ISS Repeater Tips.

How to use the ISS Cross Band Repeater
By Miles Mann WF1F
MAREX-MG (Manned Amateur Radio Experiment, North American Division)


What Frequencies do I use:
The Cross Band repeater mode listens on 437.800 MHz FM, and will Transmit on 145.800 MHz FM. You will need to compensate for Doppler, especially on the Uplink side 437.800. On the 2-meter band 145.800, if you can not compensate for Doppler, do not worry about it. Most of the time you will be able to hear the down link signal fine. The Doppler on 145.800 is only 3.6 kHz maximum. Your stock FM receiver will still be able to hear ISS when it is 3khz off frequency.
The 437.800 uplink is a completely different story.
You will need to compensate for Doppler, every minute of the pass. If your radio has only a 5khz you will need to time your transmissions for when your Doppler error is less than 3khz different from you calculated uplink frequency. The closer your uplink frequency matches the receiver’s frequency on the repeater, the stronger you signal will be into the repeater.
For All mode Users. If you can pre save these split frequencies in to memory channels that will make life much easier during the short 10 minute ISS pass window.
For VFO users, this chart will help you sweep across the 70cm band and will help you stay on the correct uplink frequency.
Down RX Up TX
1 145.803 437.790
2 145.803 437.793
3 145.802 437.795
4 145.801 437.798
5 145.800 437.800
6 145.799 437.803
7 145.798 437.805
8 145.797 437.807
9 145.797 437.810

For users with Radio designed for 5 kHz channels steps, program in the following channel splits.
Down RX Up TX
1 145.800 437.790
2 145.800 437.795
3 145.800 437.800
4 145.800 437.805
5 145.800 437.810
How to I calculate Doppler:

Most satellite tracking programs will calculate the Doppler frequency error for a satellite. Here is an example from InstaTrack. I assigned the satellite ISS, the radio frequency of 437.800. The display reports will now show me the approximate Doppler error for a given time.
In this example, at 22:06 UTC time, the ISS will be in range of my location and the Doppler on 437.800 will be +10,240 Hz. In order for my signal to line up with the receiver, I need to transmit 10,240 Hz LOWER in frequency to compensate for Doppler + Positive shit in my frequency (Due to the 17,500 mile per hour speed of the Space Station).
So instead of transmitting on 437.800, I will transmit on 437.790.
Here is an example of a typical
3. ISS (ZARYA)
UTC Date Time Azim/Elev Range Doppler
03Feb2008 2206 237/ 4 1748 +10,240
03Feb2008 2207 238/ 9 1372 +10,182
03Feb2008 2208 238/ 16 1002 +10,002
03Feb2008 2209 240/ 30 652 +9,448
03Feb2008 2210 250/ 64 387 +7,184
03Feb2008 2211 47/ 55 420 -897
03Feb2008 2212 53/ 27 711 -7,876
03Feb2008 2213 55/ 15 1066 -9,600
03Feb2008 2214 55/ 8 1438 -10,046
03Feb2008 2214 56/ 3 1815 -10,195
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