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Power Supply Noise

To: <tentec@contesting.com>
Subject: Power Supply Noise
From: astaiano@midcoast.com (Andy Staiano)
Date: Mon, 25 Nov 1996 12:01:18 -0500 (EST)
Noise Problem


On November 4th I ordered a Mod. 555 Scout Transceiver, a Mod 938
power supply (Ten-Tec no longer stocks the unit but they had a
few demo units available) and three band modules.  All arrived in
good condition from the factory some days later.  

I'm very pleased with the Scout except for a high noise level. 
Broad band noise that sort-of moves around the band with a level
from S-5 to S-8 usually.  Initially  searched for a noise source
in the house but eventually I found the noise source is
the Mod 938 switch-mode power supply.  When I powered the Scout
from a conventional 12 volt power supply I had NO noise.  That
will solve the problem for use at home but I bought the mod. 938
supply because it's light and intended to use it when I take the
rig on trips

Has anyone else experienced a noise problem with the Mod. 938
supply?  Has anyone come up with a correction?  I tried the
following without seeing any improvement:
1.   Wrapping the output leads around a ferrite core.

2.   Wrapping the ac line around a ferrite core.

3.   Bonding the power supply steel case to the transceiver
     ground.


Andy Staiano, W1CR  astaiano@midcoast.com


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