70281Re: What's the most TX power anyone has amplified an RXTX to? Just out of curiosity...
- Nov 21, 2012Hello 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 email@example.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.
> 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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