[aprssig] Burst after voice (was pointless text)

Stephen H. Smith wa8lmf2 at aol.com
Thu Jun 1 11:10:48 CDT 2006

wes at kd4rdb.com wrote:
> I
> I _think_ I've also discovered a bug in the TT3's implementation of 
> the burst after voice too... my TT3 is hooked in series with the mic's 
> PTT and should assert PTT after my mic has pulled PTT low.  It should 
> continue to hold PTT low until I unkey, send data, then release PTT.  
> But instead it does not clamp PTT.  It seems to wait for me to unkey, 
> then assert PTT and send data.  This causes the radio to go thru a 
> full TX->RX->TX cycle and prevents me from running a TXDelay of less 
> than 150mS.  I think we should be able to run a TXD of 50mS in this 
> mode though.  On a nearby HT, I can hear a little static crash between 
> when I unkey and the data is squirted and on the radio I'm talking on, 
> I can see the PTT indicator do a little 'double dip'. I'm not sure if 
> this is a problem with _my_ TT3 or all of them.  I asked about this on 
> the TT yahoo group and got no answer and also have email Byon and he 
> said he's looking into it.  Does anyone here have any experience with 
> this?

I've observed the same thing using the TinyTrak in my APRN system where 
the APRS burst follows an SSTV transmission.  The radio definitely 
unkeys and then rekeys between the video and the packet burst.  

I'm considering adding a hardware pulse stretcher kludge downstream from 
the TT to bridge the unkey-rekey hiccup.  


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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