You can't beat a really good squelch circuit. Much
as I always seek real alternatives, the dual function
Motorola squelch circuits seem to be some of the best
designs (there is more than one dual function Motorola
squelch circuit). Fast detecting - mute/gate time is
the desired animal.
Spectrum has a semi decent squelch circuit relative to
what it is.
I'm not happy with the slower Hamtronics or Maggiore
squelch circuits although they do work just fine. Slow
squelch circuits are not a major problem when you run
many of the optional audio delay circuits to remove
the crash noise. Even an old ACC RC-850, RC-85 and
an RC-96 controller with an audio delay board would
clean up the more horible squelch circuits (The VHF
Engineering Receivers)
Hence I seek to speed up the squelch gate action of
our new Maggiore 224 MHz repeater. An external squelch
board is probably the most practical answer.
The COS or squelch layout described below is not an
every circuit thing, but it might be typical of many.
Sometimes the high pass filter is a band pass filter
and the detected output is compared to energy at low
and voice frequecies. Response times tend to be much
better (faster).
The common LM-324 and similar op amps can make a nice
squelch - audio mute circuit. You just have to weigh
in your time vs money/resources to pick your poison.
I'm in the process of engineering up a sectional
squelch pc-board for squelch, audio gating - line
driving, ctcss with and/or COR/COS detection. One
simply populates the desired section for their needs.
More as that developes...
The trick is to make it fast using the Micor
Squelch circuit as a relative bench mark.
cheers,
skipp
(ps: A 500mS squelch tail would drive me crazy...)
> Bob Dengler <[EMAIL PROTECTED]> wrote:
> At 6/10/2005 06:56 PM, you wrote:
> >Lets face it, COS or what ever you want to call it is nothing more
> >than a VOX circuit that works on high frequency noise. first the
> >audio goes through a High pass filter of some sort then through an
> >amplifier then to a detector circuit that drives a transistor
> >switch. OH by the way, the switch is used to mute the receiver and
> >viola a squelch circuit is born.
> >NOTHING DIFFICULT ABOUT IT.
>
> ...unless you don't want to hear long 500 millisecond squelch
> crashes. Just ask the engineers that designed the Micor or Mastr
II
> squelch circuits.
>
> Bob NO6B
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