HF Radio Experiments

About two years ago, I bought a Raspberry Pi computer.  My intent was to use it for ham radio, among other things.  My favorite ham radio program is FLDigi.  Alas, no matter what tweaks I tried (overclocking, tweaking the FLDigi config, killing off every unneeded process, etc), the Pi just didn’t have enough horsepower to run FLDigi properly.  It would transmit ok, but decoding was choppy and sporadic, at best.  So the Pi got used for other things, like the GPS tracker I took to England, as well as some ham packet radio projects.  About six months ago, I bought a Beaglebone Black.  The BBB is similar in concept to the Pi (ie, a very tiny Linux computer the size of a credit card), but packs quite a lot more CPU power into the same space.  I loved the BBB so much that I bought two more (they’re dirt cheap) and have used them for tons of things (a GPS-driven network NTP server and an ultra-tiny Kali Linux box for pentesting).  I always wanted to try the radio thing again, but I was just too dang busy.  Until this week.

About a week ago, I “built” the stack below.  It’s a BBB (the white box on the bottom), a SignaLink USB (a radio “modem”, for lack of a better term), and a USB hub all rubber-banded together.  The USB hub ties together the BBB, the SignaLink, the serial cable to control the radio, and a tiny N Wifi dongle.  I then had to go clean up the BBB config and install the right software.  The BBB comes out of the box running Debian Linux (which is fantastic), but running a ludicrous amount of unnecessary cruft that bogs it down.  Do you really need a remote desktop server, a web server, and an X server all running on a tiny computer?  Sure, it’s impressive, but if you’ve got ssh access, why in God’s name would you try to choke the box down like that?  A quick bit of cleanup in /etc/init.d/ fixed all that.  I installed FLDigi and Xvfb (a virtual X server, as FLDigi won’t run headless), as well as the FLDigi ruby gem I wrote a while back, and fired it up.  It encoded and decoded flawlessly.  Now I was in business.

I loaded up the truck and headed for the hills.  My goal was to get at least 25 miles away and do some testing back to my home system.  I wanted to try NVIS with the PSK modes.  I brought my FT-817, an auto-tuner, a 1/2 G5RV to string through the brush, my mac laptop, my new Christmas generator, and of course my Rubber-Banded Wonder to control it all.  I also brought my cell phone and a keyboard so I could ssh back into my home system to send and receive data from my home radio.  And of course, about a mile of cables to hook it all together.

So here’s a screen capture from my phone.  I did tests on 80m, 40m, and 20m with BPSK31, BPSK63, BPSK125, as well as QPSK31, QPSK63, and QPSK125.  As predicted, the only band open for NVIS was 40m (it was daytime).  No connectivity on any other band.  BPSK31, QPSK31, and QPSK63 all provided essentially perfect copy, with BPSK63 providing about 70% copy.  No joy with BPSK125/QPSK125.  I was impressed it worked at all with 5W and an antenna cut for the wrong band about four feet off the ground.  But I did manage to prove to myself that PSK NVIS comms at very low power with extremely compromised antennas is actually entirely feasible.  This bodes well for emergency comms use while camping in the Cascades while well out of cell and repeater range.  With temperatures in the 20s, I finally gave up, packed up, and came home.  It was too cold to type.  My fingers actually hurt from the cold.  See the light in the photo above?  That wasn’t so I could see.  It was to put my hands under to warm them up.  I actually found that sticking them in the generator exhaust was more effective (though stinky).  Speaking of the generator, it’s the most amazing thing.  It was sitting next to the truck about three feet from me (see photo), and was quiet enough that I could talk on the radio (and hear it) with no problem whatsoever.  Love that thing.  My big generator is louder 100 yards away than this one is at your feet.

Here’s my view while playing radio.

And here’s where I was parked.



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