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If you use this,: http://space.tin.it/scienza/fladelle/Page16.htm and put an SPDT relay in place of the leds, you should be able to just use the normaly closed contact of the relay to switch your... thing, I don't know what you are trying to build, but will that work?
I want to make a Dead Air detector for a radio station.Its work like this.
I can feed my radio out put to a circuit (audio silence detector),that cirucit gives me some signal when audio stopped by some reason.From that trigger we can program a ADC to run some application in one computer whihc will play out again some temp music content back to transmitter.
This works fine if your transmitter far away from your studio, and ur studio transmitter Link is gone down.
Hi everyone, im looking for a tested squelch circuit for an FM radio, that i modified for the 2m band.
The radio is built around a cheap KIA6040 IC.
I dont have much experience with radios, so it would be better for a squelch, that i could put just right before the speaker.
Normally I'd say something about how it's not a good idea to resurrect a thread that's over three years old, but at least you picked one that was relevant.
The most straightforward way I see to do it would be to use a peak detector, followed by a low-pass filter, followed by a comparator with some hysteresis. If the input signal is too low of an amplitude to use effectively with a basic diode peak detector, you can easily throw an op-amp amplifier before the peak detector. The output of the comparator will then just be a digital indicator of whether there's a certain level of signal on the input, and you could use it to drive a relay or whatever you want to switch. You can adjust the switching threshold by adjusting the voltage threshold of the comparator, and/or adjusting the gain of the amplifier if you use one.
I converted a low cost Radio Shack weather radio to run at close to 150 mHz to listen to police/emergency calls - as described in a magazine article about 20 yrs ago. I distinctly recall that the squelch circuit was pretty simple - a capacitor and a muting circuit. In this case the audio was generally higher in frequency than voices - the capacitor conducted better at the higher audio frequencies. I was quite pleased with the way it worked - not quite as reliable as my modern 2 meter rigs but sufficient. You might develop your own - capacitor and diode to provide varying DC based on audio - to a muting circuit. Yes, this was affected by volume control setting.
Yes, basicly i need a high-pass filter (RC) with the cutting frequency of about 5kHz. Than i would have to ampify the noise (with a freq. higher than 5kHz), detect it with a diode, and use to switch off the speaker. (or the audio amp)
...but, if someone has a working one (or a link), please let me know. Thanks.