how not to be seen

With apologies to Monty Python.

While I’m not Mr. B. J. Smegma, I want to build another Desert Machine that I can place somewhere in the local desert.

Ok, so what’s a Desert Machine?

A long time ago, the original Desert Machine was conceived of, designed, built, tested, and placed out in the Mojave Desert by a group of us, some place in the Mid Hills / New York mountains area, next to an abandoned mine.

A simple box, consisting of a crystal-controlled 40-m transmitter producing maybe 1 W, connected to a “found” abandoned phone line wire strung along multiple decayed telephone poles, aligned in a row more or less allowing the transmitter to feed the NE end of the wire and the SW end of the wire pointing toward LA. A really simple telemetry circuit made of a pair of 555 timers, with one using a thermistor in the timing RC circuit, created a device that would wake up every ~30 minutes, send 10 dahs at a 5 wpm (or so) rate, and then return to sleep.

The timing between the dahs was based upon the ambient temperature; a little math at the receiving end would allow us monitoring the channel (something like 7043.0 MHz) to calculate the temperature at the box. It was loads of fun. Of course, this is completely against Part 97 rules, no ID, no person at the controls, etc., but it was super-cool to be able to tune in on the frequency back in LA, and if conditions were decent, be able to hear the transmission.

It turned out to be about 27 minutes between transmissions, and that drifted slowly over temperature. The crystal transmitter didn’t control the frequency too well; each dah was more of a doo-weep as the transmit frequency shifted a hundred Hz or so during the dah.

The whole thing was powered from a pair of 6 V lantern batteries (the carbon-zinc kind) and housed in some kind of plastic box that was reasonably closed.

Most surprisingly, the whole shebang lasted for about 6 months, growing steadily fainter and chirping worse and worse, until it was no longer hearable.

The device, in a pretty remote and obscure location, was not tampered with. The device was recovered eventually. Some kind of field mouse had built a home inside one of the compartments. The wire was left in place.

Now, how to do something similar but using a solar panel so that the battery lifetime issue is minimized?

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.