Tnx for the input on Penniger Aluminum. That's one of the problems we face
when trying to homebrew verticals or beams. Where to get the components?
Your point about insulating the base is valid, Rob. My commercial vertical
dipole has two monster insulators that hold it away from a piece of steel
about 3 or 4 ft. long. The idea was to mount this steel in concrete.
Instead, I bolted it to a strong 10 ft. aluminum pipe, thus raising the
bottom and the feedpoint quite a bit. I feel this helps the radiation
somewhat, but the main reason was to get the antenna off the ground and away
from kids and animals.
I've used this vertical dipole concept continuously since 1993, especially
on all of my contest expeditions. But for contests, I use a wire version.
The first few years I used 2x 5m sides, but later switched to 2x 6m sides.
For installation, I use a telescoping fiberglass rod, extended at the base
by wood (e.g., a 2x4 or similar). Originally I used the DK9SQ fibreglass
masts which were 10m long. They are available in the U.S. In the meantime
I've switched to using the masts which are used for the "Spiderbeam" and are
12m (40 ft.) long. These are heavier duty and even longer.
I don't know if the Spiderbeam products are available in the states yet, but
I know the guys personally for over 15 years. They are reliable. The cost
is about 80 EURO which is about $100, plus shipping.
For info, see: www.spiderbeam.de
I don't know if Spiderbeam (the company) sells the masts separately, but the
German Ten-Tec distributor, "Appello" sells them separately.
See www.appello-funk.de and go to Online Shop.
Appello also sells a 5-band commercial vertical dipole (made of aluminum,
not wire). This is a Swedish product and is of outstanding build quality.
My plan is to install this to replace my openwire-fed vertical. That way I
won't have to tune all the time. Of course I will need to build a mono-band
for 40m if I switch to this new 5-bnad vertical dipole.
Ground Proximity:
Earlier, Jerome brought a brilliant point concerning the effect of ground
when these vertical dipoles are mounted close to ground.
Not just in theory, but in practice there seems to be a little bit of
unbalance. However it is negligible. Now this is based on amateur testing,
not scientific testing.
I have two ladderline fed antennas, the horizontal dipole and the vertical
dipole, and for the longest time, my second high-power matchbox was an
unbalanced matchbox (T-Filter) with an external Radio Works Remote Balun.
With the T-Filter and running about 750w, I always had some RF in the shack,
but it was noticeably worse on the vertical than on the horizontal. If I
used the Annecke on the dipole, I had no problem at all with RF in the shack
on either of the two antennas.
For me it was good enough for government work. I simply bought another
Annecke (after several years searching). A purist would do the following:
Using two small lamps, 1 each clipped to each of the two sides of the
ladderline, adjust the antenna for resonance and then shorten slightly the
bottom half of the vertical dipole. This will solve the problem for one
band but I don't know how it will react on the other bands.
Finally, I only ever had problems with a bit of RF in the shack when using
the T-Filter and operating on 40m. I had no problems on the higher bands.
As I said earlier, the base of my Vertical Dipole is about 10 ft. off the
ground.
Bottom Line: If you can't swing a tower and a beam, nothing beats a
vertical dipole (for DX) and feeding it with openwire enables multiple bands
while keeping it simple. But you do need a good symmetrical matchbox (or a
Monster Balun like Bob builds with you standard tuner).
73
Rick
-----Original Message-----
From: tentec-bounces@contesting.com [mailto:tentec-bounces@contesting.com]
On Behalf Of Rob Atkinson, K5UJ
Sent: Sunday, July 10, 2005 3:49 PM
To: tentec@contesting.com
Subject: [TenTec] ladder line
I have thought about rigid vertical dipoles before but didn't do anything
because i was afraid ground effect would unbalance them (I didn't want to
deal with insulating the bottom of the bottom half also) unless they were
higher up than I wanted to go, and i knew the feedline would have to come
away at 90 degrees for some distance. If the feed point were 30 feet up or
more that might be kind of tricky (a lot depends on your site and what's in
the way). if i were going to try one, i'd probably think about a wire
dipole suspended from a rope between two structures if possible.
But, while we're on the subject, I'd like to put in a plug for an outfit
here in town that should be of interest to anyone who wants to work with
aluminum: these antennas we're discussing are pretty basic structures and
can be homebrewed (probably should be). I have a guy here in my town who
started a business about 2 years ago selling heavy gauge aluminum pipe and
machined mounts, clamps and split sections. Also portable antenna masts and
accessories, stainless and galv. nuts and bolts, cable, guys, coax and
connectors, 6061 Al tubing, custom machining, tiltover bases. He goes to
hamfests around here and ships. Was at Dayton but his business has been
pretty much word of mouth. Saw him this morning at the Aurora IL hamfest
and he told me he just shipped some of his product to Egypt. If he can ship
there he can ship to you and I've looked at his stuff and it all looks like
high quality:
Charles Penninger KC9DAO
Penninger Radio, 619 S. 9th Ave. St. Charles IL 60174,
phone/fax 630-584-7641,
http://www.penninger.com,
radio@penninger.com
rob/k5uj
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