[Elecraft] Interesting K3 QRM problem

[Jim Brown]

On 10/23/2014 3:58 AM, Vic Rosenthal 4X6GP/K2VCO wrote:
> I have a BC band filter which is used with the MFJ antenna analyzer 
> when there are nearby BC signals. Sure enough, putting this in series 
> with the K3 ANT 1 connector kills the noise. Of course I can't 
> transmit through it. 

Hi Vic,

A few suggestions. First, try the BC Band filter on the K3 RX loop. If 
that works, work out a switching arrangement so that you can apply it to 
either antenna. Second, build or buy a BCB filter that can handle the K3 
output. Based on the frequency of the BCB transmitter, one of the lower 
cost filters should work. I've measured the vintage ICE BCB filter, and 
it's good for at least 40 dB on 1080.

Another thought is that this might be common mode on the coax, in which 
case a serious ferrite choke tuned to 1080 might help. I'd start with at 
least 20 turns of RG58 on a #31 2.4-in toroid, and I'd put it by the rig.

73, Jim K9YC