[Elecraft] [K3] Noise from P3

[Alan Bloom]

On Wed, 2011-03-23 at 19:35 -0700, Jim Brown wrote:
> On 3/23/2011 1:30 PM, John Lemay wrote:
> > Yes, I can "home in" on the noise with great certainty !
> 
> That indicates that the noise is being radiated by the P3 or something 
> attached to it, and picked up on your antenna (and not picked up on K3 
> wiring).

I can see the noise on mine if I hook a clip lead to the ANT3 (144 MHz)
connector and place it close to the display.  But I doubt you could hear
that on an external antenna.  The opening in the front panel is much
smaller than 1/2 wavelength on 2 meters, so the far field should be
greatly attenuated and the near field falls off rapidly with distance.

> The comments by others that ferrites on the power cable killed the noise 
> suggest that that cable is doing the radiating. Now, I wouldn't rule out 
> the coax as a radiator if someone has choked the power cable and still 
> heard noise -- with RFI, always assume that there could be more than one 
> coupling mechanism.

The shells of the coax and the RS-232 connectors are grounded directly
to the chassis.  Sounds like it must be the power cable.

Alan N1AL


> Again, let me emphasize that a ferrite core is a low Q parallel resonant 
> circuit. Most single #31 or #43 cores are, by virtue of their size and 
> shape, cause a single turn to resonate close to 2M, while more turns 
> move the resonance down to lower frequencies. This a problem on 2M is 
> better solved with multiple cores rather than multiple turns, whereas 
> problems on 6M are better solved with two turns and on the HF bands with 
> more turns.
> 
> 73, Jim K9YC
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