[EMAIL PROTECTED] wrote:
At 1/26/2007 16:09, you wrote:
The only thing I can say is try one for yourself. If you don't want to
spend the $50 or so on the Link-Comm unit (cheap in my opinion), you can
adapt a Micor audio/squelch board into a Mastr II, or get a chip off of a
board and build one of these circuits yourself - maybe for a little less:
<http://www.repeater-builder.com/micor/pix/newbilevel.gif>
Hope this helps...
Kevin Custer
Hmmm, that's an awfully big capacitor hanging off of pin 10. I assume that
"COS out" is used to drive some visual indicator, as the 2.2 µF cap. will
prevent really fast short squelch (< 3 millisecond) closing action.
That capacitor size is what is in some Mobiles and all Station A&S boards.
In a Micor EMS mobile repeater, its value is 3.3 uF.
FWIW, I never use pin 10 at all;
I try to use that pin when I can, and prefer it over the open emitter
shunt switches. The pin is not used elsewhere in the Station, it's
only connected to the 2.2 uF cap to ground. In most Mobiles, the value
of the pin 10 cap is .47 uF. and the signal there is called RUI
(receiver unsquelched indicator).
I use this circuit to buffer the output of pin 10. It was copied
directly from the Railroad Micor:
http://www.repeater-builder.com/pix/cosswitch.gif
It was in working with the Railroad Micor that I found that using pin 10
of the chip (pin 8 of the A&S board) and the associated transistor
buffer to be my choice of COS generation when using the Micor Squelch
Chip. In the Railroad Micor, the value of the pin 10 cap is 2.2 uF. It
might be that 2.2 uF is too big to achieve 3 millisecond or less
closure, but I never thought using this value made it too slow? Most of
our conversions are Mobiles, where the default value is .47 uF. It
might be that this output is fairly robust, and the actual value is not
critical... I don't know, I never measured the differences when using
different size capacitors here.
the circuit I've been using is at
http://www.tasma.org/micorsq.png.
I see some potentially major problems with the TASMA circuit, as it is
not a replica of the OEM Motorola circuitry; like the one I provided.
I see a potential for problems with the values of the capacitors
associated with the input pre-emphasis, they are C3, and C4 in my
diagram. The series cap after the squelch pot is 15 times smaller than
OEM, and the cap across the pre-emphasis resistor is twice the original
value. Then is the value between pins 1, and 2; it's less than half the
OEM size and with a 100 pF hanging on the output, that's a big deal.
Then is the cap going to pin 4, likely not a big deal, but we've already
made several caps in this chain smaller than OEM. Then is the obviously
too small power supply decoupling cap on pin 9 (.01 uF) after the 15 ohm
series resistor. The squelch chip draws some current, and a .01 is just
too small. These values are *very* inconsistent with the OEM Micor
circuitry. Maybe they don't make that much difference in real world
use, but I'll bet my money on the original Micor circuitry.
YMMV...
Kevin
