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
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