[Premium-Rx] Re: HF SQUELCH

[Larry Gadallah]

On 3/29/06, premium-rx-request at ml.skirrow.org <
premium-rx-request at ml.skirrow.org> wrote:

> ------------------------------
>
> Message: 5
> Date: Wed, 29 Mar 2006 09:55:19 -0600
> From: "k0dan" <k0dan at comcast.net>
> Subject: HF SQUELCH (WAS Re: [Premium-Rx] Simple clean audio amp)
> To: <premium-rx at ml.skirrow.org>, <Ka9p at aol.com>,        "Tim Shoppa"
>         <shoppa at trailing-edge.com>
> Message-ID: <00b401c6534b$baef10c0$6601a8c0 at k0dan>
> Content-Type: text/plain;       charset="iso-8859-1"
>
> 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)
>

I spent a fair bit of time looking for options for such a "smart" squelch or
to be more accurate, a syllabic rate squelch.  The idea is that syllables in
speech contain energy in certain ranges of the audio spectrum, and if you
measure the energy in these ranges, there is a characteristic rate at which
the energy appears and disappears, hence the name "syllabic rate".

There were indeed a couple of circuits published in 73 and QST in the 70's
and 80's, as well as this one (http://www.ah6le.net/hf_squelch.html) from
someone in the Echolink/IRLP domain, and they all probably work fine. If you
search the patent databases, you will find literally dozens of patents
related to this concept. What I found in the way of off-the-shelf solutions
was limited to an expensive unit intended for marine use from an outfit
called Naval (http://www.naval.com/vos.htm), and the Ten-Tec kit mentioned
earlier.

What I really wanted to know was how to implement this in DSP, so that it
could done using a PC and a soundcard. I found lots of theory, but not much
practical.

Cheers,
--
Larry Gadallah, VE6VQ/W7
lgadallah AT gmail DOT com
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