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

On Mon, 04 Dec 2006 06:49:11 GMT, Owen Duffy wrote:

On Sun, 03 Dec 2006 23:13:38 -0500, John Ferrell
wrote:

I am considering purchasing a remote auto tuner for my continuing
tinkering with verticals. My current focus is on 80-160 meters with
33+ foot verticals. The auto tuners specs claim a max inductance of
around 32 uh. The tuners computed with the ARRL program TLW20 require
much larger values of inductance.


Did you model the exact circuit of the SGC tuner? IIRC they use a
l/pi-l configuration and an autotransformer.

Will the Auto tuner (SGC-237) that claims to match any wire greater
than 28 feet long really do it?

The demands on the tuner will depend on how good a ground system you
build. If you use a poor ground system, a side benefit of the poor
efficiency is a subtantial amount of resistance in the feedpoint
impedance, though you are probably still looking at thousands of ohms
of capacitive reactance. If on the other hand you have an outstanding
ground system, the very low value of feedpoint R becomes challenging
for the tuner, and the efficiency you saved with the gound system
might be lost in the tuner.

Of course, the other option is to lengthen the vertical to raise the
radiation resistance so that it is not totally swamped by ground
system resistance.

Back to you question, will you get a match? If the tuner lives up to
its specification, you should... but you are looking at the world
through your VSWR meter, and that is a very limited view!

Owen
The SGC-237 is on order!
I appreciate the help in making my decision.
John Ferrell W8CCW

Nice tuner... Just remember John, no one can be too rich, too thin, or
have too many radials...

denny / k8do

On 5 Dec 2006 06:25:25 -0800, "Denny" wrote:

Nice tuner... Just remember John, no one can be too rich, too thin, or
have too many radials...

denny / k8do
I will never have any of those problems...!
John Ferrell W8CCW

On Mon, 04 Dec 2006 20:50:54 -0500, John Ferrell
wrote:

On Mon, 04 Dec 2006 06:49:11 GMT, Owen Duffy wrote:

On Sun, 03 Dec 2006 23:13:38 -0500, John Ferrell
wrote:

I am considering purchasing a remote auto tuner for my continuing
tinkering with verticals. My current focus is on 80-160 meters with
33+ foot verticals. The auto tuners specs claim a max inductance of
....
The SGC-237 is on order!
I appreciate the help in making my decision.

If you want to improve efficiency on 160m, think about raising the
radiation resistance and / or reducing the earth loss.

Possibilities to raise Rr include inductive loading high up, longer
radiator, capacity hat, more than one of the above.

Owen
--

On Mon, 04 Dec 2006 09:18:47 -0500, chuck wrote:

John Ferrell wrote:
I am considering purchasing a remote auto tuner for my continuing

As others have noted, the auto tuners will have no trouble matching a 33
foot vertical on either 80 or 160 meters, even over sea water.

Using one at the antenna may reduce losses in your coax since the swr
will always be low.

The auto tuners will introduce their own losses, as will any antenna
tuners, although with shorter antennas the losses may be greater. QST
had an article in which auto tuner losses and matching ranges were
measured and I think compared with conventional tuners. If I recall, the
results were less unfavorable toward auto tuners than I had expected.

To reduce auto tuner matching losses to insignificant levels, you might
consider adding some lumped inductance at the base of your vertical (or
even better, part way up as in center-loading). You can add a
capacitance hat as well. If you cause the 33 foot antenna to appear
resonant at either 80 or 160, you will see reduced auto tuner matching
losses on both bands. Just a rough approximation to the required number
of turns ought to work. You're only trying to provide enough external
loading to reduce the tuner's losses. Resonance really doesn't matter
much. If you do this, you should be able to enjoy the ease of QSY
without a serious loss penalty and without a need to switch taps or
retune manually.

Of course your 33 foot vertical resonant at 80 or 160 meters may not
perform well at 40 meters and above, or worse, may not provide an
impedance your tuner can handle at those frequencies.

Chuck, NT3G

I have updated the 28 foot vertical web page for those who may be
interested in my experience. I is at
http://www.dixienc.us/28FtVert/SGC237.htm

I am very pleased with the results using the tuner but it has only
been a few days, I am still in the "honey moon" phase. I outline the
considerations for me and a larger vertical at the web site.
John Ferrell W8CCW

John Ferrell wrote in
:

On Mon, 04 Dec 2006 09:18:47 -0500, chuck wrote:

John Ferrell wrote:
I am considering purchasing a remote auto tuner for my continuing

As others have noted, the auto tuners will have no trouble matching a
33 foot vertical on either 80 or 160 meters, even over sea water.

Using one at the antenna may reduce losses in your coax since the swr
will always be low.

The auto tuners will introduce their own losses, as will any antenna
tuners, although with shorter antennas the losses may be greater. QST
had an article in which auto tuner losses and matching ranges were
measured and I think compared with conventional tuners. If I recall,
the results were less unfavorable toward auto tuners than I had
expected.

To reduce auto tuner matching losses to insignificant levels, you
might consider adding some lumped inductance at the base of your
vertical (or even better, part way up as in center-loading). You can
add a capacitance hat as well. If you cause the 33 foot antenna to
appear resonant at either 80 or 160, you will see reduced auto tuner
matching losses on both bands. Just a rough approximation to the
required number of turns ought to work. You're only trying to provide
enough external loading to reduce the tuner's losses. Resonance really
doesn't matter much. If you do this, you should be able to enjoy the
ease of QSY without a serious loss penalty and without a need to
switch taps or retune manually.

Of course your 33 foot vertical resonant at 80 or 160 meters may not
perform well at 40 meters and above, or worse, may not provide an
impedance your tuner can handle at those frequencies.

Chuck, NT3G

I have updated the 28 foot vertical web page for those who may be
interested in my experience. I is at
http://www.dixienc.us/28FtVert/SGC237.htm

I am very pleased with the results using the tuner but it has only
been a few days, I am still in the "honey moon" phase. I outline the
considerations for me and a larger vertical at the web site.
John Ferrell W8CCW

John, re the lighting protection issue with the tuner.

I don't need or want to operate when there is a high risk of lightning,
so I disconnect the tuner. The last picture in this article shows how
the tuner is mounted and the simplicity of an effective isolating
switch. In the event of lightning strike, the inverted L wire will
probably side flash to the support mast where it is much closer. One
could of course build a sturdy arrestor near the tuner if you don't have
such an alternative.

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

Pleased it is all working well for you.

Owen

On Tue, 02 Jan 2007 02:07:57 GMT, Owen Duffy wrote:


I have updated the 28 foot vertical web page for those who may be
interested in my experience. I is at
http://www.dixienc.us/28FtVert/SGC237.htm

I am very pleased with the results using the tuner but it has only
been a few days, I am still in the "honey moon" phase. I outline the
considerations for me and a larger vertical at the web site.
John Ferrell W8CCW

John, re the lighting protection issue with the tuner.

I don't need or want to operate when there is a high risk of lightning,
so I disconnect the tuner. The last picture in this article shows how
the tuner is mounted and the simplicity of an effective isolating
switch. In the event of lightning strike, the inverted L wire will
probably side flash to the support mast where it is much closer. One
could of course build a sturdy arrestor near the tuner if you don't have
such an alternative.

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

Pleased it is all working well for you.

Owen


After reading your web pages I have begun to imitate your set up. I
will be using a 44 foot wire radiator. It will (is) angling down to
one of the ground rods. That will permit the tuner to be installed
inside the house. This set up is physically much simpler for me. The
tower is a crank-up/tilt over arrangement with no guys so the actual
rigging must allow for a lot of movement.

John Ferrell W8CCW