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Hi Dick...answers are as follows. Am not an antenna guru, just tried
something and it worked! 80 screams and 160 is just OK...really need
some beverages to make the system tick!
Dick Green wrote:
>
> Yes. I don't know much (hardly anything) about shunt feeding towers, so
> anything you can tell me will help.
Look at the ARRL hanbook for some ideas on how to make the linear
loading wires and matching devises.
>From your description, it sounds like
> the cages are only 26 feet long, is that right?
Ummm...lower section is 26'...attached at the 25' level and the 4"
level...then the cage tapers to a "point" where all 3 wires come
together at @ 9 - 12" off the ground then back up @ 2' to the enclosed
matching network. Top view looks like this...O's represent the tower X'
Represent the cage:
X-------X
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X
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O
O O
The dashed lines that represent the "T" are made from aluminum for the
top bond and the bottom is made from 1/2 and 5/8" plastic PVC. Both top
and bottom supports are fabricated like telescoping antenna elements
which can be adjusted for proper match then held fast with a compression
clamp, just like elements.
> Do you have to have the
> tower lowered to 40' for the matching network to work, or can you raise the
> tower all the way up and still adjust the network for a match?
Either way will work, however, if the height is changed then the
matching capacitor must be adjusted.
> What's the
> effect of tower height on effectiveness of the antenna for DX?
Actually, what you are striving for is a quarter wave on 160...which is
hard for the average guy to do. The top antennas are a capacity hat
which makes the antenna electrically longer than it physically is.
Believe the ARRL handbook has calculations for this.
>Is the
> network motorized and remote controlled?
Mine is manually controlled...have to go 250' out to the tower to adjust
it. The caps are just plain air variables...but vaccuums are better and
in the works here. 160 2:1 SWR bandwith is about 35 KHZ, 80 is around 80
KHZ. At this station its centered on 1828 KHZ and 3525 KHZ. So 160 is
perfect for me...80, is so so...so I compromise and fake the rig out on
3795 KHZ with a tuner at the radio. Ther appears to be little
degradation of Rx and Tx signals with a 5 or 6:1 SWR on 3795.
What do you have for radials?
Have just 8 80 meter long radials...with tons more planned. They do not
have to be all that long though. The antenna gurus can tell us that 120
are best!
>
> I'm mainly interested in 160, but 80 could be interesting, too. I'm using an
> inverted vee at 65' for that, so could probably get lots of improvement with
> a shunt feed.
>
> Could be a little tricky here, as the tower is a motorized U.S. Tower
> rotating tubular, remote controlled blind from the shack 250' away.
Not a problem with it being blind...just have it set up right and check
it often...cannot see mine either.
>Cranks
> down to 22', but lives at 50' most of the time. Goes up to 70' for contests.
> Somehow I'd have to figure out a way for a shunt feed to be compatible with
> raising and lowering the tower, as well as rotating it.
50' would be an ideal starting ground...a little ingenuity and
creativity would be needed to attach it to the tower, but, really thing
it can be done.
>Any suggestions?
Hope this is a start. Lemme know how it works out.
>
> 73, Dick, WC1M
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