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.

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

John Ferrell W8CCW

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


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

I have a SGC-230 (the big one) and an approximate 35' telescoping
whip on the R/rear of a 30' 5th wheel and it tunes fine on the lower
bands, including 160M. I have to shorten the whip up a bit to get it
to tune on 10M though.

S.T.W.

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

I once forgot to attach my bugcatcher so my SG-230
tuned a single four foot bottom section and reported
finding a match on 75m. The question is not will it
find a match but will it put any power into the antenna
at that "match" point - or is the tuner itself just a
dummy load?
--
73, Cecil http://www.w5dxp.com

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

I once forgot to attach my bugcatcher so my SG-230
tuned a single four foot bottom section and reported
finding a match on 75m. The question is not will it
find a match but will it put any power into the antenna
at that "match" point - or is the tuner itself just a
dummy load?

That's precisely the point. If you wanted to match a 30ft whip on the
lower bands, and didn't have a tuner, you would be thinking about large
air-wound base loading coils.

The small inductors inside amateur auto-tuners are nothing like that
standard of construction, so the losses inside the tuner will be higher.
As Cecil says, when a tuner is forced into a tough situation, its 'load'
impedance may consist mostly of internal losses... and an auto-tuner is
perfectly capable of matching that.

One of my prized possessions is a Racal military auto-tuner that is
rated to handle 1kW continuously into a 30ft whip at 2MHz. Sure enough,
it contains some very large air-wound inductors, with the kind of high-Q
construction that you'd expect to see at the base of a mobile whip.

A really good amateur project would be to combine the smart controller
of a modern auto-ATU with your own individual collection of large
inductors, capacitors and relays. However, it would take some guts to
buy an auto-tuner, remove all the undersized RF components, measure
their inductances and capacitances, and then throw them away!


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

Ian White GM3SEK wrote:
A really good amateur project would be to combine the smart controller
of a modern auto-ATU with your own individual collection of large
inductors, capacitors and relays. However, it would take some guts to
buy an auto-tuner, remove all the undersized RF components, measure
their inductances and capacitances, and then throw them away!

And then install a foot long hi-Q air core coil where
once rested a toroidal coil. :-)
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote:
Ian White GM3SEK wrote:
A really good amateur project would be to combine the smart
controller of a modern auto-ATU with your own individual collection
of large inductors, capacitors and relays. However, it would take
some guts to buy an auto-tuner, remove all the undersized RF
components, measure their inductances and capacitances, and then
throw them away!

And then install a foot long hi-Q air core coil where
once rested a toroidal coil. :-)


Yes, that's the idea... well, roughly the idea...


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

A really good amateur project would be to combine the smart controller
of a modern auto-ATU with your own individual collection of large
inductors, capacitors and relays.

That really would be great. I'm keeping that in mind for some day.

For a non-random-wire installation and not too many bands, you can go
with manual switching of networks. When I lived in an apartment, I
had a magnet wire antenna that consisted of two random lengths fed in
the "middle." As such, every time the antenna broke and I put it back
up, I needed a new match on each band. This is the kind of a situation
where an autotuner really shines; I decided to use a remote manual
tuner instead:

http://www.n3ox.net/projects/servo

When I moved into a house, I was able to put up something a little
sturdier for the lower bands. Since it's always the same radiator
and always the same ground system, I'm just using switched L-networks
at the base to match it. It's 40 feet tall; the 80m matching network
is a 20 turn tapped coil, #10 copper wire, about 3.5 inches in
diameter. The other matching networks have air variable caps and 2"
self-supporting #10 coils.

http://www.n3ox.net/projects/lowbandvert

John, if you're thinking of using a 33 foot vertical on 160,80, and the
higher bands, might I suggest an approach where you use a GIANT tapped
coil matching scheme for 160m, taps switched with a big relay, and then
have relays to select whether you're using the 160m/80m matching
network or the autotuner. For both of these bands, an inductor with
the bottom end attached to the ground system with a tap near the bottom
for the feedline and a tap up further for the antenna should work fine.
It's basically an L-L step-up L network.

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.

It's really the bands where the vertical is significantly shorter than
a 1/4 wavelength where you need a high-Q matching network.

Dan

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 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
--