[hpsdr] Jan/Ozy Spurious Signals

[Joe Barger]

First, a big thanks to all the people responsible for getting the HPSDR so 
far so fast.  Amazing!

I've got the Janus/Ozy/Atlas combo with a Pico PS running.  Attached is a 
picture with nothing attached to the Janus inputs, the USB and SDR1000 
parallel cable connected to the Ozy, sampling at 96K, SDR1000 off.  The 
absolute level probably isn't calibrated real well in these tests, but the 
relative levels are what I'm interested in right now.  There are strong 
spurious spikes, as can be seen in the picture.  Switching SR on and off 
moves the spikes some as expected, but has no effect on the level.  I can't 
find any other SDR1000 control that affects the spikes significantly.

If I switch to the D44 card under the same conditions (nothing on the D44 
inputs, 96K sampling), there are no strong spikes (second picture).

It seems to me there's something in my Janus/Ozy/Atlas setup causing these 
spurious spikes since Athi's pictures under similar conditions are very 
clean and when using the D44 there are no spurious spikes.

When I connect all the inputs and run the SDR1000 everything seems fine 
except there is a hump in frequency response centered in the middle of the 
sampling range (see third picture).  The hump is even more pronounced when 
sampling at 196K.  The D44 shows a much smaller hump (see fourth picture).

Anyone got some idea's about what's going on and how to fix the spurious 
spikes and the hump?

Thanks

joe n6kk 
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