KF5BOC) [ Ссылка ]

73 (best regards) from KC1OCA

Thumbnail courtesy of NASA.

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