Category: Amateur Radio

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Revisiting Packet Radio on a Raspberry Pi using Direwolf

It’s been a few years since I last played with Packet Radio on a Raspberry Pi, but I have been playing with the uz7ho soundcard software recently and have some packet APRS via the International Space Station.

Looking back at the Direwolf and ax25 setup I was playing with before, I couldn’t actually remember what the order of commands was to get things started up, despite still having it all still configured and installed on the same Pi that I used before. Assuming ax25 and Direwolf are installed and configured (see here and here), the steps to get ax25 up and running and connected are:

  • Start direwolf with: “direwolf -t 0 -p”
  • Note the /dev/pts/x value it returns on startup
  • Run: “sudo kissattach /dev/pts/1 1” (where /dev/pts/1 matches the same value from direwolf startup)
  • The second 1 is the network name from your axports file, like:

1 KK6DCT-5 19200 255 2 2m packet

Ensure direwolf.conf has the same callsign-ssid value, in my example here, KK6DCT-5

Ensure alsamixer has volume around 3/4 for your audio card

To find what audio card device you’re using, use: “axplay -l”. With a Signalink, this shows up as:

$ aplay -l
**** List of PLAYBACK Hardware Devices ****
card 0: ALSA [bcm2835 ALSA], device 0: bcm2835 ALSA [bcm2835 ALSA]
  Subdevices: 8/8
  Subdevice #0: subdevice #0
  Subdevice #1: subdevice #1
  Subdevice #2: subdevice #2
  Subdevice #3: subdevice #3
  Subdevice #4: subdevice #4
  Subdevice #5: subdevice #5
  Subdevice #6: subdevice #6
  Subdevice #7: subdevice #7
card 0: ALSA [bcm2835 ALSA], device 1: bcm2835 ALSA [bcm2835 IEC958/HDMI]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 1: CODEC [USB Audio CODEC], device 0: USB Audio [USB Audio]
  Subdevices: 0/1
  Subdevice #0: subdevice #0

The Signalink is card 1, subdevice 0, so the corresponding config in direwolf.conf for this device is:

ADEVICE  plughw:1,0

To summarize:

  1. Start direwolf, grab the /dev/pts/x value
  2. Start kissattach with the same /dev/pts/x value
  3. Now you should be able to “call 1 nodename” and get a packet connection out via Direwolf to your radio.

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Packet Radio via the International Space Station – March 2021

The Packet Radio service on the ISS has been out for a few months, but during an EVA yesterday a cable was replaced and the service is back up again for the first time today.

I used my regular 2m radio , an Icom 880h with my homebrew copper wire 2m groundplane antenna in the attic, and transmitted on full power (50w), hooked up to a laptop via a Rigblaster, running UZ7HO soundmodem for the packet radio modem, and used the UISS software to send the APRS packets.

The pass was only 57 degrees at the highest, so it wasn’t a particularly high pass. I don’t think I started to hear packets until it was a couple of mins towards the peak. I heard 6 other stations get digipeated by the ISS: KB6LTY, K6FVC, N6RSX, KG6LHW, W7OSG and AB7DY, and I got about 3 APRS transmission digipeated (my callsign is KK6DCT):

If you’re wondering what this is about I have a couple of other posts from when I tried to get this working a few years ago:

Amateur Radio Packet via the International Space Station (ISS)
Amateur Radio Packet via the International Space Station (update 2)
Success! Packet Radio via the International Space Station
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What I learned in Amateur Radio last week: always re-evaluate your assumptions

Amateur Radio is a hobby that keeps giving, there’s always something new to learn. In the past week I learned some interesting things:

  • don’t take assumptions for granted, question everything: I assumed I had been running my HF radio on 13.8v on my power supply, because that’s what it’s rated at. It has a power out knob on the front, and I’d dialed back the power to 12v a long time back because I plugged in a cable in to the front outputs to power an antenna analyzer. This was a long time back, maybe even a year or so ago. I’d assumed the knob that’s next to front outputs controlled the output just for those front outputs on the front panel, but turns out it controls the outputs for the main high amp outputs on the back running my HF radio too. I only found out by accident because I has plugged the front output into something else this week and wanted to dial back the voltage and my HF radio but out. Huh, that was surprising by know I know I’ve been running my HF radio on less than 13.8v for over a year.
  • I’ve had S9 noise on all backs lower than 20m for as long as I’ve had my HF radio setup, so I few years now. I’d always assumed it was from something in the neighborhood. I normally work 20m or 15m so didn’t think too much of it, and didn’t spend any time to trying and track down the noise source. We’ve had a security camera system that records to hdd for a number of years but recently replaced it with Ring cameras instead. I never bothered to turn off the hdd recording box until last week as it was on a shelf under my desk. All of a sudden, my background noise on 40m dropped from S9 to S1. Huh, well that was easy, why didn’t I try that sooner?
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Using a VT132 for Packet Radio

I have an AEA PK-232 that I picked up a couple of years ago at my Amateur Radio club’s White Elephant sale for a few bucks. With the VT132 that I just recently built, it works as an excellent terminal client to the PK-232.

To connect, set baud rate in the VT132 to 1200 8N1. Connect with a null modem cable. Power on the PK-232 and you should see:

Press type a star (*) for auto-baud routine.

Press * and then you should see the AEA PK-232 startup copyright message.

To get a cmd: prompt to enter commands, press Ctrl-C.

I’ve attached my 2m radio with the audio in so far, and here’s a pic while decoding some APRS messages:

Next I need to make a custom cable to connect to my Icom’s data port, and then I should be all set to work some packet.

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