wrote:

The autotuner should be fairly efficient on 40m and up, though you
might want to add a few feet to the vertical to avoid the high
impedance of a half wavelength on 20m, but I dunno.

Not a problem. When a half-wave vertical is fed against ground, the
impedance is lower than many people imagine, and well within the
efficient matching range of most auto-tuners.

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.

At the old QTH, I had a 33ft pole which was guyed at the top, and had an
auto-ATU and plenty of radials at the bottom. That simple pole worked
well on 3.5-18MHz, and would work after a fashion from 1.8 to 30MHz. In
addition, it could be tilted over quickly and various other add-ons
plugged into the top.

The simplest was a 12ft fishing-pole extension, which favored DX on
3.5-14MHz.

Another configuration added a 30ft horizontal extension wire to make an
inverted-L, about a half-wave on 40m and about a quarter-wave on 80m.
That one was excellent for 80m DX, and quite usable on 1.8MHz.

For more serious 1.8MHz work, the free end of the horizontal wire could
be very quickly lowered to ground level, and an extra 100ft of wire
added. This gave a quarter-wave on 1.8MHz, and also an end-fed half-wave
for 3.5MHz. It was good for local working on 3.5MHz because the
high-current portion was horizontal at about 30ft.

I really couldn't tell you what the exact height and wire lengths were -
whatever, the auto-tuner took care of it.


--
73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

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
--

On Mon, 04 Dec 2006 19:43:55 GMT, Owen Duffy wrote:

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


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
There is a lot to digest there... I am still at it
John Ferrell W8CCW