[hpsdr] reducing computer radiated emissions

[ct1izu]

There are a number of sources for unwanted emissions in an HPSDR set. It 
gets complicated as everybody has a different physical layout.

The first line of defence is to have the Atlas Back Plane with OZY MERC and 
PEN in an enclosure with Tube Ferrites of 43 or similar material on ALL 
leads out of the enclosure.
ALL also  means the MIC and Headphone leads which will often run parallel 
with the Mouse cable in a typical system  ----yes been there----  and even 
the coax leads whose braids will bring in unwonted signals.

Next make sure the SMPSU in the computer is clean. Paying top dollar for a 
supply does not guarantee that its any better than a cheap unit. Lift the 
lid and check the PCB is fully populated. Many times you will find wire 
links across where input filters should be. Adding in the missing items is 
pretty simple using  one of the internet guides. You also need to add some 
1N and 10NF SMD caps between the ground output connection area and the 
various psu voltage  output line connection area. It may be necessary to use 
discrete caps on some of the traces if the span is too large. If possible 
also remove any unused  harness wire external to the supply to help  reduce 
radiation.

You might want to examine is you have the correct feed point for the OCD, 
the pattern can be pretty awful with pick up from the least desirble 
direction if you get it wrong!!

Shel CT1IZU

----- Original Message ----- 
From: "David McQuate" <mcquate at sonic.net>
To: <hpsdr at openhpsdr.org>
Sent: Tuesday, November 30, 2010 8:03 AM
Subject: [hpsdr] reducing computer radiated emissions


> ***** High Performance Software Defined Radio Discussion List *****
>
> My Core 2 Duo on a Gigabyte main board in a CoolerMaster case radiates all 
> sorts of junk, from somewhat noisy discrete signals to hash covering tens 
> of kHz, that changes when I move the mouse, and when the DSL modem / 
> router sends out ARP queries once a second.
>
> Mercury's input is by 20-feet of RG-58 coax, connected to a 4:1 toroidal 
> balun, open-wire feed-line and an off-center-fed dipole, one end of which 
> is, unfortunately, only about 20 feet from the computer.
>
> I've placed snap-around ferrites on the power cord, ethernet cable, 
> monitor cable, USB, keyboard & mouse cables, without noticeable 
> improvement.
> The ethernet cable is more than 100 feet long, the DSL modem being pretty 
> far from my shack.
>
> Have others solved this sort of problem?
> What did you do?
>
> Thanks!
> 73,
> Dave
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