Hi all,
I'm looking for a _simple_ automatic noise limiter (or noise gate) for non-hifi use like AM radio. I remember ANL in old CB transceivers using very few components but can't find any schematics. Googling just returns equipment stuff, no schematic :(
Tom
Find a point in the audio path where you expect the signal to be about
1 - 1.2 Vpp, and put antiparallel signal diodes to ground there, like 1N914s or 1N4148s. You shouldn't have to add any resistors, because existing impedances should take care of that. That just simply limits the P-P voltage excursion; it doesn't make the noise go away (it's not a noise _blanker_), but it does _limit_ it to at least a reasonable signal level. You could even put it in a gain-controlled circuit and play with limiting of ordinary audio - voice, anyway, can take a surprising amount of limiting and still be intelligible. Some people call this "clipping", but I think clipping has much sharper "corners", where limiting softens them a little. :-) (that's the corners on a 'scope display, has nothing to do with bandpass. :-) )Hope This Helps! Rich
What I need, to be more precise, is to mute very small signals like a background hiss and, if any greater or normal signal kicks in, the "gate" opens and everything goes through.
Tom
"T. Atkin" schreef in bericht news:0%d2g.15811$U% snipped-for-privacy@weber.videotron.net...
Maybe when you google for squelch?
petrus bitbyter
or noise gate
Finally I had more success with "noise gate". I found out that "squelch" and "ANL" are not good choices because, in radio circuits, they are activated by the carrier level; when a carrier is present, the extracted AGC signal which is a DC signal is used to unbiase a diode, that diode normally shunts the audio signal path. That's why these circuits are so simple. Won't work with my actual design, no carrier here, but I know now how they shunt the audio, I'll have to convert the audio into dc to control the gate.
Regards! Tom
Oh! Well! That's different!
Never mind. ;-)
Cheers! Rich
The simplest discrete component squelch circuit takes the form: View in a fixed-width font such as Courier.
. . . . . . 1N914 1N914 . IN>--+---|>|---+---|OUT . | | | . [R] | [R] . | [R1] | . --- | --- . | . | . Vbias . . .
This goes in the small signal audio path. The through path is blocked by running Vbias up to the most positive circuit voltage, and the path is connected by pulling Vbias less than the signal DC common to set up DC bias currents of say x10 the largest audio small signal current. The bias can be controlled by any number of amplitude detector circuits. This circuit is not appropriate for high fidelity audio. You would want to use an analog switch IC in that case.
In that case, I may well use a 4066 or, better yet, a 4053. I should be easy to drive its control gate. I think I will go this way.
Thanks! Tom
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