[aprssig] TM-D700A question

Stephen H. Smith wa8lmf2 at aol.com
Tue Sep 6 04:20:48 CDT 2005

dave at emv.co.uk wrote:

>In any case, it only works AFIK for users with the D700 rig...  D7's,
>trackers, radio's and TNC's etc, wont open a new RX audio path.
>Dave B.

This issue generates a flame war on this SIDE of the Atlantic also every 
time Bob brings it up!

 From a technical standpoint, however, radios other than D700s CAN do it.  

Connect the TNC directly to the discriminator of the FM rig (such as the 
"9600 baud" pin of the miniDIN-6 "data" connector on a radio so 
equipped) rather than the speaker jack.  You can then enable PL to mute 
the speaker until someone transmits a PL'ed voice signal,  meanwhile the 
TNC will always receive data.  

Radios with TX-only trackers can do the same thing.  Setting PL-muted 
receive won't affect their ability to transmit.  The only effect on 
simple trackers  like TinyTracks is that PL muting will prevent their 
audio-sensing DCD channel-busy function from working to inhibit transmit 
on a busy channel .  You can work around this by using the "SQUELCH" or 
"BUSY"  line on the miniDIN-6 packet jack, which provides an indication 
of activity whether or not you can hear it in the speaker.   Or grab the 
DC line that lights up the "BUSY" light on the front panel. 

Note that the intent of "Voice Alert" is for mobiles only (never fixed 
stations, especially digipeaters)  to transmit the PL'ed signals.  When 
a  PL-transmitting  APRS mobile is within direct (not digipeated) range 
of your PL-muted mobile (i.e. within just a few miles) your speaker will 
unmute and let you hear the packet brrapps on 144.390 .   Even if you 
DON'T make a voice call on the APRS channel, it does alert you to the 
presence of another mobile within 2 or 3 miles.  

Another question: 144.800 may be safe from this in any case.  Is the 
Euro version of the D700, etc even capable of PL encode? I seem to 
recall it only does 1750 tone bursts on keyup. 

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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