[hpsdr] hpsdr/pandora grounding concept

[Giovanni Santin]

Hi Georg, on the link you can see how I planned to ground alex connectors on the front side : 
http://www.flickr.com/photos/john948/6914044792/
My plan was to solder the body of the bnc connectors to the copper plate, but gave up because I was afraid  the heat required was going to damage the alex boards.
I think that a bnc with the locking nut would have been much better choice for this project. 
Starting from the left, there are a pico-psu , metis, pennylane and mercury, all on a short version of atlas backplane. Then alex and pennywhistle, to be swapped with munin2 when I'll have time to build the kit.

73 de IZ0SQZ,   Giovanni
-----Original Message-----
From: Georg und Brigitte Prinz <getpri at t-online.de>
Sender: "Hpsdr" <hpsdr-bounces at lists.openhpsdr.org>Date: Sun, 05 Oct 2014 08:54:34 
To: John Ackermann N8UR<jra at febo.com>
Reply-To: getpri at t-online.de
Cc: hpsdr<hpsdr at lists.openhpsdr.org>
Subject: Re: [hpsdr] hpsdr/pandora grounding concept

***** High Performance Software Defined Radio Discussion List *****

Hi John,

thank you for the link. This refers to the inside of Alex. I did it
immediately  when I got Alex. The surface of the Alex enclusure consists
out of aluminium oxide which is a very bad conductor. Further more the
various parts of the enclusure are not screwed together. I suspect the
shielding is very good. Therefore I already think about putting the Alex
boards into a tin-box. But this action will be the last one.

The behavior of my system, and I wonder if I am the only one who
realized it, shows that there are interactions between the enclosure and
the individual components. 

The basic question is how do we ground the ATLAS board and the other
components of the transceiver correctly? 
I have no external ground connected to the enclosure. The plus and minus
of my external conventional power supply goes immediately through the
enclosure to the LPU-board ( I put a ferrite core on the cord outside
the box for test purposes only). The connections to ground Atlas are via
the 4/6 screws of the distance adapters.

On one side we are talking about sensitivity of more or less of -140dBm
and on the other side we have no clue about the electromagnetic
compatibility of our system.

Vy 73,

Georg,
DL2KP





Am Samstag, den 04.10.2014, 19:27 -0600 schrieb John Ackermann N8UR:
> Hi Georg -- here is a link to some work on grounding Alex in the Pandora enclosure; maybe the some comments will be helpful for your setup: http://www.febo.com/pages/hpsdr/alex/alex_grounding/index.html
> 
> 73,
> John
> 
> > On Oct 4, 2014, at 12:54 PM, Georg und Brigitte Prinz <getpri at t-online.de> wrote:
> > 
> > ***** High Performance Software Defined Radio Discussion List *****
> > 
> > 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
> > 
> > 
> > 
> > 
> > 
> > 
> > 
> > 
> > 
> > _______________________________________________
> > HPSDR Discussion List
> > To post msg: hpsdr at openhpsdr.org
> > Subscription help: http://lists.openhpsdr.org/listinfo.cgi/hpsdr-openhpsdr.org
> > HPSDR web page: http://openhpsdr.org
> > Archives: http://lists.openhpsdr.org/pipermail/hpsdr-openhpsdr.org/

-- 
Georg und Brigitte Prinz <getpri at t-online.de>

_______________________________________________
HPSDR Discussion List
To post msg: hpsdr at openhpsdr.org
Subscription help: http://lists.openhpsdr.org/listinfo.cgi/hpsdr-openhpsdr.org
HPSDR web page: http://openhpsdr.org
Archives: http://lists.openhpsdr.org/pipermail/hpsdr-openhpsdr.org/