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.
Inevitably some of the RF current generated in my unbalanced aerial will
pass into the mains wiring...
equally the converse will happen...
G3JVCs approach to this seems eminently reasonable to me, albeit probably
expensive!
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.
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....
Since I have very little confidence in the low impedance of my RF ground
(the gardener dug up some of it) I cannot trust it as a safety ground at
the moment... however the more I think about it the more I am convinced that
G3JVCs solution is correct, to establish a good quality trusted "clean"
safety ground independent of the grid and to achieve galvanic isolation by
the use of an isolating transformer.
I am sure someone will suggest that I operate a link coupled balanced feed
doublet, however it is a small garden and I do like to use 160m!
Regards to all, David G0FVT
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|