Hello Wolf!

I guess it is what you call a "Soundcard-based SDR....
YU1LM-design: DR2B

Basically it works very well and the Mirror Frequency rejection is at
least 60db without using SPecLabs optimizations. When using this it can
be brought up to 80db and more but I found that this depends on the
level setting of the line input.

When you move the slider of input level just a little bit, the settings
of SpecLab will not be proper any more and image rejection falls back to
a lower value. (Could be soundcard related).
You have to retune the settings in SpecLab again for every particular
setting of the input level.

Because I use a sharp filter on 137 and a mixing QRG of 132kHz, any
signal on ~126khz is attenuated so much that it doesn't affect the
spectral analysis. At least I found nearly no difference between the
Mono-setting and the I/Q input-setting.

73
OE3GHB
Gerhard



Am Donnerstag, den 28.10.2010, 18:21 +0200 schrieb wolf_dl4yhf:
> Hello Gerhard,
> 
> you wrote:
> >
> > Today I swapped the RX of my grabber to SDR and the antenna to a
> > PA0RDT-design. I also did some minor changes to my grabber-page.
> >
> > (..)
> > I do not use a I/Q-setup, though the RX is I/Q. I found out that for
> > QRSS3 and QRSS60, the difference is minor and I/Q setup just uses a lot
> > more processor time.
> >
> > Any comments/reports are welcome.
> >
> 
> What kind of SDR are you using, SDR-IQ or Perseus ? (guess not one of 
> the soundcard-based SDRs).
> For the SDR-IQ, the CPU usage can be greatly reduced if you do run the 
> radio at the lowest possible sampling rate, which of course requires to 
> run it in true I / Q mode (and also the spectrum analyser).
> This greatly reduces the CPU load, because the PC software doesn't need 
> to run at very large sampling rates, instead the complex decimation will 
> be done in the SDR's FPGA or digital downconverter.
> 
> Especially when running on a laptop this can save some power, and (here) 
> completely eliminates the noise from a Thinkpad's internal cooling fan.
> 
> 73,
>     Wolf  DL4YHF .
> 
> 

DR2B HF SDR RECEIVER-YU1LM.pdf
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