This frequency problem is a very old and touchy subject. Many of the terrestrial bound people who have suggested frequencies for Mir and ISS, prefer to suggest different channels for different parts of the world. My point has always been, that the crews are too busy to keep looking at a tracking computer to know when they should change channels. In space there are no borders. So why do we need to make Radio borders. This is why we at MAREX-NA have always opposed using different public channels for Mir depending on where the space station is located. The primary public channel for Mir 145.985 FM simplex was picked by myself specifically so the crew would not have to change channels. And guess what, it works world wide. One channel, Simplex, Simple and no problems. The STS-93 mission is an example of a frequency selection plan, which did not work. ISS will need to be on a stable frequency, you can not have the crew constantly changing channels as they fly around the world at 17, 500 mph in 92 minutes. New Topic: http://garc.gsfc.nasa.gov/~ariss/SurreyFreq/sld008.htm ISS frequency challenge: The proposed channels for ISS are: 145.8000 down link primary 145.8125 down link backup 145.9900 down link backup Note the odd-ball channel 145.8125, it is a 12.5k channel step. The ISS uplinks proposed are: 144.4900 primary uplink 144.4700 backup uplink 144.4500 backup uplink Now here is the challenge: Try to program the down link channel 145.8125 into a memory channel with ANY one of the Uplink channels. As you will find, 99% of all Amateur Radio 2-meter radio made today can not store that frequency combination into memory. RX TX 145.8125 144.450 145.8125 144.470 145.8125 144.490 Only a few radios which have two VFO can support this combination, however most can not save the combination into a Memory location. Good luck Miles