WTD Simple Audio Squelch

[Carl WA1KPD]

Hey all,

I have a Lafayette 6 mtr AM rig w/o squelch. After many hours the HISSSSSSSSSSSSSSSSSSSSSSSSSSS is getting to me.

Is there a simple outboard squelch I can addd?  Solid state is fine (head hanging in shame)

I just want to end this torture quickly

73 and tnx

Carl /KPD

[Ed-VA3ES]

Hey all,

I have a Lafayette 6 mtr AM rig w/o squelch. After many hours the HISSSSSSSSSSSSSSSSSSSSSSSSSSS is getting to me.

Is there a simple outboard squelch I can addd?  Solid state is fine (head hanging in shame)

I just want to end this torture quickly

73 and tnx Carl /KPD

I've got the same rig, Carl and the same complaint. I'm currently researching carrier and AGC  squelch circuits from many sources.    When I've got my solution, I will post it here (AMFONE.net).

[Carl WA1KPD]

Tnx Ed

73

Carl /KPD

[Ed-VA3ES]

I have a  whole slew of rigs - Hallicrafters CB-3A, various CB radios, various amateur rigs, including a Polycomm 6,  plus other AM radios with squelch (including some aircraft radios).  Some are solid state. I will compare those circuits and choose the best and easiest to implement.

[WU2D]

The most primitive squelch I have ever heard of is the one in the R390. It is simply one triode section of a 12AU7 with the grid hanging off the detector driving a relay! I think it has three resistors and a cap. I will try to dig up the schematic.

Mike WU2D

[WU2D]

Well Carl,

Nobody coming forth so I collected a few squelch ideas for you. The R390 Squelch is pretty simple and is nothing more than an AGC based control gate using the 12AU7 to drive a relay. This type of squelch can come in several flavors but they all do about the same thing. The control gate (Tube Transistor Fet or IC) changes state when the AGC voltage goes down and this cuts off another device like a transistor or tube amplifier making it go into Class C and stop working. The control device can also directly control a gate like an analog switch, a shunt or series diode switch or device or in the case of the R390 a relay! The RSSI or S-Meter circuit can also sometimes be made to function as a squelch input.

A more elegant squelch circuit is the true noise squelch or TNS. This circuit takes some of the audio above 4 kHz by using a bandpass or high pass filter scheme and amplifies it and rectifies it to produce a voltage. When a strong signal comes on, the noise is quieted, and the in turn voltage goes down. If you can sense this (in a comparator for instance), you can use it to similarly trip a gate or bias an amplifier off. Voice audio below 4 kHz does not effect the circuit. Hysteresis is sometimes required for excellent performance.

There are many variations, both simple and complex based on these themes.

73's and Good Luck!

Mike WU2D