May 162011
 

This weekend just gone I was at Imbil helping out with the International Rally of Queensland, reporting scores for the car rally there.  This was my first look at packet radio in action.  Prior to this I had enabled the amateur radio options in the kernels I built, but never tried actually hooking radio to computer.  I shall be posting some notes on how I got this working…

zhouman ~ # uname -a
Linux zhouman 2.6.35.7-lm2f-nb #2 Wed Oct 13 00:42:58 EST 2010 mips64 ICT Loongson-2 V0.3 FPU V0.1 lemote-yeeloong-2f-8.9inches GNU/Linux
zhouman ~ # ifconfig sm0
sm0 Link encap:AMPR AX.25 HWaddr VK4MSL
inet addr:172.31.32.1 Bcast:172.31.32.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:256 Metric:1
RX packets:365 errors:0 dropped:0 overruns:0 frame:0
TX packets:36 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:10
RX bytes:24236 (23.6 KiB) TX bytes:6850 (6.6 KiB)

zhouman ~ # mheard
Callsign Port Packets Last Heard
VK4EA-9 sm0 6 Mon May 16 17:59:12
VK4NRL-9 sm0 1 Mon May 16 17:58:40
VK4VP-1 sm0 8 Mon May 16 17:58:38
VK4RAI-3 sm0 9 Mon May 16 17:57:58
VK4TIM-9 sm0 14 Mon May 16 17:57:56
VK4TDI-1 sm0 2 Mon May 16 17:57:39
VK4DC-1 sm0 15 Mon May 16 17:57:07
VK4TEC-9 sm0 120 Mon May 16 17:56:08
VK4FY-1 sm0 18 Mon May 16 17:54:38
VK4RMO-3 sm0 1 Mon May 16 17:54:33
VK4RGC-3 sm0 3 Mon May 16 17:52:48
VK4RC-1 sm0 8 Mon May 16 17:51:29
VK4FIL-1 sm0 4 Mon May 16 17:46:44
VK4RIL-13 sm0 4 Mon May 16 17:45:43
VK4RBR-3 sm0 5 Mon May 16 17:42:59
VK2RDO-3 sm0 2 Mon May 16 17:41:19
VK4RRC-13 sm0 3 Mon May 16 17:36:39
VK2JUB-1 sm0 2 Mon May 16 17:34:44
VK4BNQ-1 sm0 1 Mon May 16 17:26:58
VK4LDA-9 sm0 2 Mon May 16 17:24:59
VK2POO-9 sm0 9 Mon May 16 17:21:24
VK2XFL-9 sm0 1 Mon May 16 17:21:09
VK4RSR-3 sm0 1 Mon May 16 17:20:04
VK4IE sm0 1 Mon May 16 17:15:04
VK4ALJ-3 sm0 1 Mon May 16 17:15:00
VK4HPW-9 sm0 5 Mon May 16 17:13:23
zhouman ~ #

Set-up consisted of:
Linux kernel on Lemote Yeeloong, latest soundmodem driver, Yaesu FT-897D, homebrew interface cable plugged into Yeeloong’s onboard sound card, USB serial driving BC547 in interface cable for PTT.

zhouman ~ # cat /etc/ax25/soundmodem.conf
<?xml version="1.0"?>
<modem>
<configuration name="FT897-D">
<chaccess txdelay="150" slottime="100" ppersist="40" fulldup="0" txtail="10"/>
<audio type="alsa" device="plughw:0,0" halfdup="0" capturechannelmode="Mono"/>
<ptt file="/dev/ttyUSB0"/>
<channel name="Channel 0">
<mod mode="afsk" bps="1200" f0="1200" f1="2200" diffenc="1"/>
<demod mode="afsk" bps="1200" f0="1200" f1="2200" diffdec="1"/>
<pkt mode="MKISS" ifname="sm0" hwaddr="VK4MSL" ip="172.31.32.1" netmask="255.255.255.0" broadcast="172.31.32.255"/>
</channel>
</configuration>
</modem>
zhouman ~ #

I’ve shut it down for now, but I’ll give it a bit more work on 145.175MHz tomorrow. Once I get something working, I might set something up using the O2 or one of the Fulongs (probably the latter) and see about getting soundmodem back into Gentoo.

Update: After hand-editing the ebuild to enable APRS support, I can successfully report that not only is soundmodem working, but so is Xastir on my Yeeloong, as can be seen on aprs.fi.

  2 Responses to “Experiments with AX.25”

  1. What about IPv6? 🙁

    • IPv6 over AX.25 would be good, but remember that it at best runs at 9600 baud. IPv6 requires a MTU of 1280 bytes, which would take a second (1.066 sec to be exact) to transmit on 9600 baud packet.

      In this case I was on the 2m band, thus using 1200 baud packet. So it would be slower again… try about 8.533 sec.

      I only put in an IPv4 address purely and simply to get the interface up, I was more interested in the raw AX.25 traffic such as APRS. Packet is useful for very short messages, but it’s much too slow for IP traffic of any kind IMO.

      That said… I do see a future with IPv6, using transverters to move 802.11b/g equipment onto one of the microwave amateur bands (1296MHz, 5GHz or 10GHz for example) to form a high-speed packet backbone which could be used for things like IRLP and EchoLink as well as emergency comms.