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Re: [softrock40] Re: What's the most TX power anyone has amplified an RXTX to? Just out of curiosity...

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  • Alan
    ... Subject: [softrock40] Re: What s the most TX power anyone has amplified an RXTX to? Just out of curiosity... ... Yes, I also have noticed variations in
    Message 1 of 19 , Nov 16, 2012
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      ----- Original Message -----
      Subject: [softrock40] Re: What's the most TX power anyone has amplified an RXTX to? Just out of curiosity...


      >I am a little concerned however about doing it with reduced drive level. I use cheap USB or built in audio cards (walking carefully
      >here..... don't want to restart THAT war)... and I have found that the channel to channel levels do not always track that well as
      >you change the overall level. So the relative audio gains at the reduced level may not be the same when you bring the drive back up
      >and, as a result, your image rejection at operating level may suffer.
      >

      Yes, I also have noticed variations in gain between channels as the volume slider, or drive slider is changed.
      Image rejection needs to be finally adjusted with these controls set for operation at maximum required output.

      I as hoping that when I tested it would not be necessary to reduce TX output. And wondering if there was a way to even further
      reduce the stray signals getting into the receiver.
      But it will be a while before I try.

      73 Alan G4ZFQ
    • irbsurfing
      Hi Chris, As well as ensuring that the image rejection is adjusted correctly you need to be sure that your soundcard is not emitting significant broadband
      Message 2 of 19 , Nov 20, 2012
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        Hi Chris,
        As well as ensuring that the image rejection is adjusted correctly you need to be sure that your soundcard is not emitting significant broadband noise.

        My setup uses an EMU USB0202 familiar to many, it works well on Rx but on Tx its noise floor is terrible, it has a high noise peak at about 10kHz which will modulate the QSE and give you strong noise peaks on each side of your carrier. Even playing music with good speakers you can hear a hiss (it might be faulty of course!).
        It measures about 20dB worse than an FT-817 in 2.7kHz BW at a 10kHz offset and consequently as it stands I would not use it on the air at all, let alone amplified to the legal limit!
        To fix it I had to change the capacitors in the QSE and add another pole of filtering. Then it was just about acceptable. It really requires some outboard filtering also. Flex Radio had issues like this in the early days and I recommended a filter in the lead from the sound card, the document is still available from their website.
        Not sure how other cards compare but I'm sure that the Delta44 for example, is much better in this respect. If you have a USB0202 find a way to check it first before going on the air!
        Andrew
        G4XZL

        --- In softrock40@yahoogroups.com, Chris Wilson <chris@...> wrote:
        >
        >
        >
        > >
        >
        > > ----- Original Message -----
        > > Subject: [softrock40] Re: What's the most TX power anyone has
        > > amplified an RXTX to? Just out of curiosity...
        >
        > > Another related question may be "What is the largest spurious
        > > signal transmitted from a Softrock, (or other SDR)."
        >
        > > On WSPR "Chat" the other day I came across someone who was
        > > transmitting without having checked his TX IQ was correct. Transmitting
        > > on the wrong frequency.
        > > He also knew nothing about setting TX IQ balance so when the IQ was
        > > set correctly his image may have been only 25dB down.
        > > If he had a fault he could have been transmitting simultaneously on
        > > both frequencies without knowing. The same as "mirrored"
        > > receiving.
        >
        > > A good understanding of what is involved is necessary before
        > > amplifying mistakes. Any soundcard SDR transmitter needs careful
        > > setting by someone who at least understands the basics. A receiver must be used to check.
        >
        > > I sometimes wonder when immediately after building a Softrock
        > > somebody says "I want more power". It took me quite a while to get a
        > > fair understanding of the Softrock and software.
        >
        > > 73 Alan G4ZFQ
        >
        >
        >
        >
        > 16/11/2012 14:36
        >
        > As I said, I was just curious as to how much power people
        > realistically run from these things, and my thoughts were whether they
        > could be made clean enough to be unobtrusive at high power output
        > levels, or whether the fact the majority are QRP tends to hide any
        > nasties from the fellow spectrum users. Is a soundcard based SDR TX
        > bound to be dirtier than a good conventional transmitter? Or can the
        > Softrock RXTX package be amplified to serious levels without becoming
        > unsociable, and without major doctoring?
        >
        > --
        > Best Regards,
        > Chris Wilson. 2E0ILY
        >
      • Alan
        ... Subject: [softrock40] Re: What s the most TX power anyone has amplified an RXTX to? Just out of curiosity... ... Andrew, If it is your 0202 and not
        Message 3 of 19 , Nov 20, 2012
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          ----- Original Message -----
          Subject: [softrock40] Re: What's the most TX power anyone has amplified an RXTX to? Just out of curiosity...


          >
          >
          > Hi Chris,
          > As well as ensuring that the image rejection is adjusted correctly you need to be sure that your soundcard is not emitting
          > significant broadband noise.
          >
          > My setup uses an EMU USB0202 familiar to many, it works well on Rx but on Tx its noise floor is terrible, it has a high noise peak
          > at about 10kHz which will modulate the QSE and give you strong noise peaks on each side of your carrier.

          Andrew,

          If it is your 0202 and not anything else then it must be faulty.
          Many use that, I'm sure it would have been mentioned by now.
          Here http://g4zfq.alotspace.com/RightMarkTests/E-MUTrackerPre%20_%20USB192.htm is my test on a Tracker Pre. This is basically a 0202
          with preamp, not used of course.

          A soundcard must be bad to seriously affect a transmit signal. As long as it is not overdriven I would expect noise and hum to be
          well below the signal level.

          73 Alan G4ZFQ


          Even playing music with good speakers you can hear a hiss (it might be faulty of course!).
          > It measures about 20dB worse than an FT-817 in 2.7kHz BW at a 10kHz offset and consequently as it stands I would not use it on the
          > air at all, let alone amplified to the legal limit!
          > To fix it I had to change the capacitors in the QSE and add another pole of filtering. Then it was just about acceptable. It
          > really requires some outboard filtering also. Flex Radio had issues like this in the early days and I recommended a filter in the
          > lead from the sound card, the document is still available from their website.
          > Not sure how other cards compare but I'm sure that the Delta44 for example, is much better in this respect. If you have a USB0202
          > find a way to check it first before going on the air!
        • irbsurfing
          Hello Alan, Well, as I said mine might be faulty! I was shocked at how bad it was. I will try running the Rightmark Analyser and see how it compares to your
          Message 4 of 19 , Nov 21, 2012
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            Hello Alan,
            Well, as I said mine might be faulty! I was shocked at how bad it was.
            I will try running the Rightmark Analyser and see how it compares to your Tracker Pre, thanks for posting the links. I will report back.
            Thanks,
            Andrew

            --- In softrock40@yahoogroups.com, "Alan" <alan4alan@...> wrote:
            >
            >
            > ----- Original Message -----
            > Subject: [softrock40] Re: What's the most TX power anyone has amplified an RXTX to? Just out of curiosity...
            >
            >
            > >
            > >
            > > Hi Chris,
            > > As well as ensuring that the image rejection is adjusted correctly you need to be sure that your soundcard is not emitting
            > > significant broadband noise.
            > >
            > > My setup uses an EMU USB0202 familiar to many, it works well on Rx but on Tx its noise floor is terrible, it has a high noise peak
            > > at about 10kHz which will modulate the QSE and give you strong noise peaks on each side of your carrier.
            >
            > Andrew,
            >
            > If it is your 0202 and not anything else then it must be faulty.
            > Many use that, I'm sure it would have been mentioned by now.
            > Here http://g4zfq.alotspace.com/RightMarkTests/E-MUTrackerPre%20_%20USB192.htm is my test on a Tracker Pre. This is basically a 0202
            > with preamp, not used of course.
            >
            > A soundcard must be bad to seriously affect a transmit signal. As long as it is not overdriven I would expect noise and hum to be
            > well below the signal level.
            >
            > 73 Alan G4ZFQ
            >
            >
            > Even playing music with good speakers you can hear a hiss (it might be faulty of course!).
            > > It measures about 20dB worse than an FT-817 in 2.7kHz BW at a 10kHz offset and consequently as it stands I would not use it on the
            > > air at all, let alone amplified to the legal limit!
            > > To fix it I had to change the capacitors in the QSE and add another pole of filtering. Then it was just about acceptable. It
            > > really requires some outboard filtering also. Flex Radio had issues like this in the early days and I recommended a filter in the
            > > lead from the sound card, the document is still available from their website.
            > > Not sure how other cards compare but I'm sure that the Delta44 for example, is much better in this respect. If you have a USB0202
            > > find a way to check it first before going on the air!
            >
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