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October 13th 06, 06:58 AM posted to rec.radio.amateur.antenna

Richard Clark Richard Clark is offline

Richard Clark is offline

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First recorded activity by RadioBanter: Jul 2006

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dipole length vs db

On Thu, 12 Oct 2006 23:30:17 -0400, (Fred McKenzie)
wrote:

Someone mentioned that you could reduce losses in the tuner by adding
external loading coils. It seems to me that you would just be moving the
loss out of the tuner into the loading coils.

Hi Fred,

The advice is good, and the logic demands you consider what you say.
What is being exported is the inductance and if you are good at it,
you can build a loading coil that exhibits less loss than the
inductance internal to the tuner.

This reduced loss comes about by larger wire, larger form factor, more
spacing between turns:
Larger wire has more surface area which is significant for skin
effect.
A larger form factor will allow more inductance to replace what is in
the tuner (it will not be a 1:1 even trade, however).
More spacing between wires takes us back to skin effect. Wires that
are in proximity closer than 3 diameters will force currents beneath
the surface of the wires (magnifying the skin effect's loss through
reduced volume for current).

Another virtue is that loading away from the tuner, up in the
structure of the radiator, allows a higher current to flow in that
structure. The general advice is to put the load at least 1/2 up to
2/3rds away from the feedpoint. Outside of this region has
diminishing results. THIS is where you will find gain over a bare
wire and for very short wires, that gain CAN be an order of magnitude.

73's
Richard Clark, KB7QHC

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