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CWB
Posted: June 02, 2010 11:23 am
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yessir ...
and why you can actually "hear" any intelligence is due to "slope detection" .
/me remembers a cheapo vhf receiver that used this ... sounded like crap .


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tekwiz
Posted: June 02, 2010 04:54 pm
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QUOTE (Village Idiot @ June 01, 2010 04:04 pm)
A stong FM signal can find many places in a circuit to resonate and get detected. I've picked up local FM stations on a few different AM band crystal sets.

For this challenge I've decided to build an FM crystal set with some audio amplification. In the test circuit so far I've managed get get a few local stations, but guess what? I'm getting a local AM station coming in too. However, a 10µH choke in parallel with the detector diode fixed that problem.

You might be able to get rid of the FM station doing a similar thing. Try shunting the detector diode with a 5 or 10 pF capacitor.

If you don't have a cap that small, a couple of pieces of hookup wire tightly twisted together & about an inch long will make a good substitute. wink.gif


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Roccivic
Posted: June 02, 2010 05:46 pm
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QUOTE (tekwiz @ June 02, 2010 03:54 pm)
QUOTE (Village Idiot @ June 01, 2010 04:04 pm)
A stong FM signal can find many places in a circuit to resonate and get detected. I've picked up local FM stations on a few different AM band crystal sets.

For this challenge I've decided to build an FM crystal set with some audio amplification. In the test circuit so far I've managed get get a few local stations, but guess what? I'm getting a local AM station coming in too. However, a 10µH choke in parallel with the detector diode fixed that problem.

You might be able to get rid of the FM station doing a similar thing. Try shunting the detector diode with a 5 or 10 pF capacitor.

If you don't have a cap that small, a couple of pieces of hookup wire tightly twisted together & about an inch long will make a good substitute. wink.gif

I bought a large box of assorted caps a few years ago, after sorting I discovered 1pF ceramics. They almost pointless though...
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Jawno
Posted: February 20, 2012 04:52 pm
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Did everyone just give up on the challenges? I used to enjoy reading the solutions and felt they improved my electronics knowledge. Did you run out of puzzles or did it just get to be too much to deal with? No biggie either way but I used to enjoy them when I first joined the forum here. Any chance of reviving them?
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