Ouch!! Here's some nit picking:
If the feeders are truly balanced, and narrow spaced for the frequency
> in use, such as window line 450 ohm nominal and 300 ohm nominal at HF
> bands, there should be minimal field outside the feeders due to the
> equal and opposite currents principle.
What is 'truly balanced'? The only way you get the phase in open
wire feeders exactly 180 degrees out of phase is by making absolutely sure
the physical length of each side of your dipole are identical. Feeders are
NOT 'truly balanced', but if you apply common sense, your antenna system can
be balanced.
>
> A well designed rig, installed properly, will not have RF in the
> shack. This means use of a well balanced tuner, and earthing measures
> that avoid having the distance to earth as a quarter wave of the band
> in use or odd multiples. This is where many have trouble, especially
> with unbalanced antennas.
'RF in the shack' has absolutely nothing to do with a 'well designed
rig, installed properly'!! If the length of one side of your dipole plus the
total length of your feedline is an odd multiple of quarter wave lengths,
you will have high voltages (commonly referred to as 'RF in the shack') at
your operating position. If you happen to hang an end (or both ends) of your
dipole wire directly over the top of your house, chances are great that you
will also suffer with the 'RF in the shack', simple because of the very high
voltage fields always produced at the ends of dipole wires.
>
> Use of true balanced antennas minimizes problems of RF in the shack,
> from both coax and balanced feeders. (The coax feed using a balun at
> antenna.)
True. And a true balanced ham antenna is a dipole with exactly equal
physical length for each side of the dipole AND a loop (such as a quad)
antenna.
>
> That being said, if a particular rig has sensitive digital logic,
> modern EMC methods of beads and choke cores on cables, improved bypassing,
> twisting power supply conductors and shielding them, all will help
> remove the RFI effects.
In my totally humble opinion, all of the above is tried AFTER you
make sure your antenna is not inducing a high voltage field into your room.
>
> Many hams persist in using off balance, off center fed antennas
> without balancing and thus will more easily introduce RF into the
> shack.
>
> Another method little known by hams, to mitigate RF in the shack
> involves running the coax feeder through a conduit, (the waveguide
> beyond cutoff type of filter). This affords certain off center fed
verticals little to
> no RF on the coax outer shield. It is a method easily implemented for
> a single problem band, although ferrite cable chokes may be easier to
> implement for multiple problems.
Hmmmm, a 80 meter waveguide...should be an interesting thing to
construct.
73,
> Stuart K5KVH
Tom/W4BQF
Omni 6 Upgrade/Titan amp
SOB#2
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