[hpsdr] QSD gain and noise.

[Robert McGwier]

I measured the Flex 5000A production model I have.  The MDS in 500 Hz at 
50.1 MHz is 6 dB worse than it is at 80 meters with preamp on.  Since 
the preamp defaults to on at 10 and 6 meters,  with the preamp off, the 
best I could do was compare at 80 meters and 12 meters.  The MDS was 1 
dB worse at 24 Mhz than it was at 3.5 MHz.

I do not understand where the notion that the noise floor in the 5000 
rises 20 dB from best to six meters.  I suspect that this was due to 
measurements we made in the SDR-1000.  It just isn't so.  There has been 
some discussion that there is some theory behind this.  It is faulty. 
The reason the noise rises in the 5000 is the choice of switch and this 
is perfectly born out by the measurements I just gave above.  The switch 
does begin to lose aperture above 24 MHz.

This is not a theoretical fault of the QSD.  It is a practical fault of 
the parts used from my measurements.

Bob
N4HY

-- 
AMSAT Director and VP Engineering. Member: ARRL, AMSAT-DL,
TAPR, Packrats, NJQRP, QRP ARCI, QCWA, FRC. ARRL SDR WG Chair
"If you're going to be crazy, you have to get paid for it or
else you're going to be locked up." Hunter S. Thompson

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