[amsat-bb] ISS Repeater Tips.

MM ka1rrw at yahoo.com
Sun Feb 3 13:45:33 PST 2008

ISS Amateur Radio Status: February 3, 2008
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
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 
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

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

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

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. 

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

The ARISS Europe team has posted a QSL address for

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.

Until we meet again

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