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[aprssig] Burst after voice (was pointless text)

Wes Johnston wes at kd4rdb.com
Thu Jun 1 14:21:03 UTC 2006


I love the idea of using PTT mode on the kenwood... a mic-e burst at the end 
of voice transmission, however there is a problem with the kenwood 
implementation.... and the TinyTrak inplementation too...

For some reason, every 5th or 6th odd time I send a position using the PTT 
burst after voice method on the kenwood d700, the radio actually unkeys for 
anywhere from a brief instant to 2 seconds then re-keys the radio and 
transmits my position.  It's almost like the TNC in the radio was distracted 
at the moment I unkeyed and then tried to catch up.  I suspect it's in the 
process of collecting a GPS sentence at the moment I unkey.  It's 
aggrivating and frequent enough that I gave up trying to use the mode.  It 
sometimes takes up to 2 seconds to finally decide to keyup and send a 
position... enough time for the other party in my QSO to start talking and I 
miss part of what he's saying.... which is the whole reason for using the 
PTT burst method in the first place.  Instead I attached a Tiny track 3 to 
my mic cable and used that set to the same callsign as the kenwood to send 
positions.  The kenwood can still send messages though, and it still 
receives data and plots to my GPS.

Also, just to split hairs, the d700 has a fixed txd of 500ms, which is 
annoying for mic-e use... I sure wish it was able to be changed like the 
d7 - or that it had the smarts enough to realize that it only needs long 
txdelay when the radio isn't already on-air.  So with a d700, the mic-e 
burst is actually 500mS of txd + 100mS of data.  Still it's an interesting 
mode.

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?

Wes


----- Original Message ----- 
From: "Robert Bruninga" <bruninga at usna.edu>
This use of PTT mode (.1 second burst on the end of
a voice transmission) is exteremely efficient and makes
operations at an event very practical.  In fact, it lets
all the D7 and D700 users use TWO simultaneous voice
frequencies on their radios.







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