From: Laurence KL7 L <hellozerohellozero@hotmail.com>
To: John Langridge <kb5njd@gmail.com>,
        "rsgb_lf_group@blacksheep.org"
	<rsgb_lf_group@blacksheep.org>
Thread-Topic: Noise - dont clean your shacks!
Thread-Index: AQHSE3qwNIenZtWrL0mMpx+MeV2afg==
Date: Tue, 20 Sep 2016 20:08:03 +0000
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Subject: LF: Noise - dont clean your shacks!
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One interesting thing about clean up of radio shacks and moving equipment a=
round is that you suddenly learn something is going on you really didn't kn=
ow about.


Aces high E probe (L400b)  has always had the best or concurrently equal pe=
rformance of all the arrays here but for the past 24 hours it had been down=
 a dB or two s/n wise


Thinking it was a decoupling issue I checked feeders, performance of amp, s=
plitters etc - and it wasn't till I realized I had put the die cast aluminu=
m fully sealed box which houses the power injector and cap/transformer atop=
 my computer that if I moved the box over the pressed steel lid of the comp=
uter we were getting induced magnetic noise coupled into the box causing a =
reduction of s/n.


 I could actually hear the difference on the R75 as I slide the box over th=
e top of the computer lid - the noise wasn't coming in common mode on coax =
or via the power injector cables.


The box had to be laying flat atop the computer press steel cover to induce=
 noise  - move it just 1 cm above and the coupling noise stopped.


So - lesson learned that Die Cast Aluminum boxes aren't perfect at magnetic=
ally induced fields - its not  shielded Mu metal!


Keep any coupling box or perhaps not perfectly screened/matched cables (min=
e didn't couple), away from sources of potential mag coupling noise generat=
ors -


...and don't clean up the shack as your radio performance will likely suffe=
r (just kidding!)


Laurence KL7L WE2XPQ

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<p>One interesting thing about clean up of radio shacks and moving equipmen=
t around is that you suddenly learn something is going on you really didn't=
 know about.</p>
<p><br>
</p>
<p>Aces high E probe (L400b) &nbsp;has always had the best or concurrently =
equal performance of all the arrays here but for the past 24 hours it had b=
een down a dB or two s/n wise</p>
<p><br>
</p>
<p>Thinking it was a decoupling issue I checked feeders, performance of amp=
, splitters etc - and it wasn't till I realized I had put the die cast alum=
inum fully sealed box which houses the power injector and cap/transformer a=
top my computer that if I moved
 the box over the pressed steel lid of the computer we were getting induced=
 magnetic noise coupled into the box causing a reduction of s/n.</p>
<p><br>
</p>
<p>&nbsp;I could actually hear the difference on the R75 as I slide the box=
 over the top of the computer lid&nbsp;- the noise wasn't coming in common =
mode on coax or via the power injector cables.</p>
<p><br>
</p>
<p>The box had to be laying flat atop the computer press steel cover to ind=
uce noise &nbsp;- move it just 1 cm above and the coupling noise stopped.
</p>
<p><br>
</p>
<p>So - lesson learned that Die Cast Aluminum boxes aren't perfect at magne=
tically induced fields - its not &nbsp;shielded Mu metal!
</p>
<p><br>
</p>
<p>Keep any coupling box or perhaps not perfectly screened/matched cables (=
mine didn't couple), away from sources of potential mag coupling noise gene=
rators -&nbsp;
</p>
<p><br>
</p>
<p>...and don't clean up the shack as your radio performance will likely su=
ffer (just kidding!)</p>
<p><br>
</p>
<p><br>
</p>
<p>Laurence KL7L WE2XPQ<br>
</p>
</div>
</body>
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