Chris Kantarjiev
Previous call: KG6VYD

Find me via APRS
This is as much a historical record as it is a "current status"... so bear that in mind as you read through it. I guess I'm a packrat in webpages as well as everywhere else! If you came here because you're interested in building your own digi/igate, there's a cookbook approach over here.


One of the first things I discovered after getting my license was APRS, the Automatic Position Reporting System. If I'd known about APRS sooner, I'd have gotten licensed sooner - it combines a whole bunch of my history. I quickly bought a Pocket Tracker and built it. I hadn't built a kit for a long time, and this is a fairly dense one, so it got me up to speed right quick. I got it going the first time - that was very cool. And then I discovered that a 250mW transmitter doesn't have much of a chance in the SF Bay Area - the noise floor is too high and the terrain too varied to reliably hit the high digipeaters. And at our cabin in southern Yosemite, the digipeaters are too far apart. So I started learning a lot about the APRS digipeater infrastructure, and decided that I needed to build and deploy a couple in the areas where I want to play.

Digipeaters I've initially set up a digipeater in my garage with a MFJ 1270B TNC with a UIDIGI EPROM and a Radio Shack HTX-202. It's configured to be a fill-in digi, intended for WIDE1-1 only (K6DBG-1). This allowed my Pocket Tracker to be heard around my neighborhood - before, it couldn't hit any of the digis in the area. A few other people used it, too. Getting this working required mounting an external antenna - no big surprise there, but I tried to cheat with a mag mount 1/4 wave on top of my tool box. I guess the chicken wire in the stucco was really getting in the way. This digi ultimately went away.

John VE3NEC burned the EPROM for me, which was an adventure in itself - in the post-9/11 world, such things traverse customs very slowly. Scott N1VG has said that he'll do this for a nominal fee for anyone with a TNC2 that wants to set up a new digipeater - no border crossings.

For a while, I had another MFJ 1270B with a PacComm 5.0 EPROM at our mountain cabin (K6DBG-2). There wasn't a digipeater anywhere nearby, so I thought that it made sense to try to run this as a WIDEn-N digi. That turned out not really to be true - there was already too much APRS 'noise' in the air from high-and-wide digis that set their beacon paths too long. In addition, the PacComm code doesn't do real WIDEn-N processing - the setup described above will accept a few WIDEn-N path elements, but just relays them once more without proper processing. Added to that, my location really isn't that good! Splat path analysis says that my HAAT is about -1000' (yes, negative 1000 feet). I heard a lot of traffic, but my beacons didn't get out very well. So I changed configs to be a fill-in (WIDE1-1) digi to try to get signals up to higher digis. I thought it might help someone driving by on CA 41. Putting up a J-pole helped a lot (see below), but the truth is that it's just not a good location.

I ended up reconfiguring that location to be an igate - there were none very close by, either. That was done with a Linksys WRT54G running aprs4r, using a Tracker 2 looking at a weather station...

For grins, I put together a little battery backup for this, consisting of a 7AH gel-cell (sealed lead acid or SLA) battery and an ACI Super Charger (#1206CC). This is a pretty nice charger that will do high-current charge and then taper and finally float as needed. It does 3A, so the station mostly runs off the power from the charger. The switching supply in the charger puts out a fair bit of RF hash, but when I finally moved the antenna outside, that stopped being a problem (it was quieting the receiver when the antenna and charger were only a few feet apart). I bought it from Apex Distribution, who sell them for much less than most other vendors. Unfortunately, once I set up an HF station nearby, I discovered that the charger puts out a lot of hash on 20m, too. I switched to a 5A charger from A&A Engineering, which is RF-quiet.

Ultimately, I'd like to get one of the local repeater operators to mount a digi somewhere really high - my location is far from ideal. Jeff KF6CNV voluteered to let me host some gear at his shack; he's actually up above our little valley, with a view north towards Yosemite, instead of in a hole! So I moved the WR-154 and an X-Digi to his place, configured as fill-in (WIDE1-1) digi - K6DBG-3. (I like the X-Digi a lot better than the TNC2 - smaller package, flash memory to store settings, and much lower current draw. Not as flexible, but doesn't need to be for a dedicated digi. The biggest drawback is that it doesn't have over-the-air sysop access ... so good for a local digi, but not a remote one that may need care and feeding.) It's a definite improvement! It has good line of sight to the igate at K6TJS in Los Banos, and heard my 5W tracker up CA 41 as far as Sugar Pine (past our cabin). Unfortunately, he moved away and we lost access to that location. I'm still looking for a new home; at the moment, there's basically no coverage in Oakhurst.

Tracker settings There are a lot of web sites that have discussions of APRS, either in theory or its history, but don't help the new tracker owner to get started. There are also a lot of example sites that are way out of date, with unresponsive owners. So here is a brief summary of what I've learned, both as a tracker and a digi operator, based in part on the 'New Paradigm' of April 2005:
Be courteous to your fellow APRS channel users:
RELAY, WIDE, TRACE, and TRACEn-N are no longer valid path settings. Please discontinue using these settings and use the new and improved settings.
If your tracker has Smart Beaconing, use it.
If your tracker has MIC-E encoding, use it.
Unless you are launching a balloon, it's probably not worth sending your altitude (and the value from your GPS is probably wrong anyway).
Turn off your vehicle tracker when the vehicle is not in use.
Modern radios can live with a TX delay as short as 100msec, perhaps less. Do some experiments to see how small a value you can use and still have your packets copied. A few hundred milliseconds saved may not seem like much, but it adds up.
If your tracker has 'only send valid', to only send a position when you have a good GPS fix, use it.

Use WIDE1-1,WIDE2-1 as the digipath. If your tracker can alternate between two configurations, use WIDE2-2 as the alternate digipath. For most of the US, two hops will get you into an IGATE. If you're not getting into an IGATE, contact the APRS operators around you to see what digipath they used. You can find stations near you with findu by searching for your ZIP code.

If you think you want to run a digi because you're not getting in to the digis around you - check your path, and check your antenna. If the channel is truly clogged, see if the digis and trackers around you are using overly long paths in their beacons, causing channel congestion. If so, contact the operators and see if they can be convinced to reduce the QRM they're introducing. If that's still not enough, consider setting up a WIDE1-1 "fill-in" digipeater. It only takes about 10dB difference to capture an FM receiver - the fill-in is intended to let your tracker capture someone's attention, without fighting with hidden terminals (other APRS stations that the high-and-wide digipeater can hear but your tracker can't). WA8LMF Steve has a great discussion about digipaths, with pictures!

There's an effort to gather APRS info into the APRS wiki. It's got the basics, and is slowly growing - look there first. There are a lot of broken/old/outdated pages out there with advice that is no longer correct.
Even though it's oriented towards the Pacific Northwet, is one of the best collections of practical and up-to-date APRS operating information. Take a good look there for further reading - especially if you're wondering about the 'why' behind the recommended digipaths above.

If there is one, I suggest that you join your regional ARPS discussion list (such as CA_APRS for California, where you can learn a lot about your local operating environment. You might also want to join the general APRS discussion mailing list at aprssig.

I wanted an igate at our vacation QTH. I don't want a computer with spinning disk, and wanted something that can be easily backed up with a battery. The Linksys WRT54 family of routers, running linux and reflashed with OpenWRT, seems like the right thing. Folks are running digi_ned on it for digipeating.
My WRT54GS (v1.1) consumes about 180mA, despite the 1A power brick rating.

Only certain versions of the hardware (most of them, but be careful) are supported by OpenWRT. has lots of details; I suggest that you make sure that you can reflash your hardware before cracking the case. I used a GS, but there's no reason that you need 802.11g to do this.

digi_ned is a very nice, very flexible digipeater. I wanted an igate, too, but digi_ned doesn't provide that capability. The authors suggest that you should use a separate igate program and plumb the two together with AX.25 sockets.

OK, off to find AX.25 support for the WRT. I ended up using an image from, because it already has AX.25 baked into the kernel. Those images have a bunch of other tools (like X-Wrt) already built in. (If you don't read German, the WRT images with AX.25 are hiding here - based on White Russian 0.9. (But read on ... you probably don't need or want this.)

The first trick is to add serial ports. The board has a blank spot for a 10-pin connector that brings out two serial ports. Ron Whitby has detailed instructions for that here.

BUT! His instructions are for a specific, mismarked version of the AD233BK kit. If you follow them exactly, port 2 won't work. His version had Cts and Rts reversed, so you need to swap those connections if you don't have the same version (and you probably won't). See this note.

Ron's instructions are based on a v1 WRT45GS board. Linksys moved some components around, so the front connector placement he suggests doesn't really work well on later boards. I found this out the hard way, and my front panel is pretty butchered as a result. It will be more work, but I think it makes sense to bring the connectors out the side, as shown here. There are some good notes about using the WRT for ham radio here.

It's really small!
I recently convinced the good folks at CompSys (who make the AD233BK kit) to put together another little board for this purpose. It's shown at this page, look for the STR232A. (You want the 3.3v version for the WRT.) This unit brings out TXD/RXD/GND to a 1/8" stereo jack, so it can be mounted in a simple drilled hole. You then use a small pigtail to connect to a DB9. He has a version that uses an RJ45, as well, if you like that better (harder to mount).

I only wanted to wire up one serial port, but I left room for a second board if I decide I want it later. I drilled a 1/4" hole at more or less the midline. I took a file to the edge of the STR232 board to make it fit the inside of the case - that's not strictly necessary, but it left me with more of the threads sticking out.
One Hole!

There are a few more tricks that are hard to track down, especially regarding the second serial port (/dev/tts/1). The default setting often has the wrong irq associated, so you need the setserial package:

ipkg update
ipkg install setserial
/usr/sbin/setserial /dev/tts/1 irq 3
You may also want stty:
cd /usr/sbin
chmod 755 stty
rm stty.tgz


/usr/sbin/stty -F /dev/tts/0 clocal raw speed 4800
/usr/sbin/stty -F /dev/tts/1 clocal raw speed 4800

It's possible that you will need
 ln -s /lib/  /lib/ 
to get stty to run correctly. Those settings won't survive a reboot, so add them to
and they'll be invoked at boot time! If you use /dev/tts/0, you'll probably want to edit /etc/inittab to disable the login shell there. (I've converted some boxes where /dev/tts/1 just doesn't work; I suspect there's a chipset difference that the driver doesn't handle. Beware.)

Once you've got the hardware up and running, get the digined package with apt-get, as described.
WA7NWP & I are collecting digi_ned wisdom here, including beacon settings and other goodies for the "new paradigm" for digipeaters.

The pre-built version is the cut-down version for "embedded computers". It turns out that this doesn't support things like AX.25 ports, weather stations, or additional serial devices; it talks to directly to a serial TNC with KISS. So much for plumbing to an igate program!

I had also found a WRT-compiled version of aprsd, from Jonathan KE7BAP. (I stashed a version here). It also turns out not to have ax.25 support. In the process of casting around to try to make this work anyway with my Tracker2 KISS TNC, Jim NU0C on the digi_ned Yahoo!Group suggested that there was no inter-program plumbing needed, but that digi_ned and aprsd would happily share the same KISS port. He really meant port, not serial port, though.

Bill WA7NWP said something that got me thinking I could finesse this, using kissattach to turn the TNC into a KISS port, and net2kiss to attach the KISS port to a pty. Much hilarity ensued when I discovered that net2kiss wants BSD-style pty naming, but OpenWRT uses Unix98 pty naming. I learned much more than I wanted to about this whole pty api debacle, and finally discovered that my kernel still supported the legacy pty naming, but didn't make the devices at boot time. With the help of this page and the makedevs program, I was able to make legacy ptys and get net2kiss working. Unfortunately, it then turned out that the aprsd image isn't prepared for a KISS TNC, but only command mode.

APRS4R About this time, I learned about aprs4r, a ground up implementation of a digipeater/igate combination in Ruby, by a group of hams in Germany, with the WRT as a target platform. Micha DO5MC was gracious enough to allow me to beta it, and was very responsive to my bug reports. In only a few days, I had everything I needed configured on my WRT and running solidly! Now I'm up on the 1.0.1 release, which is quite solid. It's based on the Kamikaze release of OpenWRT, and you may want to get the X-WRT version that has a nice webserver console built in from here, although the native Kamikaze web front end (LuCI) is getting pretty usable. I put together a cookbook for building such an igate/digi from scratch.

I have the Tracker2 configured to send out its normal status/voltage beacons, and will eventually hook up some weather gear. Otherwise, it's used as a KISS-mode TNC by aprs4r. It's been deployed as CDRVLY, providing WiFi to the cabin as well as digipeating and igate services to the surrounding area. Now I'm spending some effort trying to find other sites in the area...

Back to my amateur radio page.

Last updated Dec 27 2009 by cak