ISS Repeater Tips

Miles Mann WF1F has published these tips on how to use the ISS 70cm to 2 metre FM repeater.

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

What is a Cross Band Repeater:

The Kenwood D700 on ISS supports several modes, including a mode called Cross Band Repeating. It allows signals on one band (70cm 437.800) to be received and simultaneously transmitted on another band (145.800 in this example). This combination is called Mode B in the satellite world.

When the radio is in this mode, Terrestrial stations can talk to other ham using most standard dual band FM transceivers, just like using a Mono-Band FM Repeater.
Since the Repeater is 220 miles altitude, it will have much greater range than a typical terrestrial repeater, up to 1400 miles in distance.

When is the Cross band Repeater turned on:

There is no set schedule. Most of it depends on access to the ISS crews. If there a slight gap in the crew schedule we can sometimes get the Repeater Mode turned on. It should be noted that the radio has not been modified for operations in Zero Gravity. All electronics run hotter inside the Space Station. The Cross Band repeater modes does put more thermal stress on the radio than other modes.

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 shift 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
--------------end of pass----------------------

What do I need for Hardware:

Repeaters contacts can be made with a true dual band FM transceiver and Zero Gain antennas or better. Always keep you transmitter power to a minimum. An All mode system with true full-Duplex works the best. Just make sure you have your headphones on, to reduce the Feed back loop.

Azimuth and elevation beam antennas, will of course work the best.

The D700 will typically be running 10 watts while in cross band mode.

You do not need any CTCSS tones to access the ISS Repeater. The repeater is very sensitive to Audio levels. Keep your microphone audio levels turned down Low. If you do not have a Level adjustment, make sure you speak softly. Loud audio will just turn into pure distortion.

When will ISS be in range of my house:

You will need to do some more research here too.
Either use some web tracking programs such as are on the NASA web page or buy your own tracking program. If you are using your own tracking program, keep the data (KEPS) current. For ISS the data must be less than 2 weeks old.

The Space Stations orbit changes daily, you will need to learn about these predictable changes. Each day the first pass of the day will have shifted by approximately 40 minutes earlier in the day. In a few weeks, the first orbit of the day will be around Midnight local time. The whole orbit cycle of ISS repeats approximately every 8 weeks. You will need to learn how to take advantage of when ISS is in a good position. It may mean that you may have to get out of bed at a strange time for a short Repeater contact.

It is possible to see the Space Station with just your eyes on a good pass. The NASA web pages are a good source of information. From this web page below you can select your city and find out when the Space Station will be visible near your home.

City visibility page: http://spaceflight.nasa.gov/realdata/sightings/

General Tracking information:
http://spaceflight.nasa.gov/realdata/tracking/index.html

ISS QSL:
The ARISS Europe team has posted a QSL address for ISS.
http://www.rac.ca/ariss/oindex.htm#QSL

So spread the world.
73 Miles WF1F
MAREX-MG

New MAREX Web pages:
Check out our future ISS Projects and tips on how to use the Chat room on ISS.
http://www.marexmg.org/

Until we meet again
DOSVIDANIYA Miles WF1F