[Elecraft] Samlex 1223 & 1235 power supplies

[Jim Brown]

On Mon, 24 May 2010 07:57:25 -0400, Bill Coleman wrote:

>> Both power supplies are dead quiet, the fans seldom come on. They both sit
>> on top of the transceivers and never cause sperious 
>> interference.

>The SEC 1223 does generate some RF noise. This is most noticeable on 160m.

It is important to understand that sitting on top of the transceivers is 
NOT the primary interference coupling mechanism for RFI. Rather, noise is 
coupled out of the noise source external wiring (that is, the AC power cord 
and the DC power wiring), which then radiates it INTO YOUR RX ANTENNA. Noise 
sources can also radiate from INTERNAL wiring if they are poorly shielded, 
again picked up by your antenna. Physical proximity of the noise source to 
your rig has nothing to do with this process. What matters is proximity to 
your ANTENNA. Of course, if your antenna was a long wire that ends at the 
shack, it would hear a noisy power supply quite well. 

The only mechanism in which a noise source might couple by proximity to the 
rig is MAGNETIC coupling between a current loop and a rig that lacks magnetic 
shielding for its wiring. The K3 has poor magnetic shielding at AF, but is 
better at HF.  

73,

Jim K9YC