I have an old Alinco dual-band radio, the DR-600 (service manual) (manual)

I want to use this radio for receiving APRS packets. The speaker audio out Works but there are too many things to go wrong with Squelch, Volume knobs, or filter circuits designed for a speaker with a human ear which make a packet harder to decode with software.

I have looked through the service manual, but I don't really see anything that says "Discriminator" or "flat audio" on the schematic.

Where is the best place to pull audio for packet use on my Alinco DR-600 mobile transceiver? I would greatly appreciate pointers in the schematic to where I can test for audio sources.


You may actually want to use speaker out as it will most likely have the proper de-emphasis (6db/octave). Most APRS signals sent our are with pre-emphasis and tapping from your radio at the flat audio signal may actually do more harm than good.

Even with a dedicated port for audio out on your radio you probably still have to tune your TNC to the proper signal levels (deviation) anyway so you might as well hook it up to a cro and confirm all looks good.

  • $\begingroup$ Thanks. I actually built a TNC using a sound card with a pin as PTT driver, so I will still have to mess with levels to get a good signal to the computer, but I think the best option will be to remove the knobs and just go with speaker $\endgroup$
    – Skyler 440
    Jun 24 '15 at 0:23
  • $\begingroup$ That or use the socket for the microphone on the front of the radio. That way you also prevent mixing in any ambient audio from the hand mike on transmit. Did the soundcard thingy on Linux/RPi, seems to work quite well. My radio is an old Icom IC-P2AT. $\endgroup$
    – captcha
    Jun 24 '15 at 1:42
  • $\begingroup$ It seems to work pretty well, but if there is a bit of noise, it won't decode. Is that normal? $\endgroup$
    – Skyler 440
    Jun 24 '15 at 13:45
  • $\begingroup$ Here is a recording of some audio in. The first packet was NOT decoded and the second WAS amsatnet.info/recordings/APRS.mp3. That is what I found the noise thresold to be using soundmodem on linux. Is that normal? $\endgroup$
    – Skyler 440
    Jun 24 '15 at 13:52
  • $\begingroup$ I think you mean "deemphasis" where you're writing "deviation". $\endgroup$
    – Kevin Reid AG6YO
    Jun 25 '15 at 1:19

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