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[aprssig] Mic-E and HTs

Stephen H. Smith wa8lmf2 at aol.com
Tue Dec 13 18:37:43 UTC 2005

bruninga at usna.edu wrote:

>>>>"Scott Miller" <scott at opentrac.org> 12/12/05 4:22 PM >>>
>>Right, I follow all of that, but it doesn't address 
>>the issue of most handhelds ... which key PTT 
>>through the audio line. 
>Works the same way, but in addition to the diode
>bypass from the PTT input to the PIC to the PTT
>output from the pic, you just add a capacitor too.
>Ill draw it...
>See http://www.ew.usna.edu/~bruninga/mic-ePTT.GIF
>de WB4APR, Bob
>----- Original Message ----- 
>From: "Robert Bruninga" <bruninga at usna.edu>
>To: <aprs at kd4rdb.com>; <aprssig at lists.tapr.org>; <scott at opentrac.org>
>Sent: Monday, December 12, 2005 1:15 PM
>Subject: RE: [aprssig] Mic-E and HTs
>Mic-E PTT mode of operation:
>>First it has to sense what the status of PTT is so that it
>>can know when you release PTT so it can inject the packet.
>In PTT mode of operation, the Mic-E processor has to
>have a PTT input and a PTT output.  The microphone
>PTT switch has to be connected to the Mic-E PTT input
>and then the Mic-E processor has to then detect this
>and then output its own PTT onward to the rig.
>This is so that the Mic-E processor can sense the
>release of PTT by the operator, but *still keep PTT
>asserted* on its output until after the packet
>burst.   There cannot be any drop of PTT to the
>rig between release of the operator and end of
>the packet, or all the advantage of the PTT mode
>is lost because the TX will begin to shut down,
>the PLL will begin to switch to receive, and the
>receiver squelch of the other guy will begin to act.
>And this would then require an additional TXD
>delay to allow all that to happen.  Thus, turning
>the 150 ms Mic-E PTT mode burst into a full
>sized 500 mS packet.
>So, the Mic-E input PTT and PTT output are separate.
>Now, it is a good idea to connect a diode from the
>PTT input circuit to the PTT output circiut so that
>the microphone and radio will work normally even if
>the Mic-E circuit is turned off or the Mic-E processor
>fails.  COnnect this diiode with its cathode on the
>Mic-E input and its anode on the Mic-E output.
>Hope that helps
>Bob, Wb4APR

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.    
This setup may allow the packet burst to go out when you key and then 
unkey, but you'll never be able to talk!!

Stephen H. Smith    wa8lmf (at) aol.com
EchoLink Node:      14400    [Think bottom of the 2M band]
Home Page:          http://wa8lmf.com

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