Something Weirdly This Way Comes - Beacon Trouble Edition
I had some temperature beacon trouble at the remote location. When I tried listening Sunday morning all I heard was a carrier - it turned out to be my beacon was key-down. The beacon has been running 24 / 7 / 365 for years without a problem. Here's a picture:
The old Knight CB talkie is OK, the wall wart seems OK. But the beacon in the tin is NG. It is a PIC based beacon which reads and transmits the temperature in degrees Fahrenheit every 10 seconds or so. I also used an op amp to scale the LM-34 sensor voltage and an external voltage reference for the PIC A/D. There is also a piezo at the lower right which clicks in time to the Morse.
Diagnosis: Is the keying transistor bad ? It is a 2n7000 MOSFET. I tried replacing it. The beacon worked BRIEFLY but then went key down again.
Then it dawned on me: what about the jack ? There is a 3.5 mm stereo jack to the Knight CB which brings ground, +9V and the keying drain output of the MOSFET. I noticed that the plug from the Knight CB was REALLY hard to remove. So I tried rotating the plug and voila ! The beacon started to work. Just for grins I put the original 2n7000 transistor back and it still works. It must be metal fatigue or maybe it was just the cheap jack.
So as might be expected, the problem was a mechanical thing, the connector. I'll have to replace it with something better. I think I have some beefy Switchcraft 3.5 mm panel mount jacks around here which should be better.
Best Regards,
Chuck, WB9KZY
http://wb9kzy.com/ham.htm
The old Knight CB talkie is OK, the wall wart seems OK. But the beacon in the tin is NG. It is a PIC based beacon which reads and transmits the temperature in degrees Fahrenheit every 10 seconds or so. I also used an op amp to scale the LM-34 sensor voltage and an external voltage reference for the PIC A/D. There is also a piezo at the lower right which clicks in time to the Morse.
Diagnosis: Is the keying transistor bad ? It is a 2n7000 MOSFET. I tried replacing it. The beacon worked BRIEFLY but then went key down again.
Then it dawned on me: what about the jack ? There is a 3.5 mm stereo jack to the Knight CB which brings ground, +9V and the keying drain output of the MOSFET. I noticed that the plug from the Knight CB was REALLY hard to remove. So I tried rotating the plug and voila ! The beacon started to work. Just for grins I put the original 2n7000 transistor back and it still works. It must be metal fatigue or maybe it was just the cheap jack.
So as might be expected, the problem was a mechanical thing, the connector. I'll have to replace it with something better. I think I have some beefy Switchcraft 3.5 mm panel mount jacks around here which should be better.
Best Regards,
Chuck, WB9KZY
http://wb9kzy.com/ham.htm
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