Hi Dave,
>A point was made that the shack earth should not be part of
>the aerial, this
> seems commendable common sense, however in a typical
> situation (like mine) I
> have an HF transceiver which has it mains safety ground
> carried via the
> chassis to the ground of the aerial socket, the outer of
> the coax carries
> this ground to my "RF" ground at the feedpoint of the
> aerial.
If it does, than something is wrong with the antenna to
feedline transition, the feedline, or the feedline to
station transition, or the equipment itself.
There should be no power mains connection to the chassis,
even on the neutral wire. In the USA, if we run a 120V
transformer or blower in an amplifier or anything else,
there should be no path to the chassis or the safety grounds
for that blower or 120 transformer primary.
In the USA, we are NOT allowed to isolate the station ground
from the mains entrance ground for very good safety reasons.
Any isolation transformer would be illegal unless the safety
ground crosses that point. Even the neutral did not cross
the poorest way to isolate noise or unwanted RF would be an
isolation transformer.
Audiophooles come up with some very strange ways to do
things. I don't know for certain, but I would not be
suprised if the isolation transformer idea came from an
audiophool web site.
All that aside I see quite a few homebrew RF amps with
transformers, blowers, and other things making a chassis
connection. Only the power line safety ground should
connection there. The shack ground is required by our
national electrical code to be tied to the mains entrance
ground for safety reasons.
> Inevitably some of the RF current generated in my
> unbalanced aerial will
> pass into the mains wiring...
> equally the converse will happen...
Choke balun or current balun.
> A weakness in my existing layout is of course that if I
> get a live to earth
> short anywhere in my property some of that fault current
> will pass via the
> ground of my HF transceiver to my RF ground. I have a
> current balun
> arrangement which should help effectively isolate the two
> earths at RF to
> some unknown extent but it will have negligible impedance
> at 50hz.
Why would it?
> If I ignore boring wiring regs I could arguably rely on my
> RF ground as a
> safety ground for the ham gear, however I am sure the
> delta connected
> capacitors in the mains input to the radio mains power
> supply will carry RF
> noise to the chassis....
A chassis does not need to be part of a radiating system,
especially since cures are so easy.
RF grounds that cause major changes in any station with
two-conductor feeders, ether balanced or coax, are a patch
for other problems.
If there is a separate earthing system, it should only be
for the antenna. It should not be for the station gear.
73 Tom
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