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Richard Clark · October 12th 06, 08:17 PM posted to rec.radio.amateur.antenna

On Thu, 12 Oct 2006 14:42:39 -0400, (Fred McKenzie)
wrote:

In article , ml wrote:

Currently i have a centerfed horiz dipole up pretty high

it's total length is less than 40ft, center feed via my sgc

i was thinking it'd be nice to have a SIGNIFICANT /real order of
magnatude type improvement in 'performance' or gain

ML-

I have a similar question, but I'm not looking for a "real" order of
magnitude improvement. I just want to get on the air.

Hi Fred,

Good, simple antennas are not going to show an "order of magnitude"
improvement under any circumstance short of issues related to loss.

If I only have room for a short dipole, say 40 feet, and use a tuner such
as the SGC or Icom AH-4, what is the penalty in DB for the lower bands
(160, 75, 60, 40) compared to a half wave on each band?

What do the manufacturers say? OK, they probably guarantee nothing
other than a match (I am familiar with the local manufacturer's claim
of loading a wet string.)

The radiation resistance of a 40' dipole in the 160M band is 1 Ohm.
The contribution of loss resistance in proportion to this reveals
efficiency/loss. If anything in those boxes contributes as much as 1
Ohm, then you are down by 3dB before the signal hits the airways.

The only question is can that additional 1 Ohm contribution dissipate
the heat without self destruction? Think about it, 50W of heat inside
that box. The manufacturer would probably guess correctly that you
would never feel it, unless you are working RTTY.

An additional 1 Ohm attributable to the manufacturer's designs may be
an outlandish assertion. Again, consult their specifications.

73's
Richard Clark, KB7QHC

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