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RE: [wsjtgroup] Re: What causes multiple JT9-1 transmissions +/- 120 Hz?

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  • JC N4IS
    Hi Julian It count not be the case but, most of the modern radio uses an A/D right in front of the microphone. All functions like Volume, Vox, Compression
    Message 1 of 5 , May 12, 2013

      Hi Julian

       

      It count not be the case but, most of the modern radio uses an A/D right in front of the microphone. All functions like Volume, Vox, Compression ,Equalization, Modulator, and RF filter are actually software.

       

      If the audio from the PC is injected on the MIC connector it is possible to overload the A/D. These new radios does not have a real filter for RF, like the IC7600 and several others. As a result you can transmit  actual signals in several frequencies.

       

      A friend of my had this problem and he was trashing 160m band with signals each 5 KHz, 8 below and 8 above 1840. Moving the audio to the data port ,matching audio level, the carriers gone away and he has a clean signal now.

       

      The solution is always to use the data port and avoid to overload the A/D.

       

      Regards

      Jose Carlos

      N4IS

       

      From: wsjtgroup@yahoogroups.com [mailto:wsjtgroup@yahoogroups.com] On Behalf Of g4ilo
      Sent: Sunday, May 12, 2013 6:41 AM
      To: wsjtgroup@yahoogroups.com
      Subject: [wsjtgroup] Re: What causes multiple JT9-1 transmissions +/- 120 Hz?

       

       

      This is a common problem. It's either ripple from the power supply amplitude modulating the transmitted signal or hum on the input to the sound card doing likewise. Over here we see duplicates at +/- 100Hz as we have 50Hz mains in Europe.

      In my case the duplicates are around 40dB down on the main transmission so I only see it on stations stronger than +10dB. As this difference is fairly consistent on all very strong signals I suspect it is on the receive side. In your case the duplicates are only 20dB down so if it's not the transmitter check the isolation between transceiver and computer.

      Julian, G4ILO

      --- In wsjtgroup@yahoogroups.com, "n7jfp" <n7jfp@...> wrote:
      >
      > Maybe someone has seen this happen. I just had a WSJT-X JT9-1 QSO on 20m WA to HI. His transmissions had a +120 Hz and a -120 Hz duplicate transmission. What can cause this. I have not seen this before. The QSO window did not display the duplicates.
      >
      >
      > 2344 -2 0.6 1539 N7JFP NH7WN 73
      >
      > 2344 -20 0.7 1130 CQ EI7GSB IO52
      > 2344 -10 0.5 1214 CQ W6SZ DM14
      > 2344 -1 -0.2 1279 NH7WN W4EG R-10
      >
      > 2344 -22 0.6 1419 N7JFP NH7WN 73
      > 2344 -22 0.6 1660 N7JFP NH7WN 73
      >
      > 73,
      > Lawrence
      > N7JFP
      >

    • Joe Subich, W4TV
      ... Most rigs have an analog preamplifier immediately after the mic input. There are several issues in these designs. First is that most of the designers
      Message 2 of 5 , May 12, 2013
        > It count not be the case but, most of the modern radio uses an A/D
        > right in front of the microphone. All functions like Volume, Vox,
        > Compression ,Equalization, Modulator, and RF filter are actually
        > software.

        Most rigs have an analog preamplifier immediately after the mic input.
        There are several issues in these designs. First is that most of the
        designers attempt to put RF filtering (an RF choke) in the return lead
        of the mic which actually increases sensitivity to common mode RF and
        hum. Second is that the mic audio connections often run a significant
        distance from the connector to the preamp and the return is not
        connected to common *at the shield (case)* which again is not proper
        design. Finally, the preamp has a fixed gain - it is designed for
        the level of the manufacturer's microphone.

        In transceivers designed for dynamic microphones - Elecraft, Kenwood,
        Ten-Tec and Yaesu - that preamp is designed for signal levels in the
        5 mV range. In transceivers designed for electret microphones -
        Elecraft and Icom - that preamp is designed for signal levels in
        the 150 mV range. In either case the preamplifier will become a
        mixer if the input signals are more than one or two volts.

        > The solution is always to use the data port and avoid to overload the
        > A/D.

        The other solution - if one does not have a data port - is to use an
        attenuator of about 26 dB (10:1) between the sound card and microphone
        input. Quality sound cards produce a maximum undistorted audio level
        around 4.5 V p-p (~1.5V RMS) and the 10:1 attenuator will reduce the
        input to the preamp to about 150 mV maximum, preventing the preamp from
        becoming non-linear (mixing and/or clipping).

        73,

        ... Joe, W4TV


        On 5/12/2013 8:03 AM, JC N4IS wrote:
        > Hi Julian
        >
        >
        >
        > It count not be the case but, most of the modern radio uses an A/D right in
        > front of the microphone. All functions like Volume, Vox, Compression
        > ,Equalization, Modulator, and RF filter are actually software.
        >
        >
        >
        > If the audio from the PC is injected on the MIC connector it is possible to
        > overload the A/D. These new radios does not have a real filter for RF, like
        > the IC7600 and several others. As a result you can transmit actual signals
        > in several frequencies.
        >
        >
        >
        > A friend of my had this problem and he was trashing 160m band with signals
        > each 5 KHz, 8 below and 8 above 1840. Moving the audio to the data port
        > ,matching audio level, the carriers gone away and he has a clean signal now.
        >
        >
        >
        >
        > The solution is always to use the data port and avoid to overload the A/D.
        >
        >
        >
        > Regards
        >
        > Jose Carlos
        >
        > N4IS
        >
        >
        >
        > From: wsjtgroup@yahoogroups.com [mailto:wsjtgroup@yahoogroups.com] On Behalf
        > Of g4ilo
        > Sent: Sunday, May 12, 2013 6:41 AM
        > To: wsjtgroup@yahoogroups.com
        > Subject: [wsjtgroup] Re: What causes multiple JT9-1 transmissions +/- 120
        > Hz?
        >
        >
        >
        >
        >
        > This is a common problem. It's either ripple from the power supply amplitude
        > modulating the transmitted signal or hum on the input to the sound card
        > doing likewise. Over here we see duplicates at +/- 100Hz as we have 50Hz
        > mains in Europe.
        >
        > In my case the duplicates are around 40dB down on the main transmission so I
        > only see it on stations stronger than +10dB. As this difference is fairly
        > consistent on all very strong signals I suspect it is on the receive side.
        > In your case the duplicates are only 20dB down so if it's not the
        > transmitter check the isolation between transceiver and computer.
        >
        > Julian, G4ILO
        >
        > --- In wsjtgroup@yahoogroups.com <mailto:wsjtgroup%40yahoogroups.com> ,
        > "n7jfp" <n7jfp@...> wrote:
        >>
        >> Maybe someone has seen this happen. I just had a WSJT-X JT9-1 QSO on 20m
        > WA to HI. His transmissions had a +120 Hz and a -120 Hz duplicate
        > transmission. What can cause this. I have not seen this before. The QSO
        > window did not display the duplicates.
        >>
        >>
        >> 2344 -2 0.6 1539 N7JFP NH7WN 73
        >>
        >> 2344 -20 0.7 1130 CQ EI7GSB IO52
        >> 2344 -10 0.5 1214 CQ W6SZ DM14
        >> 2344 -1 -0.2 1279 NH7WN W4EG R-10
        >>
        >> 2344 -22 0.6 1419 N7JFP NH7WN 73
        >> 2344 -22 0.6 1660 N7JFP NH7WN 73
        >>
        >> 73,
        >> Lawrence
        >> N7JFP
        >>
        >
        >
        >
        >
      • JC N4IS
        Hi Joe ... The other solution - if one does not have a data port - is to use an attenuator of about 26 dB (10:1) between the sound card and microphone input.
        Message 3 of 5 , May 12, 2013
          Hi Joe
          >>
          The other solution - if one does not have a data port - is to use an
          attenuator of about 26 dB (10:1) between the sound card and microphone
          input.
          <<

          Old radios with no data port have XTAL filter on the RF to select LSB or
          USB, What it does is to limit any audio garbage inside the band pass of the
          XTAL filter. let's say < 2.7 KHz. Whoever if the A/D is overload on the new
          radios like IC7600 there is nothing to filter multiple transitions outside
          the band pass, I mean it is like you are transmitting a good signal on 10 or
          12 different frequencies 5 to 10 KHz apart. 1810. 1815.1820.1825. 1830 1835
          .... It is ugly.

          Regards
          JCarlos
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