"Wayne" wrote in
:

I am using a whip antenna mounted on a metal patio cover. Results are
good on 10 and 12 meters, and contacts have been made down to 40
meters. (Matches were not obtained on 15 or 30 meters) The whip is 8.5
ft long (a longer whip is under consideration). It is fed through an
antenna tuner and about 25 feet of RG-58. I'm about to replace that
with RG-8.

Taking this to mean that the ATU is at the tx end of the 25' of RG58...

It is challenging with that topology get get good antenna system
efficiency when the monopole is less than about 17% of a wavelength.
Working that backwards, your 2.6m whip is 17% of a wavelenght on 15m
wavelength or 20MHz.

The contributions to poor efficiency are feed line loss under standing
waves, ATU loss, and if the whip is magnetic stainless, conductor losses
in the whip.

RG8 will have lower losses, but the result will be a more challenging
load for the ATU and its losses will increase, consuming some of the
benefit.

You really need to take a system perspective because there is a complex
interaction of the system components.


Any comments on how to hold down feedline losses. One suggestion is
to use two parallel lengths of RG-8 so that half the current runs
through each. Also, site geometry would allow open wire feed.

Paralelling two cables reduces Zo to one half, but the matched loss per
metre is the same. The loss under standing waves depends on the actual
load impedance which you probably don't know.


Possibilities?


A remote ATU, a longer monopole.

Owen