Alex, if memory serves, the component differences for the lowband
audio/squelch board are documented in the manual. I don't remember if the
station and mobile boards both have different components for lowband, or if
it was just the station. I also don't remember if the SpectraTAC audio
board had different components in the squelch circuit, or if it was on the
Micor mobile or station that did. When I get back to the shop I can dig out
manuals. I forget if the component differences were related solely to
altering the action of the Micor squelch in and of itself, or if they were
also a function of the different AF response (particularly HF noise output)
of the lowband Sensitron receiver.
The Micor squelch circuit is, IMHO, still the best there ever was. However,
the "long" squelch can be a bit too long in some cases when you're using an
audio delay board to mute squelch tails. What ends up happening is that if
you set the delay long enough to fully mute long squelch tails that
sometimes users that are DFQ who un-key quickly will have their last word
chopped off because the short-squelch turn-off is much shorter than the
audio delay duration. Although it defeats the purpose of the bi-level
squelch, what I usually do is defeat the short squelch logic and set the
delay accordingly. I don't have my notes in front of me, but the mod
involves adding a resistor to pull down one of the lines coming off the 7716
to result in the detected noise level always falling in the "long" squelch
voltage range as seen by the comparator.
--- Jeff WN3A
> -----Original Message-----
> From: Repeater-Builder@yahoogroups.com
> [mailto:repeater-buil...@yahoogroups.com] On Behalf Of kq2h
> Sent: Thursday, July 09, 2009 6:13 PM
> To: Repeater-Builder@yahoogroups.com
> Subject: [Repeater-Builder] Micor Bi-Level Squelch Circuit
>
>
>
> I've been impressed with the operation of the Micor bi-level
> squelch circuit based on the M7716 IC. I use Micor
> Spectra-Tac receivers exclusively on 440, 902, 6 Meters and
> 222 MHz (VHF to 222 conversion) with excellent results.
> However, I am perplexed by 10 Meters. The Spectra-Tac squelch
> circuit doesn't work well at all. It squelches up on fading
> signals that aren't all that noisy and drops out for no
> apparant reason. It appears that the squelch is set too high,
> but it isn't. I've tried different audio/squelch modules,
> receiver boards and housings. Even the IMTS modification
> which defeats the short squelch tail doesn't help the
> situation. When a UHF reciever is substituted in place of the
> 10 Meter receiver, the squelch circuit works fine.
>
> An old 25-30 MHz Motrac receiver, with its simple 3
> transistor squelch circuit, works perfectly on 10 Meters.
> There are no problems with drop outs. The receiver squelch
> remains open well into the noise. This leads me to believe
> that the Micor bi-level circuit needs to be optimized for 10 Meters.
>
> Does anyone know of any component value changes in the Micor
> bi-level circuit to optimize operation on 10 Meters?
>
>
>
>
>
> Checked by AVG - www.avg.com
> Version: 8.5.375 / Virus Database: 270.13.12/2233 - Release
> Date: 07/12/09 08:20:00
>
>
>
