RadioBanter - View Single Post

June 11th 06, 03:16 PM posted to rec.radio.amateur.antenna

wrote:
Try this test, wire a small 2.5 MHh RF choke across your antenna and
check the before and after noise levels. They will not change.

Cecil Moore wrote:
Obviously a false statement based on limited knowledge and
experience.

When did you do that test?

Around 1990 to cure the arcing at the coax connector
during clear-sky high-wind conditions in the Arizona
desert. When I got rid of the coax and used ladder-line
all the way to the tuner, I discovered that the 4:1 balun
in the MFJ tuner accomplished the same anti-arcing function
so hams using ordinary 4:1 voltage baluns are equalizing
that charge before it can arc.

When did you compare other antennas, like noise on plummer's delight
antennas?

The noise was the arcing of the coax connector at the input
to my IC-745 which woke me up at night and scorched my rug
after I disconnected it and laid it on the floor. Seems
obvious that going from arcing to not arcing changes the
noise level. I was afraid to turn the transceiver on during
the arcing process. If I had known I was ever going to have
this conversation with a doubting Thomas, I would have hung
an o'scope on it. The condition is well known to most desert
hams but I had just moved there from Silicon Valley. I never
experienced the condition in Silicon Valley or East Texas.

Installing the RF choke across the antenna feedpoint
cured the problem. I'm not talking about plumber's delight
antennas here. I am discussing Yagis and other antennas
whose driven elements are center-fed dipoles where there
is no DC path between the driven elements.

How many Yagi's have floating driven elements without ground paths?

It only takes one red car to disprove the assertion
that all cars are white.

All the Yagis that I have built used isolated dipole
elements and it only takes one to demonstrate the clear-
sky high-wind noise problems in the Arizona desert. Every
Arizona desert ham running bare isolated HF elements with
no DC path to ground will encounter the problem sooner or
later. The problem has been discussed here on this
newsgroup in the past, possibly while you weren't
reading it. As I remember, one ham solved the
problem with a 10K 3 watt carbon resistor across the
feedpoint.

It seems apparent to me that the problem occurs in very
low humidity conditions. That would include dust and
dry-air snow. And the dust doesn't have to be visible to
the naked eye. I've seen it happen with clear-sky and
seemingly clear-air conditions with high winds and low
humidity. I suspect dust/pollen particles too small to
see still carry a dry-air charge.
--
73, Cecil http://www.qsl.net/w5dxp