Vic:
Because there is so much going on in EMI, and so much of that, being
extremely sensitive to boundary conditions, is unique to a specific
situation, there will always be room for respectful disagreement as to how
to solve or prevent problems.
If radiation from the exterior surface of the antenna feedline were the
only mechanism that causes emi, then you would be right, choking it off
would solve the emi problem. The energy in the transmission line would be
radiated by the antenna or turned into heat by either the line losses or by
the losses in the materials used to make up the choke. However, emi can be
caused by many other mechanisms, and as one other poster to the reflector
has reported, improving his RF ground substantially mitigated his problem.
I do agree that an effective RF ground is hideously difficult to achieve at
HF. I did not recommend using an 8 foot rod as an RF ground. I merely
observed that it is better than nothing. I admit that an 8 foot ground rod
with a short lead would be a quarter-wavelength, and thus would look like a
perfect open circuit at 10 meters. On the other hand, for typical soil, at
80 meters it would present a complex impedance on the order of 15 + J 25
Ohms. That is uncomfortably high, but far better than nothing.
The "least bad" HF electrode that I reported in my previous post was based
on an Army/Air Force study about 20 years ago. Whether or not it is worth
the considerable trouble needed to install it is a judgment call. I did
install such a system, and if I had it to do again, I definitely would. I
have had no emi problems at my station, despite the fact that my QTH is
bristling with all sorts of new-fangled "smart house" electronics.
73,
Steve
AA4AK
Brunswick ME
At 08:33 AM 1/29/2005 -0800, you wrote:
Stephen W. Kercel wrote:
Third, having no RF ground is a big nono. The problem is that the RF that
is on the chassis of your rig has to go somewhere.
I'm sorry, I have to respectfully disagree. If you have a balanced
antenna system, or even an unbalanced system with RF properly choked off
from the outside of your coax, there will be no RF on the chassis that 'as
to go somewhere'.
In addition, it is very difficult to provide an RF ground at HF. Even the
8-foot wire you mention will have significant impedance. And a ground rod
is of absolutely NO use for RF grounding, although correctly applied
ground rods may be useful for lightning protection.
--
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco
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