[hpsdr] hpsdr/pandora grounding concept

[Georg und Brigitte Prinz]

Hi,


I built an enclosure similar to Pandora box for OZY, Mercury and Alex
out of aluminium sheets. The cards are powered by LPU and an external
analog power supply. The Atlas board is screwed to the box via 4
distance metal adapters. Two additional metal adaptors are placed in the
middle of the atlas board without screws. No other ground connection is
made to the box.

Now I realize that there are several spurs up to -114dBm and more with
side spurs +/-48 kHz. The noise floor is around -135dBm. Alex is
terminated with 50 ohms dummy. 
Another effect is, when shortening the BNC antenna-plug of mercury to
the enclusure, the spurs are about 10dB up. The connection to Alex is
still there.

If I open the enclosure (access plate on top and in front of the cards)
most of the spurs are down to the noise floor. 

I guess, that this is an grounding problem, in general. So far, I didn´t
see any discussion on this subject in the forum at all.

Did anybody else have similar appearances and how do you recommend to
ground all components inside the enclosure.


73,

Georg,

DL2KP