Antennas like the OCFD, EFHW , really
even a plain dipole will utilize the coax shield as part of the
antenna's counterpoise if they can, resulting in RF in the
shack, excessive noise pick-up, and pattern distortion. The EFHW
requires a counterpoise of ~10% of the main element length, the
others not so much.
The way to prevent this problem is a
choke unun at the antenna feedpoint. This can be as simple as
several turns of coax in 8 to 12 inch loops, or at qrp levels
several turns of RG-174 wound around something like a FT240-43
I had a Balun Designs 2KW Unun that was
the center of a 160/80 trap dipole, after a few years the
electrical box it was mounted in deterioated and it went to the
Recently it's "parts" have now been
resurrected and it now forms the input choke unun for my 4 core
49/1 EFHW transformer, all in the same 4x4x6 junction box.
Fighting RF in the shack problems never
ends until you find a way to keep it out.
73 Jack KZ5A
On 4/11/2019 1:44 PM, Joe Puma wrote:
I can try that on the short patch from tuner to meter or radio as
I have LM240 there. but the line going to antenna is RG213. So I
don’t have a clip ferrite that big.
On Apr 11, 2019, at 3:40 PM, Evan Hand <elhandjr@...
I had similar problems when connected to an
off center fed dipole. i solved my issues with clip on
ferrite on the coax going to the antenna. That may work
for you. Maybe a ferrite between the uBitx and the tuner,
or an isolation balun
The issue was RF on the braid of the coax.