[App_rpt] Radio Interface Question

[James Harfield]

Steve Rodgers wrote:

"A couple of things to note here:

Tying speaker audio to RXA is not the preferred method. RXA should be
tied to 
the receiver's discriminator output, or to a point where the audio
levels are 
less than a couple of volts peak. 

Pin 8 should be tied to DC ground. If that is the same as RF ground,
that's 
fine.

Microphone inputs tend to be very sensitive. You might need to add some

attenuation resistors to the microphone input to knock the audio level
from 
the card down so that you can easily adjust the level. If there is a
line 
level input to your transmitter you'd be better off using that."

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.

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.

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

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.

-JRH