RadioBanter - View Single Post

June 11th 06, 04:20 PM posted to rec.radio.amateur.antenna

wrote:
People actually seem to think the little particles voving through the
air charge the antenna to a different potential than the air around the
antenna, and that a "dc" path to earth or "dc" path around an element
somehow magically stops RF noise.

Please don't accuse people of believing in magic until you
understand the physics involved.

There's no magic involved. Dry-air dust and snow particles
certainly can transfer a charge to an uninsulated wire in
the air. It is simple physics to realize that when a highly
charged particle touches a conductor, the charges between
the two objects will be equalized. It would be magic if the
particle and the wire did NOT equalize their charges by
transferring excess differential charge when they come
into contact.

Given a dipole where one element has a DC path to ground
and the other element is floating with respect to ground,
it is reasonable to expect the charge between the two
elements to be different and they often are. The difference
in charge will build up to the point where the smallest gap
between the two conductors arcs. In my configuration in
the Arizona desert, that gap existed at the coax connector
at the transceiver and it did indeed arc badly. It woke me
up and scorched my rug after I disconnected it from my
transceiver. The arc was bright enough to light up the
room and certainly caused RF noise. The wind was blowing
around 30 mph and there wasn't a cloud in the sky.

Given an extreme relative charge between the element with
a DC path to ground and the element without a DC path to
ground, anything that will bleed off that charge will cure
the problem. An RF choke works. A 4:1 voltage balun works.
A resistor works.

Perhaps we can convince a desert ham to hang an o'scope
on a clear-sky, dry-air system on a windy day and report
back here with some results. Many other hams have reported
the same thing during a dry-air snow storm.
--
73, Cecil http://www.qsl.net/w5dxp