[App_rpt] Radio Interface Question

Wed Mar 8 06:31:51 UTC 2006

Its a really easy thing. The two speaker outputs (which are a bridged audio 
out) stay at Gnd DC
potential until there is something for the receiver to receive. So, if you 
do something like this:

Keep Volume control about 9 o'clock on radio.

   ____________________________ Rx Audio
   |
   |
   |   47  .25W
---|--/\/\/\/\------|
Spkr Lo            |
       47  .25W  |_________________ COR
------/\/\/\/\------|
Spkr Hi         __|__
                   _____ .01uf
                       |
HT600 side       |
                       |
                    Gnd

The transmit audio just needs some sorta voltage divider (like maybe 5:1).

>From: Steve Rodgers <hwstar at rodgers.sdcoxmail.com>
>Reply-To: Asterisk Repeater Controler <app_rpt at lists.illiana.net>
>To: Asterisk Repeater Controler <app_rpt at lists.illiana.net>
>Subject: Re: [App_rpt] Radio Interface Question
>Date: Tue, 7 Mar 2006 21:10:29 -0800
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>James,
>
>See below--
>
>
>On Tuesday 07 March 2006 15:28, James Harfield wrote:
>
> > Measuring the levels of the speaker audio, regardless of volume level
> > on the radio, the voltage does not break 1.5v.  Looking at the
> > documentation for the card I felt that this was appropriate.
>
>The potential problem here is that someone can mess with the receiver 
>volume
>control and mess up the audio levels.
>
> >
> > I'm using regular Ground as of now.  Grounding PTT with "Ground" and
> > not "RF Ground" keys the radio as it should.  So I'll just move my
> > ground pin to there and leave PTT where it is.
>
>Sound like a good plan.
>
> >
> > What I'm doing now is making a small circuit to work as COR.  I can't
> > seem to find a working version of the COR in the radio pin out, so I've
> > taken a MOSFET and 5v battery to switch the level from 5v to ground when
> > a signal is present and stay at 5v when no signal is present.  Unless
> > I'm blindly missing something to pull off the radio that will work the
> > same way.  Something like:
> >
> >                       +5v
> >
> >                          10k
> >                        _ |--------------to PCI card
> >
> > >from radio-- |_
> >
> >                         gnd
>
>May I suggest you get the schematic to the radio, and look for the 
>transistor
>or electronic switch which is used to mute the audio? If you can find some
>point in the squelch circuit which swings from 5 volts or higher to ground,
>use this as your COR. The COR input as a 1 megohm input impedance. You 
>should
>be able to find a point in the radio which will provide the signal for you.
>
> >
> > ASCII art may be butchered in the post though.  The level from the
> > radio should be enough to activate the FET and pull that output to
> > ground, while allowing the 5v to pass to the card when there is no
> > signal.
> >
> > Just for reference so you know where I'm coming from, I found a couple
> > of Motorola HT600s on eBay with charger for pretty cheap and am playing
> > with those since they seemed to have easy access to signals with the 13
> > pins on top.  I thought this would be good to learn with while not
> > investing tons of money in expensive radios to break.  Thanks for the
> > help while I struggle through this process.
>
>HT 600's should interface nicely. Take a look in the service manual to
>understand what I'm talking about. The way the speaker circuit works, also
>doubles nicely for COR. The audio output stage is powered down when there 
>is
>no signal.
>
>
>
>
>
> >
> > -JRH
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