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[aprssig] Mic-E and HTs

Robert Bruninga bruninga at usna.edu
Wed Dec 14 00:41:00 UTC 2005


I think that the 2.2k is negotiable, depending on the
rig.  THe larger the resistor, the less load ing on the
mic.  I hope someone else has looked at all the rigs
and decided what the typical PTT pulldown impedance
is supposed to be?  Bob

>>> scott at opentrac.org 12/13/05 4:10 PM >>>
Ok, now you've got basically what I came up with.  Only I wasn't able to get 
PTT detection directly from the I/O pin (this was with a Motorola GP68 
handheld, don't remember the troubleshooting sequence exactly) so I added a 
transistor there.

The only problem I've encountered with this setup is that the audio is lower 
than I'd like.  Larger values for the capacitor help, but I think I'm still 
going to have to add an op amp or transistor there.

But my question remains - has this always been the accepted way of doing it? 
Why isn't there any documentation out there about it?


----- Original Message ----- 
From: "Robert Bruninga" <bruninga at usna.edu>
To: <wa8lmf2 at aol.com>; <aprssig at lists.tapr.org>
Sent: Tuesday, December 13, 2005 12:59 PM
Subject: Re: [aprssig] Mic-E and HTs

>>> wa8lmf2 at aol.com 12/13/05 1:37 PM >>>
>bruninga at usna.edu wrote:
>>Ill draw it...
>I don't see how the second half of your diagram
>(the part labled "Combined PTT" could possibly work.
> You show one side of the mic element grounded all
>the time with PTT button then grounding the other
>side, thereby shorting out the audio.

Argh, your right.  I was too quick to draw that.
I fixed it now with the typical 2.2k resistor...



Stephen H. Smith    wa8lmf (at) aol.com
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