Motorola copied their own Micor squelch action in the MSR2000 audio
card without using the Micor chip. Looking at the manual for it makes
a nice bit of context for the micor circuit.
I think Kevin hit the nail on the head with the really, REALLY good
squelch action you can set right at the ragged edge without false
triggers. Since I use audio delay boards in my repeaters, the micor's
closure action is not as nice as the really really nice "hairy edge".
I've actually noticed that the MSR2000 works just as well for this...
and dare I say... personal preference, prefer it to the Micor.
I've played with several noise squelch designs. Zetron even included a
"bi-level" squelch in one of their controllers... 45? 48? I don't
remember now. In any event, if it's the no noise-burst you're looking
for then simply adding another comparator that triggers about 10db
above the first (assuming you want it Motorola style), and when it
triggers it disables the time delay circuit of the first (read:
discharges the timing capacitor). When the signal is removed, the
timing capacitor has no time to charge between the time the "strong
signal" comparator shuts off and the "weak signal" one does, hence no
noise burst.
If you have a spare couple of hours, playing with building squelches
if really pretty fun and easier than you might think. Grab a
breadboard, your favorite active filter calculator, a couple of op
amps and a couple of comparators and have fun!
73 DE N0MJS
On Dec 22, 2008, at 7:05 PM, Kevin Custer wrote:
Jordan, et al,
The RLC-MOT circuit uses the famous Motorola MICOR squelch chip, so it
works identically to what is found in the MICOR. Motorola decided some
time ago to end the production of the chip, and I suspect the recent
jump in cost is a result of this. As Scott has mentioned, I did a test
of some of the commercially available add-on squelch boards that were
advertised about two years ago. This included the NHRC-Squelch, the
CAT
SQ-1000, and the Link-Comm RLC-MOT.
The following is a personal opinion - no more, no less. The best one I
found is the RLC-MOT, but then again, I find no fault with the
action of
the MICOR squelch. In my opinion, there is no better. The other two
work fairly well, and I don't remember if one was any better than the
other. The biggest fault I found with the latter two units is (in my
opinion) they don't have enough sections of high-pass filtering, and
low
frequency noise is considered in the evaluation. This tends to make
the
user set the squelch tighter than he/she should have to - - to keep
the
unit from falsing. This may not be a big deal for some, but I like to
have a squelch I can set on the hairy edge without falsing, like the
MICOR squelch. Both the NHRC and the CAT have near instant turn off
when the carrier is near full quieting and then removed. They both
have
'variable' hysteresis - as the signal is reduced, they produce a
longer
noise burst after removal of the carrier. In the NHRC, there are four
progressive steps with differing time - depending on how it's
configured. The manual for the CAT unit doesn't offer how the time
delay is handled. They both use a processor to evaluate the noise and
set the amount of hysteresis. The MICOR has only two different
hysteresis levels.
As the availability of the MICOR squelch gets increasing higher in
cost,
or becomes no longer available, these other units may be the only
choice
for those who want to replace the carrier squelch circuitry. That
being
said, Scott and I have done a great deal of research and believe we
can
reproduce the action of the MICOR squelch with circuitry that doesn't
include a micro-processor.
Kevin Custer
> Jordan,
>
> The RLC-MOT works very well since it is an exact copy of the
squelch circuit
> found in the Micor. The only problem is it is now VERY expensive.
>
> Kevin had done some extensive testing on the dual squelch modues
some time
> ago. Maybe he can chime in here... Kev??
>
>
>
>> Anybody have any NHRC-squelch boards in service? I am looking at
>> getting either one of those or a RLC-MOT board from link
>> Communications. Is one better then the other? Do they do the same
>> thing? Anybody try to clone an NHRC board? (they look easy) I am
>> wanting to install something on a Mitrek for that nice Micor type
>> squelch. Actually, I just want to get rid of that Chkccccccccccc!
--
Cort Buffington
H: +1-785-838-3034
M: +1-785-865-7206
