APRS iGate

Setting up a small, low-profile iGate for APRS isn't hard and is great for the system APRS ecosystem. And it doesn't have to cost much!

APRS iGate
Junk storage or an APRS Node? Yes.

We've always had some presence of APRS in our area but it was fairly limited and had even fewer iGates to get data in and out of the internet to get to/from APRS on RF.  2015 or so I set up an APRS node in the garage with a mobile whip on top of a pole on an eve mount to fill in some of the gaps and provide an iGate.  I also beacon from this node which gets out over RF via larger digipeaters around me and hopefully provides some kind of service to the hams around me.

Technically this is a digipeater, it does repeat packets it hears over RF and also transmits APRS-IS stations over to RF.  And since it's an iGate of course it puts stations it hears on RF over onto APRS-IS.  However, I generally still refer to it as an iGate because its antenna is only at about 30 feet HAAT so it's very low profile.  It has a typical 12 mile range according to aprs.fi.

The image looks like a hot mess, and honestly, it is, but it works.  The radio is a well-used HTX-212 2M mobile radio powered from a Supernight (ie: dirt cheap) 12v power supply adjusted to about 13.5v with a Raspberry Pi 3 running Direwolf to control it all.  The cabling is all hand-made and in between Pi and radio is an EasyDigi which handles some of the audio isolation as well as PTT.  I added a simple eave antenna mount, pole, and an NMO ground plane and attached a mobile antenna I wasn't using for an antenna.  I estimate that the whole kit from the box of junk to the antenna is around $150 and could be done cheaper if you already have some of the bits like an extra Pi laying around.

To keep everything in the box cool are two fans which are on a relay and buck circuit shown below.  The relay lets me turn the fans on and off via a GPIO pin on the Pi so that the fans don't run all winter long (basically if the Pi is over 30C, the fans come on) and the buck circuit is to adjust the speed of the fans as them running at 13.5V made them sound like a vacuum cleaner.

Fan voltage controller and relay to trigger from Pi GPIO

More Pictures

Top down view

Above, starting bottom left is a Pi 2B sitting on top of a tupperware container with my audio and PTT harness to the HTX212 sitting under it.  At the rear is an MFJ diplexer so I can throw my GD77 Hotspot onto the decent antenna occasionally.  To the right is the fan relay and buck converter pictured above.  Cheapo Supernight power supply is underneath the fan relay box.

And the eagle-eyed might wonder what the LED hanging off the Pi GPIO is?  That's piblink, which gives me visual status of the Pi.  Is it booted, is it online, are any partitions full, is it overheated, etc.

Audio interface and EZDigi

The top prototype board on the right side goes to a USB sound card, the left side hooks up to the mobile rig.  Nothing real fancy there, originally had the notion of making a very generic interface so that if I switched rigs it'd be pretty easy to just swap the cables on one side and good to go.  Below is a standard EZDigi wired over to the audio interface for audio isolation etc.  Dangling off the EZDigi is the GPIO connector for PTT which connects to the Pi.  These are what's in the fancy red tupperware dish in the pictures above which keeps them isolated from everything else since I didn't have a project box big enough to hold both of them.

Ice adds moar gain

The antenna is mounted on a metal conduit junction box screwed to an L bracket on a pole on a mount on my garage, and yes, those are hand-made groundplane wires, #dealwithit.  An NMO is mounted in the box and a mobile antenna I no longer was using is mounted to that.  It could certainly be better, but like most things in my APRS node, it's cobbled-together junk I already had.

Next Steps

It all honestly works very well, no issues from any of the components.  My only failure has been one HT the finals went out in it.  Not sure if it was a high duty cycle from some packet storms or too hot or just failed over time.  And my power supply died once.  Haven't had any real cable, RFI, etc kind of issues.

I'd love to put the audio and EZDigi into a box and screw them down so they're less janky than sitting in a tupperware dish, I should have made the PTT trigger wire longer, I really should put some ferrite beads on some various things just in case, and it'd be nice to just overall clean up the whole mess so it looks nicer, easier to mess with stuff, and better airflow across all of the contents.