HF SQUELCH (WAS Re: [Premium-Rx] Simple clean audio amp)

[Gary Geissinger]

Tim,

I sorta remember the circuit that Dan mentioned and he is right on; it
can get easily fooled.

If you like to homebrew you may want to think about the Motorola "Noise
Gate" type squelch.  Although designed for FM, it may be an improvement
for HF over simple audio/AGC squelch circuits.  The idea is that when no
signal is present, the audio spectral content is different than when a
signal is present.  Motorola filtered, amplified, and detected the (no
signal present) noise.  That signal was then compared to the AGC signal.
When one went up, the other went down and forced a very positive squelch
trip.   

Of course hetrodynes, jammers, etc would still trip it.

I wonder how elegant the ICOM "skip carrier" circuit is in their VHF/UHF
receivers?

73's,

Gary WA0SPM


----------------------------------------------------
This mailbox protected from junk email by MailFrontier Desktop
from MailFrontier, Inc. http://info.mailfrontier.com

-----Original Message-----
From: premium-rx-bounces at ml.skirrow.org
[mailto:premium-rx-bounces at ml.skirrow.org] On Behalf Of k0dan
Sent: Wednesday, March 29, 2006 8:55 AM
To: premium-rx at ml.skirrow.org; Ka9p at aol.com; Tim Shoppa
Subject: HF SQUELCH (WAS Re: [Premium-Rx] Simple clean audio amp)

Hi Tim...

Back in the early 80's the was a circuit (QST??? 73???) for a 2-channel
SSB "smart squelch". Sorry, I don't have the name/author/date anymore,
but I did build one in those days which I used with some success with a
Drake R7 and 51S1, and it was sold when those radios were sold. Perhaps
searching the ARRL site might turn it up.

The problem, however, with any squelch I've ever used on HF, is that
they all get fooled by static crashes, heterodynes, splatter, etc. They
DO work better than riding the RF and audio gain, but they do false, and
if you're listening to (or recording) a bunch of utility channels, it
can get pretty annoying. This is especially so when a broadband
lightning strike opens up ALL your receivers simultaneously, or when a
"sweeper" signal sets them off one by one!

Good luck and 73

Dan
(K0DAN)

>
> Here's a slightly different question:
>
> Say I've got 3 or 4 receivers, each tuned to sideband voice utility HF

> frequencies. I want to be able to monitor these frequencies but don't 
> want to listen to the audio unless there's a signal present. This 
> implies some kind of squelching ability. Radios are not identical but 
> generally have AGC level out or IF out ability (actual levels vary 
> from radio to radio.) Is there a "common" solution to this problem? I 
> look at say old WJ price lists and see squelch as an extra-cost 
> option, but I'm not about to pay those kinds of prices :-).
>
> With some radios I can turn AGC on and turn the RF gain down to the 
> point where background static isn't objectionable, and then when a 
> signal comes in the AGC takes over. But... AGC on my WJ-8716's doesn't

> work this way! (Is it supposed to? If I turn on AGC I have no manual 
> RF gain control, and if I turn on RF gain control I have no AGC. This 
> is different than my other receivers.)
>
> Tim.



_______________________________________________

Premium-Rx Mailing List
To Post: premium-rx at ml.skirrow.org
For Info: http://ml.islandnet.com/mailman/listinfo/premium-rx
Visit the Website: http://kahuna.sdsu.edu/~mechtron/PremRxPage/