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Friday, April 10, 2009

Parachutes and QRSS

Kevin, AA7YQ, has made innovative use of a parachute. You are right Kevin, this must be a first:

Howdy Bill,
It’s Kevin here in Montana, the ex-Smokejumper. I’ve been meaning to write again. Thanks for the nice comment on SS #100 I got a kick out of it. Anyhow, just thought I’d drop you a note to let you know I finally had a weekend to design and build up a QRSS beacon. I used a Cypress PSoC CY24123A uC to function as the Crystal Oscillator, and keyer. The final is two paralleled BS-170 MOSFETs running in Class-E mode to give me about 560mW out with a 7.5volt Lantern battery as my supply, total system power efficiency is about 63%(RFout over DC in), I’m sure this could be significantly improved, but good enough for now. After several hours of tweaking the capacitor values I finally got the oscillator to fall into the 100Hz window. That was MUCH harder than I had anticipated. With the original version I switched the PA on and off for true QRSS 3 CW, but found this made a significant frequency drift problem. So I added a couple parts and modified the PSoC code a bit, now its running CWFSK, switching about 1.1pF on and off one leg of the XTAL, shifting the frequency about 10Hz and much more stable.

My first tests were with the board sitting on the bench under the desk lamp. This caused all kinds of drift problems. I then put the beacon in a Tupperware container and placed it inside a soft case cooler. I was looking around the shack for a blanket or something to further improve the insulation, when low and behold sitting in a garbage sack… was a condemned FS-14 parachute (equivalent to the SF-10A) that I was planning using for something useful. So I wrapped the chute around the cooler and stuffed it all back in the garbage sack. Surprisingly, temperature stabilization was achieved, beyond my expectations.

The beacon is running good now, nice and stable. I’m fairly certain, that in the history of mankind, no one has ever used a parachute to improve the temperature drift characteristics of a QRSS beacon. Anyhow, I plan on having it fired up quite a bit, so that my antenna is actually put to some good use. It seems I rarely get a chance for one to one contacts anymore. Most of my free time is spent designing and building the radios I never use. Ha. I guess the design and building is the real fun for me.

Anyhow, I’ll talk to you later. 73s Kevin, AA7YQ

PS the Beacon is sending “AA7YQ” followed by a several second pause. It’s showing up on the K6HX grabber between 10.140050 and 10.140060.

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Designer: Douglas Bowman | Dimodifikasi oleh Abdul Munir Original Posting Rounders 3 Column