Yesterday I participated in what has become an annual event, a mobile field-day where radio amateurs in the district drive around in the countryside and make radio contacts on HF, mainly 80m (3.5MHz), as well as on the higher bands. Some of the participants stop on the side of the road and put up temporary antennas, usually low-hanging dipoles for NVIS, others have antennas mounted on the car. This was the third time I participated, and the first time I had an HF-antenna mounted to my car. The organizing team put up a reference station, with the call sign LA1G/P, for comparing antenna systems and radio coverage, as well as serving as a final destination for the trip to meet up and have a chat with other people. This year, like previously, the reference station was set up in the parking lot at Vindfjelltunet.
My car, a ’98 VW Golf Mk4, did not have any trouble with a 100W strong RF field emitted from a “magmounted” antenna on top of the roof. However, there were some quite strong RF noise coming from the car electronics. I did not have time to investigate, it could possibly be solved with the usual EMC tactics of ferrite cores on cables and so on, so for working the weaker contacts I simply turned off the ignition.
During the 180km trip, I made 4 check-ins with the reference station, as well as some contacts with other participating mobile stations. The map shows received (R) and sent (S) signal reports and the distance to the reference station for each check-in.
My “shack power supply”, a Palstar SPS8250, is providing me with 13.8V at up to about 25A for various pieces of radio equipment. It is mostly running with a very low load, 1-2A, and don’t really need the active cooling of a fan. Since the fan is a bit noisy, I made a simple thermostat so that the fan could stay mostly off and only go to full speed at high load and temperature. It is really simple, with an AVR and a few bits of C code to read an LM335A temperature sensor through the ADC and then simply switch the fan through a FET. Two potentiometers are also read through the ADCs to supply high and a low thresholds for the hysteresis. In the picture above, you can see the crude veroboard bolted to the fan in the back of the power supply. The two trimmers are at the bottom, just behind three Berg pins; one connected to ground and the other two to the wipers. This way the thresholds can be read simply by a voltmeter and some basic arithmetic (0-5V = 0-100°C). The LM335A can be seen wrapped in heat-shrink tubing and glued to the heat sink. Except for that I run the whole thing off a supplied fan connector on the main PCB, which apparently has some kind of built-in speed limiting for the fan, it works fairly well. I have it set with about 50°C and 35°C as the high and low thresholds. See full source code at github: avr-thermostat and my ugly schematics/working notes below.
I’ve created a public calendar for the amateur radio Nordic Activity Contests on VHF/UHF/SHF. The regular Tuesdays and Thursdays are set to auto-repeat, but the fifth Tuesdays are updated manually (for now, about a year into the future).
Get it as a stand-alone HTML page, in XML (probably the best if you want to add it to your own Google Calendar), iCalendar (for almost all calendar applications) or embed it in your own site.