[Premium-Rx] Racal RA6790GM

[John USA]

Hi John,

Presumably, you've got the rx opened up to put thy finger on the memory 
chip;  this in itself invalidates your observations from a 
should-you-fix-it? point of view.  The single fact that the noise gets 
louder is probably due to your body acting as an antenna...you can observe 
this sort of thing, for example, when you hold a portable radio antenna or 
stick your finger against the center conductor of your antenna input (you 
may need a few inches of wire to connect your finger to the antenna input.

If you have this problem with the rx closed up and "installed" with antenna, 
etc, then you need to measure the level.  Depending on the frequency of 
observation and the level, this may be normal or not.  The radio being built 
from body parts, it's possible you have a loose screw or missing piece of 
shielding.

If you have a spectrum analyzer or scope, make a small nearfield probe (coax 
cable with a couple of 1" loops on the probe end) and search around the rx. 
If you find suspicious spots, and you may, then start investigating 
shielding strategies.

Any questions, drop a note to me.  I've done this stuff with a number of 
Cubic 3030 series stuff...works well.  Typical points of leakage are 
display, keypads, some connectors, etc.

good luck

John Collins
________________________________
----- Original Message ----- 
From: "John" <k9utk at one-eleven.net>
To: <premium-rx at ml.skirrow.org>
Sent: Monday, June 12, 2006 5:44 PM
Subject: [Premium-Rx] Racal RA6790GM


> Greetings group
> We have subj rec and enjoy it very much so plan to get another 
> (Frankenstein unit made from parts). Question is:
> In looking inside the rec and with the gain turned up, I hear some noise 
> that sounds like computer clock harmonics.  The rec has the A6 computer 
> interface boards and the noise I hear gets noticeably louder when I put my 
> finger on the memory chip packages and some of the other LSI packages on 
> the A6 boards.  Is this normal or do we have a problem???
>
> regards
> John
>
>
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