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70281Re: What's the most TX power anyone has amplified an RXTX to? Just out of curiosity...

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  • irbsurfing
    Nov 21, 2012
      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.

      --- 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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