On Mon, 4 Dec 2006 14:47:34 +0000, Ian White GM3SEK
wrote:

....
When you're using an auto-tuner, your whole approach to antennas gets
turned around. Just put up whatever you want, or whatever you can, and
in most cases the tuner will take care of it.
....

The autotuner at the feedpoint is certainly an interesting solution to
convenient frequency agile operation.

The risk, as some have identified, whilst a match is obtained for the
transmitter, and transmission line losses are low, that antenna
performance (efficiency) may be lacking. You just can't tell by
looking at the VSWR meter on the radio.

I put some notes together exploring models of an antenna system based
on NEC models of the radiator, estimates of ground system loss,
calculated loss of a practical L match, and calculated transmission
line losses. There are three articles that may be of interest (John
and others):

http://www.vk1od.net/NaroomaEFW/NaroomaEFW.htm

http://www.vk1od.net/InvertedL/InvertedL.htm

http://www.vk1od.net/multibandunload...ical/index.htm

Some have mentioned avoiding high impedance resonances as they will
damage the tuner. Some of the articles above predict the voltage
impressed on the tuner, and for longish wires, it isn't nearly as
severe as using one of these tuners on 2.4m long mobile whip (as
people do, and in compliance with the tuner user manual).

Taking a system view, all three of the articles show that there is a
lower frequency limit to efficient operation of the antenna system,
and the major contibutions to loss.

Ground loss is commonly the most signigicant element for minimal
installations.

It seems obvious that in order to reduce ground loss, one should
improve the ground system. Taking that system perspective, one of the
ways (and it may be the best way in most situations) to reduce ground
loss is to lengthen the radiator.

Owen
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