[Elecraft] Common Mode chokes to reduce noise

[David Gilbert]

I don't see how a common mode choke would help in that situation. If the 
noise changes that dramatically depending upon where you have the 
antenna pointed, that strongly suggests that the noise is being received 
by the antenna and is not riding on the shield of the coax.  If it is 
received by the antenna it is differential in nature and a common mode 
choke won't do anything.

It sounds like you are being plagued by either a local noise source, or 
the atmospheric noise is much stronger in one direction.  In my case, 
the background noise during the middle of the day is always stronger 
east versus west even though there isn't any significant housing or 
businesses within 200 miles east of me.

73,
Dave   AB7E



On 11/27/2021 10:21 AM, Ed Cole wrote:
> I primarily work eme so band noise is a prime enemy of weak signals.
>
> I was reading the comments about combating mic noise and wondered if 
> adding some ferrite beads to my 6m coax at the shack would have any 
> effect on received broad-band noise.  I definitely see the noise peak 
> in one direction of the antenna S5/S7 vs S2 at 180-degrees azimuth 
> rotation, and it also drops with about 13 degrees of antenna elevation.
>
> My 6m LFA antenna use ferrite bead baluns.  Transmission coax runs 
> 40-foot vertical and 50-foot horizontal on the ground.  Rx comes from 
> a remote preamp connected thru a TR relay with output thru LMR-240 
> coax to the Rx antenna port of the K3.
>
> 73, Ed - KL7UW