Monday, October 4, 2010

2010 AfterBurn Report, Part 1 - Voice

The Black Rock Amateur Radio Association is a year-around resource for Amateur Radio operators in the Black Rock desert. But we'd be kidding ourselves if we didn't admit that Burning Man is the peak of "high season" for us. After all, what other event brings so many people -- and so much interest -- to the Black Rock desert?

So, in the spirit of the AfterBurn reports that Burning Man does after each year's event, we thought we'd write up a BRARA AfterBurn report. We'll do it in two parts: this part deals with our UHF voice repeater while part two will cover digital (APRS) stuff.

Great News: BRARA Gets a Mountaintop!

The great news for BRARA late this summer was that the Bureau of Land Management (BLM) approved our lease application for space on a mountaintop overlooking the Black Rock desert! This meant we were able to move our UHF voice repeater (444.175 MHz, PL 100.0, IRLP node 7249) from beautiful downtown Gerlach to a desolate (and RF quiet!) peak high above our beloved desert playground. I won't bore you with tales of humping a lead-acid battery and solar panel up the hill, but I will say that we now have a solar- and battery-powered mountaintop repeater ... and several very tired and sore BRARA volunteers who moved it there over the course of a very long weekend.

The reason the move up the hill was such great news for us is simple: altitude = range. UHF radio waves travel more or less in a straight line and get cranky when stuff gets between them and their destination -- in other words, they mostly work where there's line-of-sight. As any mountain climber will tell you, your line of sight is a heck of a lot better on top of a 1,000-ft peak than on top of a 50-foot tower.

Indeed, when we tried the repeater out right before Burning Man, it rocked -- it was handheld-friendly (think: less than 5 watts) from locations as far south as Gerlach as as far north as Black Rock Hot Springs (think: 40 miles north of Gerlach).

There Goes the Neighborhood

It rocked, that is, until the circus -- Burning Man -- came to town. To provide communications for the event, Burning Man set up a bunch of (legitimate, licensed, legal) commercial radio repeaters less than five miles away from our quiet mountaintop. Even worse, the Burning Man radio frequencies started a mere 2 MHz away from ours (the input to our repeater is at 449.175 MHz and the Burning Man commercial radios start around 451 MHz.) All that meant that our RF-quiet mountaintop was now a RF-noisy mountaintop. A very RF-noisy mountaintop.

The result of this noisy environment was our repeater started "kerchunking" the Friday before Burning Man. By "kerchunking" I mean that the repeater started randomly keying up but transmitting dead air -- that is, no voice signal -- for anywhere from a few seconds to a few tens of seconds. But of course, it wasn't random: it was caused by our repeater seeing interference near its input frequency and mistaking it for an input signal.

Ain't Nobody's Fault But Our Own

To be clear, this wasn't anybody's fault but our own. Our solar-powered repeater was somewhat hastily designed and pressed into service. It lacked two key things: (1) CTCSS ("PL") tone protection on the input and (2) proper RF input filtering. We actually designed it to have PL input protection but for reasons that are too embarrassing to go into here, it didn't quite work out the way we wanted it to. The result was that, if you keyed up on our repeater input with the proper PL code (100.0 Hz), everything worked great. If you keyed up with no PL code, or the wrong PL code, our repeater still triggered ... but then transmitted dead air. Doh!

We weren't able to add proper PL protection to the input in the 48 hours before the event. But thanks to the support and extraordinary generosity of Bob Nagel, WA6TLW (owner/operator of numerous Nevada voice repeaters and APRS digipeaters), we were able to get some high-quality RF filtering installed on the input to the repeater. This necessitated one more climb up the hill (on the first day of Burning Man, no less) to install the filter. The filtering definitely helped but alas, it did not eliminate the kerchunking problem. Thanks to BC, K7BRD, for hiking up the mountain with me!

But It Still Worked, And We Learned Some Valuable Lessons

Even with the intermittent kerchunking the repeater was still quite usable and got a lot of use during Burning Man. In addition to local users within Black Rock City we heard numerous IRLP calls come in and go out during the event. The phone patch even came in handy a few times as well.

Rest assured, we've learned our lesson, and we will be re-engineering the repeater to have proper PL protection and RF filtering before Burning Man 2011!

73 de Phil, N6TCT

Did you end up making use of the BRARA UHF repeater at Burning Man? Leave us some a comment telling how you used it and what your experience was if so.


  1. I used it Friday & Saturday night. Was able to catch Dr Megavolt thanks to another HAM giving info on his location!

    Thanks for the hard work.


  2. I tried to send an APRS email message early in the week but it wasn't received. Honestly, the remainder of the week I spent on Ranger Radio and didn't even turn on the VHF/UHF rig... I thought that the mountaintop UHF repeater was not going to be available during the event - just wasn't paying attention...

  3. Nice blog post! I knew there was a fill-in digi up there, but didn't realize the voice repeater had made the trek up the hill.