--- In [email protected], DCFluX <[EMAIL PROTECTED]> wrote:
> I am intrested in the conversion procedure for the squelch, I am not
> happy with the audio quality of the midland as well. I was working on
> a new squelch board my self but too busy to sit down and build it then
> write the software.
One of the 2 13-509 repeaters I maintain was modified for "flat audio"
(FM modulator, minimal processing). The other uses the stock phase
modulator. I can't tell the difference between the two.
They both sound good to me, but we had a problem with a 1.5 kHz
rolloff at the discriminator. If you look at the schematic, you'll
see a 1 K resistor on the discriminator output with a 0.1 uF cap to
ground. My guess is that this was a poorly designed LPF to block the
455 kHz. We changed the .1 uF cap (C42) to .01 uF to fix this.
As far as the squelch mod goes, here's what I have in my notes:
C89: replace 4.7 uF with 1 uF or 0.33 uF (I think I used 1 uF; 0.33 uF
made the squelch action a bit too choppy).
C91: replace 4.7 uF with 0.47 uF
Add a 1 megohm resistor between base of TR13 & collector of TR14.
This adds hysterisis which allows the squelch tail to be shorter
without chopping, similar to how the G.E. MVP squelch works.
I have the board layout scanned & will try to post the 1 Mohm resistor
location later.
Bob NO6B
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