Welcome VK2RQ's Ham Radio Page
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
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and nodes that are no longer valid.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.
Packet Activity in the Local Area
|7.03717||VK2IO BBS, VK2WL, VK2SX, VK2TT, VK4ALN et al
LSB w 1600/1800 Hz tones: The VK2IO HF BBS is stand-alone, but VK2IO-1 node has connectivity via Internet
|145.175||VK2MB-1, VK2BEN-1 et al
National APRS Frequency, lots of activity
VK2TGB BBS in the Blue Mountains (part-time only)
|147.575||VK2IO-1, VK2AMW-7, VK2DOT-1
VK2IO BBS/VK2IO-1 node is separate instance from VK2IO on HF; links to wider packet network with message forwarding (via RF only, no internet); I can connect from my QTH via VK2AMW-7 node/digipeater
|VK2RAG data regenerator
Reception is too marginal from my QTH, need a better antenna :-) Would then be able to access VK2IO, VK2DOT.
There are some others I will check out listed on Steve VK2KFJ's Packet page, (the info is dated, so some of these systems may not be running anymore)
Channels on the VK2MB Packet Digipeater
On the radio used for packet digipeating at the MWRS club house, the
following channels have been programmed:
Main Channel (default), access VK2IO-1, VK2DOT-1, VK2RQ-7, VK2AMW-7 nodes
VK2RSY beacon (for diagnostics/testing)
Backup port to VK2DOT-1 XRouter
Backup port to VK2IO & VK2TGB BBS systems
Primary APRS frequency in VK
Alternate local packet frequency
Alternate local packet frequency