The classic three winding voltage baluns force balance, but that can be
upset by the antenna not being quite balanced. The choke baluns allow
floating without forced ground reference that often gives better results.
On 8/9/2010 1:29 PM, Stuart Rohre wrote:
> Thanks, Jerry,
> "forced balance" was a poor description.
>
> What I should have said is the late W5YR found that with his simple
> ferrite cable chokes he was able to use ladder line, (parallel) line
> with his Tee tuners and had no further hot chassis issues. Now, he was
> using dipole type antennas, and he lived in an area that has much higher
> ground conductivity than some areas. His antennas were in the clear,
> which can affect RF on the shield, if one cannot keep the antenna at
> right angles to the feedline.
Feedline at right angles to the dipole is a way to not need a choke, but
that's not often achieved. Then the feed line couples more to one side
of the dipole and that induces unbalanced feed line currents without chokes.
Individual results can depend on many
> issues, and I did not address the issue someone else later raised of the
> elevated ham shack well above an earthing point. Most of those also
> need a ground tuner box, or quarter wave counterpoise wires for the band
> in use, to mitigate RF on the chassis.
In the elevated hamshack one needs to get everything bonded well with
short wide straps, and that bonding should include the desk and chair or
a shielding cage around the operating position, then earth ground isn't
so important except for lightning protection. That quarter wave
counterpoise wire can keep the RF voltages low on the equipment even far
from earth.
>
> His beads were larger than the types on the original bead chokes made
> commercially. They were of a diameter to enable teflon versions of 1/4
> inch coax slipped into them, and had about 3 X the length vs. their
> outside diameter.
> From several vendors there is more of a choice in pierced ferrite
> materials today, than in the first days of cable choke use.
And with the need for similar materials for RFI proofing computers, they
are more easily bought. Many materials have been available, but only in
truckload lots which made them impractical in hamshack needs.
>
> Stuart
> K5KVH
>
73, Jerry, K0CQ
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