A Beginner's Guide to Working the ISS
Crossband Repeater
By Bill Chaikin, KA8VIT
This is a simple tutorial to get you up and working the crossband
repeater aboard the ISS. In order to effectively work the ISS
crossband repeater you need about 25-watts of Effective Radiated Power,
(ERP) and a decent antenna. This means a 25-watt radio with a
unity gain antenna, or 13-watts with an antenna that exhibits 3-db of
gain, and so on.
The ISS crossband repeater uplink is on two meters and the downlink is
on 70 cm. Because the doppler shift on the downlink is quite
noticeable you'll need to make adjustments for this.
The ISS crossband repeater also requires
67 Hz tone on the input to
access the repeater.
There are four steps to get going.
Setting up your radio
Checking a tracking program to see when the ISS will be overhead
Checking the status of the ISS crossband repeater
Making contacts
Setting
Up Your Radio
Set up your radio with five memory channels as shown below:
Memory
Transmit
Frequency (MHz)
Receive
Frequency (MHz)
#1
145.990 - 67
Hz Tone
437.810
#2
145.990 - 67
Hz Tone
437.805
#3
145.990 - 67
Hz Tone
437.800
#4
145.990 - 67
Hz Tone
437.795
#5
145.990 - 67
Hz Tone
437.790
We use the same transmit frequency in each memory as the Doppler
shift on the two-meter uplink is well within the ISS's receiver
passband.
Remember, you'll need about 25-watts of ERP to work the ISS.
Checking
when the ISS will be overhead
There are many good free satellite tracking programs available
online. I personally use ISS
Detector Pro on my Android phone. It is automatically
updated with the latest orbital elements for the different satellites.
Since we are not using Yagi antennas which are being pointed at the ISS
we'll want to look for passes (orbits) which will be 50-degrees or
higher above the horizon.
Here is a list of the passes that fit this critera for the week of:
02-DEC-2024 through
09-DEC-2024.
DATE
START
TIME
END
TIME
MAX
ELE DEGREES
02-DEC-2024
11:26
11:37
51
02-DEC-2024
17:55
18:06
83
03-DEC-2024
17:06
17:17
58
04-DEC-2024
11:25
11:31
59
05-DEC-2024
10:37
10:48
82
05-DEC-2024
17:06
17:17
51
06-DEC-2024
09:48
09:59
46*
06-DEC-2024
16:17
16:23
88
07-DEC-2024
15:28
15:39
53
08-DEC-2024
09:48
09:58
63
09-DEC-2024
08:59
09:09
75
09-DEC-2024
15:28
15:38
57
(ALL TIMES ARE LOCAL)
Checking the Status of the ISS Crossband Repeater
Just because the ISS is going to be overhead doesn't mean the ISS
crossband repeater will be on or useable. The ISS crossband
repeater is turned off for a variety of reasons, including but not
limited to, power budget, EVAs and the docking or undocking of other
spacecraft, etc.
No use in listening if the radios will not be on !
Making
Contacts
The exchange of information on a ISS crossband repeater contact is
usually CALLSIGN and GRID SQUARE. If you don't know
your grid square, you can click on the grid square image below to find
yours.
For example, over here in South Euclid, Ohio, my grid square is EN91.
Find a pass that you want to try and work. For this eample, our
pick is the
first in the list above, 02-DEC-2024 starting at 11:26 am.
At the beginning of the pass start on memory #1. Open the
squelch
all the way. As the ISS comes into range the static will soften
or clear. Since we are waiting for the ISS to reach at least
40-degrees elevation, you probably won't hear anything for the first
couple of
minutes of the pass.
Once you start to hear stations on the ISS crossband repeater you
can try to answer or make a call. As the signals starts to sound
fuzzy, switch back and forth with the next memory. At some point
the next memory will start to sound better. This is due to the
Doppler effect shifting the frequency downward.
As the pass continues, continue to switch back and forth between the
current memory and the next.
Try just listening to a few passes before trying working one.
Feel free to get a hold of me if you run into problems.
A Few of My ISS Crossband Repeater Contacts
This recording has recordings from both sides of the contact. First
mine, the WO5O's.
