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Old September 24th 06, 07:43 PM posted to rec.radio.amateur.antenna
[email protected] n3ox.dan@gmail.com is offline
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First recorded activity by RadioBanter: Jul 2006
Posts: 137
Default Multiband Vertcal Antenna?

"Cecil Moore"
If the vertical is much over 5/8WL long, its take-
off-angle is too high for proper operation. 5/8WL
~600/f = 21 feet on 10m. Your 40-45 foot height
would only be good up to about 14.3 MHz unless you
figure out a way to shorten the wire above that
frequency.


Cecil's absolutely right about this... but, a suggestion. Right now,
above 14MHz, the bands aren't so hot. 17m is open a lot, 15m is open
sometimes, 12&10 almost never.

I'm using your setup #2 on 80m, 40m, and 30m and have been quite happy
with it. The radial field is 27 radials ranging between about 20 feet
and 40 feet (out to the edges of my yard) I'm using one of the 12m
Spiderbeam poles. I built my own L-matching networks for the base,
just because I didn't have an autotuner. I've noted good DX
performance. I don't have any quantitative numbers, but I'd make my
recommendation on another basis.

I expect a good multiband vertical costs about the same as a 40 foot
telescoping fiberglass pole + decent autotuner. Radial costs are the
same...

However, the antenna *versatility* of the pole + autotuner is much
better. You get better parts for your money. You will certainly be
able to load up a 40 foot vertical on 17m and up for noncritical
communication.... when signals are s9, you won't notice that they're
not s9+ 10dB. If some really good DX comes on 17 and conditions are
marginal, go outside and drop the pole two or three sections and
reattach the wire to the tuner! Now you've got a 5/8ths vertical on
17m!

The pole will come in handy for portable and field use; the autotuner
can be used to match whatever you want to try out in the back yard, and
having a nonconductive fiberglass support is great for experimentation.

Something I thought about trying, and would if I actually had an
automatic tuner, is rigging up a short inverted vee doublet at the top
of my 40 foot pole. It would be short enough to be only bidirectional
on 20m and up. Also install a good radial field for the low bands.
Homemade open wire line runs from the doublet at the top down to the
ground. On 80, 40, and (maybe) 30m, feed both conductors of the
feedline against ground. On 20m and up, feed the doublet as a doublet
instead. You just need a couple of relays to perform the switching
tasks remotely. This is an old approach to a multiband wire antenna
with good performance on both the low and high bands. A nice pole and
automatic tuner just makes it all the easier.

In fact, if you want to save even more money, do the doublet/vertical
thing but build one of Cecil's all-open-wire matching networks for the
higher bands. Some relays and some ladder line, a pole that costs EUR
80, and a bunch of wire, and you've got a good antenna system.

http://www.qsl.net/w5dxp/notuner.htm

One further thing to recommend the 40 foot telescoping fiberglass pole
is that you can make it easily disappear when you want to. Mine stays
inside when I'm not operating on the lower bands. Of course, I'm just
using it as a vertical; it takes 1 minute to take it outside, clip on
the guys, and raise the vertical wire. It would be a little more
involved to put up and take down a doublet all the time.


73,
Dan