From my helpful hints page
https://www.navy-radio.com/tty/ugc136.htm

DB25M connector - Pin 1 for RXD, Pin 2 for TXD, Pin 24 for signal ground - See page 8-5

So data from your TU is applied to pin 1 and ground. Data to your TU comes from pin 2 and ground. 
Or for testing, just connect pin 1 to pin 2. 

Normal Mark is -5v, Space is +5v
There is an invert switch that will reverse this. 
The invert switch is only sampled during power on. 

Ignore pins 13, 14, 17, 18 unless you are installing aboard a warship and connecting to some unknown equipment……..

Nick England K4NYW
Chapel Hill NC
www.navy-radio.com


On Sun, Feb 1, 2026 at 8:14 PM Fred Weksberg <VE3PIE@outlook.com> wrote:

I am trying to get this connected – and hit a roadblock

The receive +/- 5 volts goes into the back panel J2 connector. I am looking at the schematics but it is not clear to me which pin does what.

The manual says:

 

                 J2 connector pin #

RxD1                   1                           for the Rx:  which is +5v, -5v, and GND ?

RxD2                   13

RxD3                   17

             

TxD1                    2                          for the Tx:  which is +5v, -5v, and GND ? 

TxD2                    14

TxD3                    18

 

Can anyone help ?

 

Thanks, Fred

VE3WN / VE3PIE

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