David,
Most any indoor antenna is in close proximity to the transceiver, and it
is quite likely (even with the most carefully balanced antennas) to have
RF floating around most everywhere, including the transceiver chassis
and any earthing wires.
I would suggest that you may be better off trying to create an RF ground
condition at the antenna side of the tuner and not worry about the rest
of the antenna system.
An RF ground condition can be created (actually forced) by attaching 1/4
(or odd multiple) wavelength wires to the ground terminal of the tuner.
The far end of the wire should be insulated because even with QRP power
levels, a high RF voltage can appear at the far end. If the quaterwave
wire does not create an RF Ground having an impedance of 20 ohms or less
at the shack end, then it is not an electrical quarterwave - antenna and
transmission line principles prevail.
Yes these 'counterpoise' wires may radiate as part of the antenna system
and cause pattern distortion, but with an indoor antenna, the main
concern is usually that a signal is radiated - most situations where an
indoor antenna is necessary, the amateur cannot be 'antenna pattern picky'.
73,
Don W3FPR
David Woolley wrote:
The requirement that I'm trying to meet is that the K2 chassis not be
RF hot and that, if I connect the mains ground, there is no
significant RF in that ground. RF choking the ground has the same
problem that the choke impedance will not be large compared with an
off resonant antenna. That requires driving an antenna that is, at
least approximately, balanced - in reality it's not possible for me to
get true balance, because the antenna has to be indoors.
A choked earth doesn't remove the need for something to carry the
return current, and whilst it may get called an artificial earth, it
is really part of a semi-balanced antenna, and unless it is massive
compared with the "antenna", will probably be more balanced that
unbalanced.
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