At my local radio club, one of the members likes to hop on the 80 metre band with his morse code key. We were discussing what might be some good topics for upcoming lectures, and he mentioned that he was curious about beverage antennas.

I didn’t know anthing about this topic, so I thought it would be great to go away, do some research and learn about them so I could deliver a lecture. It seems indeed that beverage antennas are a great option for receiving signals on the low bands, but they do require a huge amount of space, and are less well suited at a transmissing antenna.

At my local amateur radio club I gave a talk about packet radio, covering topics such as AX25 frames, digipeaters, netrom nodes, and applications that run over packet radio such as APRS and BBS. On YouTube you can find a recording of the talk .

The slides from the talk can be found here:

AX.25 Packet on Linux

Recently I have been experimenting with setting up packet radio on an ASUS netbook running Debian Linux. There have been a few challenges with this, which I describe below.

• Installation of AX25 Lib/Tools/Apps: the problem here is that the packages supplied with debian are a little old, and assume that the kernel has support for legacy BSD-style pseudo-terminals. However, in the standard kernel distributed with debian linux, support for the legacy ptys has not been compiled in. So, I had a choice of recompiling the kernel to support the legacy ptys, or else compile up newer versions of the ax25libs/tools/apps that support the new Unix98-style ptys. I chose the latter.
• The AX.25 “call” program supplied in the ax25apps package was crashing when I resized the window, and didn’t have support for any scrollback buffer. I found a patch on the web that addresses these issues, but it was built against ax25-apps-0.0.8-rc2, and wouldn’t apply cleanly to the more recent version of call.c in CVS that supports the Unix98 PTYs. So, I updated the patch to make it compatible with the newer release, and you can download the updated patch here .
• I had an issue with getting linux soundmodem to work at 300 baud. I found the fix was to use modem tones less than 4*300=1200 Hz. However, I wanted to cover the national APRS freqnency on 40 m and the frequency used by our local packet group around 1 kHz higher together at the same time with the same radio. I found a testing patch against soundmodem-0.16 that removes this restriction on the modem tones.
• The aprsd packaged with debian doesn’t support multiple TNCs, and you can only run one instance of it on the system. So, I looked to the APRX daemon instead. This does support multiple TNCs, but unfortunately kept dumping core on my system. I made a small patch to prevent this from happening.
• I found a patch to provide Internode Protocol (INP3) Support for Linux on this page . However, the patch was written against linux kernel 2.6.4, and does not apply cleanly to the latest 2.6.32 kernel. So, I updated the patch . However, I found that the patch causes a soft lockup when taking an AX25 interface out of service, due to a deadlock with the spin_locks, so some additional work is needed to address this. Investigations so far indicate a problem with nr_del_node_found(), which removes neighbours and nodes that are no longer valid. When it is called, sometimes there is already a lock on the global neighbour list, and sometimes there is also a lock on the global node list. When removing a neighbours or node, an attempt will be made to acquire a lock on the global neighbour or node list, and if such a lock is already existing, there is a deadlock, and the CPU will just spin. Will need to think about the best way to clean up the code.

Packet Radio Resources

I have collected here some useful links in my search to learn about packet radio.

CSQ Summary

The following is a proposal from Bruce Prior N7RR for a signal reporting system based on Copyability-Strength-Quality (CSQ) , and as an alternative to the traditional Readability-Strength-Tone (RST) system.

C or Copyability

\(^{*}\) For Copyability reports of N and 0, no Signal Strength or Quality reports are needed.

Having had my Elecraft KX3 ultra-portable radio for a few months now, I felt it was high time to take it out into the field. In particular I was curious to see how it would perform with my Alexloop magnetic loop antenna. This antenna covers 40m-10m, and while it clearly isn’t going to compete against a dipole, it is very quick and easy to set up, and should normally give reasonable performance on the higher bands at least.