Listening to the ISS repeater

It’s pretty easy to listen to the amateur radio repeater on the International Space Station (ISS) with a very modest set up. Transmitting and making contacts using the repeater is a little more complex, but not too much.

The ISS repeater downlink (what the repeater transmits on and what we listen to) is 437.800 MHz. Because the ISS is moving across the sky at a pretty good clip, the listening frequency needs to be changed as the ISS goes by to account for Doppler shift. At the start of the pass, because the ISS is moving toward you, the listening frequency needs to be a bit higher, 437.810 MHz. As the ISS goes past, it’s moving away from you so the listening frequency goes down. By the end of the pass, you’re listening at 437.790 MHz.

ISS Downlink frequencies

A table of frequencies to listen to for the ISS repeater downlink
Frequency (MHz)
Start of pass437.810
Mid pass437.800
End of pass437.790

If you program these frequencies into your radio’s memory, it’s easy to step through frequencies during the pass.

My set up is pretty simple. The radio is a Yaesu FTM-3207D, but probably any radio will work. The antenna is a simple dual band mag mount on a side panel from an old computer case that serves as a probably somewhat inadequate ground plane. All of it is about 2m above the ground on a shelf.

A dual band (2m/70cm) mag mount antenna on a metal sheet sitting on a shelf
Dual band mag mount antenna setup for listening to the ISS amateur radio repeater

It’s a pretty simple setup, and I’m kind of surprised it even works. Your mileage may vary depending on your local RF environment. My shack/office is full of electronics and can be a bit on the RF noisy side, but I have no problem hearing repeater activity during ISS passes.

I have the radio set to 437.810 MHz (start of the pass) and when the radio picks up the ISS repeater, there’s suddenly a bunch of activity on the radio. When reception gets static-y, I switch over to the next frequency.

This would probably work for listening to other satellites with FM repeaters, although I haven’t tried that yet.

Repeater work

A few days ago I joined some of the local club members at one of the club’s repeater sites that just happens to be located on top of one of the buildings at work. The two repeater controllers were due for firmware upgrades, but my task was to look at the IRLP node, see if it was still running, find out what it was running, make a copy of the software and get remote access to the machine working. I’ve never done anything with IRLP before, but my job was pretty simple.

The equipment is located in the “penthouse” of a 12 story building that houses all the ventilation equipment for the building, making it a fairly noisy place. The club operates VHF and UHF repeaters each in their own cabinet.

Repeater cabinet
Repeater cabinet
Resonator cavities
Resonator cavities
Resonator cavities
Resonator cavities

The IRLP node was an ancient Dell computer sitting next to the repeater cabinets. After attaching a keyboard and monitor to the box, I found it running Fedora Core 3 and spitting out disk errors to the console. Trying to log in to the computer just caused more disk errors to be spit out. Rebooting confirmed that the disk was dead and unreadable. So much for working on the node. Now the job became one of hardware recovery. Took a bit more effort than I expected, but I was able to pull the hard drive and the IRLP board out of the computer. One of the other club members is going to try to rebuild the node using newer hardware, maybe a Raspberry Pi IRLP node (PiIRLP).

On the way out, I got a couple of pictures of the great view from 12 stories above Charleston. This is looking west towards James Island and West Ashley. You can see the James Island Connector in the background.

Rutledge Tower view
Rutledge Tower view

This is looking east-ish at the rest of the peninsula.

Looking east-ish from atop Rutledge Tower
Looking east-ish from atop Rutledge Tower