I have seen two commercial antennas advertised that are each 43 feet tall,
and have no traps/stubs, etc.
There appears to be a 4:1 balun at the feedpoint. Mentioned, is the
requirement to have a tuner at the driving end of the feedline, and max
VSWRs in the 4:1 range.

Playing around a bit with EZNEC, the feedpoint impedances over the
operating range have some large swings. Can anyone shed light on how
effective the antenna should be?
Wayne
W5GIE

On Mon, 27 Jun 2011 18:21:50 -0700, "Wayne"
wrote:

I have seen two commercial antennas advertised that are each 43 feet tall,
and have no traps/stubs, etc.
There appears to be a 4:1 balun at the feedpoint. Mentioned, is the
requirement to have a tuner at the driving end of the feedline, and max
VSWRs in the 4:1 range.

Playing around a bit with EZNEC, the feedpoint impedances over the
operating range have some large swings. Can anyone shed light on how
effective the antenna should be?
Wayne
W5GIE

Hi Wayne,

Actually, it depends more on the ground, or its proximity. If you can
get all the energy into the antenna (hence the tuner and BalUn), then
it leaves (the whole point of our hobby). If you have very few
radials and you are close to ground, when that energy leaves, a lot of
it is absorbed into the ground (not very productive).

Now, the height of this radiator can be something of bad thing for the
higher bands. 10M will become deaf because most of the energy is
oriented high into the sky, and deep into the ground. True, you
"could" force a decent match, but that is only half the story of
antennas. The same is probably true for 11M, 12M, down to a fairly
good match and operational application for 20M and below to, maybe,
60M.

EZNEC should bear out instructive numbers and graphics to all these
observations.

One curiosity about this - the 4:1 BalUns. This sounds like a Hail
Mary throw - a sop for the sucker. Do you count yourself among that
select population? Why? Because technically they would be UnUns.
Further, it is strange to think that a transformation ratio of 4:1 is
applicable anywhere, much less everywhere.

73's
Richard Clark, KB7QHC

On 6/28/2011 11:02 AM, Richard Clark wrote:

One curiosity about this - the 4:1 BalUns.

As with many of these "matching devices at the base of a vertical"
they're not actually a broadband 4:1 ideal transformer. they tend to
have a fair amount of leakage inductance and capacitance, and (by
empiricism) they have a design which generally improves the match over a
wide band. At low frequencies, where the feedpoint Z is low, the
shunting effect of the interwinding C isn't as big, so it acts more like
a transformer. At higher frequencies where the feedpoint Z is higher,
the interwinding C tends to "bypass" the transformer, so it works less
like a transformer, and you see more of the Z of the antenna.

You can fool around with some test data and a lumped model (with lots of
parasitics) and come up with some numbers for the parasitics that works
out pretty well and combined with some loss in the feedline, makes the
typical match at the transmitter end not too bad (within the range of a
tuner that can handle, say, 2.5:1 or 3:1, mostly reactive)

It is almost impossible to *design* such a thing from that data. I am
quite certain that these things were designed by empiricism. Spreading
the windings or squishing them, choosing various winding ratios, etc.
until it works "good enough".


The underlying problem is, as you pointed out, that a 43 foot radiator
on higher bands has a pattern that is somewhat less than ideal.

A trapped vertical might be a better solution, although mechanically a
bit more complex and definitely more "antenna looking"..

On Tue, 28 Jun 2011 11:27:24 -0700, "Wayne"
wrote:

Thanks for the comments Richard. Indeed, the EZNEC model that I looked even
created a question of which direction was best for a 4:1 "balun". That
would require more examination of the data than I have yet done.

Hi Wayne,

The Hail Mary I spoke of also includes:
requirement to have a tuner at the driving end of the feedline
Kind of a belt and suspenders solution which in the long run makes
this purchase an expensive option to simply buying staged tubing. In
that respect, the only value added could be a decent mount....

My interest would be in a half sized version of the antenna (or less) for
20m and above.

Hmmm, sounds like you are a prospect for my suggestion of staged
tubing.

I have a pretty good ground available in the form of a metal
patio cover.

And I would presume this to mean an elevated vertical design - good.

The no-brainer approach is to use full sized 1/4 wave
radiators for various bands.

There's no obvious advantage there when you have to use a tuner
anyway. They would be helpful in taming the mismatch, so go ahead.

But a simple way of tuning a single radiator
for multiple bands is more appealing, since band changes are much simpler.

Look into the topic of "folded monopoles."

73's
Richard Clark, KB7QHC