[Elecraft] Background Noise with Mike Plugged in to Rear, , Mike Jack

[Victor Rosenthal 4X6GP]

In my experience, the single most important factor in reducing RFI 
problems is to prevent RF from flowing back into the station via common 
mode current on the feedline. This is easiest to do with balanced 
antennas. If they are coax-fed, then you need the appropriate choke at 
the feedpoint. And if the coax does not run perpendicular to the 
antenna, then a choke will probably be required at the entry to the 
shack as well.

Balanced antennas fed with balanced line like window line or open wire 
line work best with true balanced antenna tuners. The common practice of 
feeding a balanced line running a high SWR via an unbalanced tuner and a 
balun is less efficient both from the standpoint of power loss (the 
balun gets hot) and choking efficiency (the common mode current gets 
through).

An inherently unbalanced antenna, like an OCF dipole, also requires 
choking, but the demands on the choke(s) are higher.

RFI problems will vary according to the lengths of the feedlines and the 
band in use. A system that is clean on one band may be dirty on others 
if common mode currents aren't suppressed.

The time to apply ferrites is AFTER you have done the best possible job 
of reducing common mode currents, and after all your equipment is bonded 
together. I found that bonding my metal operating desk to the system helped.

73,
Victor, 4X6GP
Rehovot, Israel
CWops #5
Formerly K2VCO
https://www.qsl.net/k2vco/

On 26/11/2021 9:25, JR wrote:
> Re - Bob, K4TAX,  on whether to use ferrite beads to solve station 
> issues ...
> _______________________________________
> 
> Several years ago, when I was a new ham, Bob K4TAX encouraged me to 
> solve RFI/EMI and other issues, instead of populating the station with 
> ferrite beads, and this admonition has served me well ever since. Rather 
> than toss toroids at a problem, I diligently determine the exact cause 
> and fix it.  Sometimes it is something simple, such as routing a 
> microphone and computer cables away from, and not parallel with, coax 
> patch cables.  One time, it was as simple as cinching a coax connector 
> up tight.   As an ersatz musician, I have a pile of audio and recording 
> gear along with my ham station in the shack, and I suffer no issues on 
> any front.  All too often, hams claim the problem is "RF in the shack" 
> and toss ferrite toroids on every cable in the place, which masks or 
> conceals, but does not solve, the problem.   Thanks, Bob, for pushing me 
> to locate the real problem every time.  Do whatever diligence is due 
> under the circumstances, and you will surely have better results.   K8JHR