Hello all.
Had noise and zero spur (DC...) that were wide and strong (rendered a
swat of 2 khz not usable around the LO freq.)
Saw among the photos what N1RX did with a battery driven SR40 instead
of the USB % volt from the PC.
Connected a battery (through a voltage reg.) to the SR40 instead of the
USB connector and that made a much better S/N but not as good as the
one on the picture.(actually a wallwart floating supply is as good)
Then I disconncted the antenna (which is a trap vertival and not
floating) and found out that by just touching the screen the noise
grew, which is a clear indication of a ground loop.
Added an isolation transformer (actually a UNUN) made by threading 10 T.
of twisted enammeled copper wire throgh a small toroid and got rid of
the ground loop.
Now the zero(dc) spur is about -115dbm (which disappears in the band
noise in the afternoon) and very narrow so I get the whole range of
frequencies free and usefull.
Then to make it simpler and more permanent I cut a groove (with a
dremel) around the BandPass filter to isolate it from the SR40 and the
soundcard ground . That is as good as using the trafo.
You can see a photo on the photos section at Joe's folder.
73 de Joe
