Posted by
Jim Brown-10 on
Mar 23, 2011; 6:50pm
URL: http://elecraft.85.s1.nabble.com/K3-Noise-from-P3-tp6201047p6201489.html
On 3/23/2011 10:54 AM, Ron D'Eau Claire wrote:
> If it's not being picked up by the antenna there must be some other path
> into the K144XV perhaps through an open ground between units, etc.
A Pin One Problem on either end of the BNC or power cables (that is, at
the P3 or K3) could couple around the antenna. In chasing RF noise
coupled from a noisy SteppIR power supply, I'm chasing exactly such a
coupling mechanism that is quite strong on 12M. At this point, I'm not
CERTAIN that the K3 has a Pin One problem on its power connector and
accessory power connector, but tentative results suggest it -- chokes on
those cables reduces the noise!
What does this mean from a circuit design point of view? The V+ AND V-
lines should both be RF bypassed to the chassis, AND should have a choke
between those conductors and interior circuitry. The V- conductor is
the one most usually overlooked. What RFI guru Henry Ott calls "the
hidden schematic lurking behind the ground symbol." Of course, the BNC
connector shells should be solidly screwed to the shielding enclosure at
both ends.
Note that this sort of problem might also be caused by an open shield on
the coax running between the P3 and the K3. I have two P3s. The BNC
cable shipped with one of them was bad.
73, Jim K9YC
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