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[Linrad] Re: First real EME tests with MAP65-IQ

Hi Leif,

I made the changes you suggested and after setting the gain of the analog
hardware by -10 dB I got the noise floor in the main spectrum at 20 dB.

However, when I switch off the 144 MHz preamp. the noise floor drops only by
10 dB, not by 15 dB as it seems it should be.  What is the reason of this?

73. Gabriel - EA6VQ
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> -----Mensaje original-----
> De: linrad@xxxxxxxxxxxxxxxx [mailto:linrad@xxxxxxxxxxxxxxxx]En nombre de
> Leif Asbrink
> Enviado el: sábado, 28 de marzo de 2009 21:46
> Para: linrad@xxxxxxxxxxxxxxxx
> Asunto: [Linrad] Re: First real EME tests with MAP65-IQ
> Hi Gabriel,
> > First, the signal levels reported for the selected frequency
> > are between 3 and 5 dB weaker than with WSJT6.  I was running
> > MAP65 and WSJT6 in parallel and I could see that difference
> > for all signals. When a signal is, for instance, -22 dB in
> > WSJT6, the same signal is between -25 and -27 dB in MAP65.
> > When the band is noisy the difference is smaller (might be
> > 1 dB weaker in MAP65), possibly because of the excellent
> > noise blanker of Linrad.
> Try to set OL_RCF to 5 instaed of 6. (You may edit par_sdr14)
> That will increase the signal level by 6 dB. Set the first FFT
> amplitude to 1000 (default in Linrad) and adjust the gain of the
> analog hardware to place the noise floor in the main spectrum
> at 20 dB. You may use the gain setting in the frequency control
> box.
> Then verify that the noise floor drops by at least 15 dB when you
> switch off the DC power to your 144 MHz preamp.
> The green bar in the high resolution graph should now be about
> 6 dB above the thin red line. I think that is a bug in Linrad
> (I did not verify how the noise computation was normalized in
> a single channel system)
> With these changes you should see the same S/N reports in
> MAP65-IQ and in WSJT6 when both systems are run without
> a noise blanker.
> > Finally, near the moonset the band was really noisy
> > and I noticed that some signals that were clearly
> > visible in Linrad's waterfall were not visible at all
> > in MAP65's waterfall, and it did not decode them either.
> > Anyway this was only in very noisy conditions, due
> > to power lines.
> Once you have corrected the signal levels and verified
> that preamp on/off affects the noise floor as expected
> while your antenna points towards quiet sky, please make
> a wideband recording with Linrad next time you have really
> bad power line noise.
>   73
>     Leif
> >

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