Concept:
Enable PL tone on transmit all the time, and keep the PL encoder from keying the exciter.

Description:
The unmodified PL encoder will give reverse burst when exciter is unkeyed. This may be undesirable in amateur communications since most amateur radio equipment does not support reverse burst. Also in the process of providing the reverse burst the PL encoder keeps the exciter keyed, and in some models will not let the exciter unkey.

Benefit:
Enables PL on transmit at all times, removes reverse burst capability, and does not allow the PL encoder the ability to key the exciter.

Modification:
Cut R726 at junction of CR702, then ground the clipped end of the resistor. This sets the PL tone gate to "ON" all the time. Desolder or cut out Q707 entirely, this disables the ability of the PL encoder to key the exciter.

See this 1.5 MB PDF file for documentation of the TLN4293B PL Encoder board for parts identification and location.

See this 1.3 MB PDF file for documentation of the TLN5731A PL Encoder board for parts identification and location.

NOTE:  Ensure that the jumper between interconnect pins 8 and 10 on the exciter exists, otherwise the transmitter will not key.

Allan Perrins WB6PHE adds this bit of information on a Station Configuration:

On the exciter board, cut the trace leading from pin 5. On some MICOR Stations, the decoder tone may be routed to this pin and interfere with the operation of the encoder.

I have fought this problem for the last two days. The repeater worked fine until I put the decoder in place. Then, no transmit tone anymore. Took the tone board out, ran it on the bench, works fine. Put it in the chassis, no tone. On and on it went, as I said, two days worth. Cutting the trace on the exciter board was the easiest way to eliminate the problem.

Allan, WB6PHE
 
 
 
 

HTML Copyright©  1-25-98 Kevin Custer W3KKC
Added WB6PHE information 10-07-2003  W3KKC
Added TLN5731A documentation 10-19-2020  WA1MIK