I am going to do a simple SIMPLEX all-star node, using the URIx USB radio interface, which I just got. I have a Kenwood TM-241A transceiver.

I was told the speaker out jack is not sufficient:

The goal is access to output not influenced by the radio squelch or volume controls.

I was also told that there are high-pass filters in many radios which will eliminate most CTCSS, so I can't use the CTCSS_DET pin.

Does the Kenwood tm-241a have a place in it I can find with discriminator out, which I could solder some audio wires to?

  • $\begingroup$ I don't know about that specific radio, but usually this sort of thing is found on a TNC interface. It might reference "9600 baud" in some way, because 9600 baud TNCs have similar requirements. Look for a round, mini-din connector. $\endgroup$ Apr 9, 2014 at 12:21
  • $\begingroup$ Just skimming through the manual and images I can find on Google I couldn't find any clear illustration of such a port on that particular radio. Is there anything on the back or sides labeled "TNC" or "DATA" or "PACKET"? $\endgroup$ Apr 9, 2014 at 12:30
  • $\begingroup$ @PhilFrost Having two of those radios in my junk pile, I can confirm that there is only an Audio Out jack. $\endgroup$
    – W5VO
    Apr 10, 2014 at 14:08
  • $\begingroup$ I know there is only Audio Out on the OUTSIDE of the radio, but I am wondering if there is a Test point or something Directly from the Discriminator. I Don't care if I have to solder a tiny wire to a surface mount component, all radios operate on a basic principal, and there should be a place before the audio amp&filter. $\endgroup$
    – Skyler 440
    Apr 10, 2014 at 23:50
  • $\begingroup$ Does anybody here know if it will just work with audio out? All I am mainly worried about is picking up CTCSS tones. I can just turn the squelch off, and turn the volume knob to a certain level (or even solder a fixed resistor and disable the knob) and just hook her up. Even If I have to use a AF attenuator $\endgroup$
    – Skyler 440
    Apr 10, 2014 at 23:53

1 Answer 1


Typically a good place to get discriminator audio is the "high" end of the squelch control. Unfortunately the TM-241A does not have a conventional squelch control, making it necessary to tap onto the board itself. Pin 9 of IC1, an MC3372, is the output of the discriminator. If you can locate and solder to this pin it should give you the desired signal. If at all possible you should check the signal with a scope before soldering to it.


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