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DX394 audio response

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  • David Griffin
    A discussion came up a few weeks ago about using the radio for SW fax and rtty. My DX394 was across the room at the time but is now installed within reach of
    Message 1 of 3 , Jul 1, 2005
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      A discussion came up a few weeks ago about using the radio for SW fax and rtty.  My DX394 was across the room at the time but is now installed within reach of my audio equipment and PC, so I hooked it up yesterday and am now enjoying even better AM audio thanks to the use of an equalizer and the SR5 audio processor running my sound card (auto notch on SW BC !!)   Not that all that is really needed for AM since I've always thought the 394's audio was terrific "right out of the box" when connected to a larger speaker.
      However.....measuring with Winscope (Oscilloscope for Windows 2.51),  the audio response of the receiver seems to really roll off above 1800 hz.   When I run MSCAN Meteo and SEATTY,  they definitely do not like the audio signal, preferring to decode with black and white at around 1500 and 2350 hz. 
      And yet, the consensus as I remember it was that the DX394 performs admirably on FAX and RTTY.
      So what am I doing wrong?  Other than the purple wire, the only other mod I have performed on the radio is the one where I added a capacitor or two (sorry, it's been a while) to reduce the ridiculously wide bandwidth as the radio was shipped, but it's hard to believe that the mod reduced the bandwidth that much.  Did it?   Hard to believe since AM voice has enough highs and is quite intelligible.
      Dave
      N2chi
    • Jara
      Hi David, I dont know that I understand all, because I speak english a little. I use DX394 for fax and sstv, rtty etc. too. But signal from tape output is for
      Message 2 of 3 , Jul 9, 2005
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        Hi David,

        I dont know that I understand all, because I speak english a little.
        I use DX394 for fax and sstv, rtty etc. too. But signal from tape
        output is for some audiocards poor. I use 1 transistor as audio
        preamplifier. (Signal from tape output is good for my old PC but is
        not good for notebook or laptop.)
        I have not problems now.
        I use: Radioraft with hamcommodem, and with audiocard also JVFAX,
        MMSSTV, MMTTY, Skysweeper, Hoka Code, and also programs for HFDL, also
        Selcal, Hamscope or MixWin.
        Program for VHF ACARS (with external converter VHF/HF for DX394) too.
        And: I use I think all mods for DX394 in my receiver...

        Best regards, Jara "Rat"

        Maybe it is wrong ground: maybe you have a "ground loop" ??
        You can try use only notebook or laptop with accumulators, not power
        net.
      • David Griffin
        Hi Jara, Thanks for your response. Sounds like the Dx394 is performing well for you and the variety of decoding software you are using. Grounding seems OK
        Message 3 of 3 , Jul 10, 2005
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          Hi Jara,
          Thanks for your response. Sounds like the Dx394 is performing well for you
          and the variety of decoding software you are using. Grounding seems OK
          here and I don't have any problems with other radios when decoding wefax,
          etc. I have been playing with the setup a bit and have realized that the
          394 seems to work better for me when I use very close filtering such as with
          the SR 5 software. In fact, today I got a pretty good fax on 10.534 from
          Halifax after I realized that I had SR5 set to filter the audio I hear, but
          not the audio going to the decoder program.
          Dave

          > Hi David,
          >
          > I dont know that I understand all, because I speak english a little.
          > I use DX394 for fax and sstv, rtty etc. too. But signal from tape
          > output is for some audiocards poor. I use 1 transistor as audio
          > preamplifier. (Signal from tape output is good for my old PC but is
          > not good for notebook or laptop.)
          > I have not problems now.
          > I use: Radioraft with hamcommodem, and with audiocard also JVFAX,
          > MMSSTV, MMTTY, Skysweeper, Hoka Code, and also programs for HFDL, also
          > Selcal, Hamscope or MixWin.
          > Program for VHF ACARS (with external converter VHF/HF for DX394) too.
          > And: I use I think all mods for DX394 in my receiver...
          >
          > Best regards, Jara "Rat"
          >
          > Maybe it is wrong ground: maybe you have a "ground loop" ??
          > You can try use only notebook or laptop with accumulators, not power
          > net.
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