On Sep 28, 9:29?am, Michael Coslo wrote:
wrote:
On Sep 27, 10:53?am, Michael Coslo wrote:

Why not,

[use a 1/4 wave dipole]

other than the fact that such a short dipole will present a
feedpoint impedance that has a low resistive part and a high reactive
part?

That's a pretty good reason, though. 1/4 wavelength dipoles - make sure
to read that as total antenna length, not 1/4 wavelength per leg, are
just a troublesome combination that a lot of tuners can't tune very well.

I'm not convinced. Depending on the transmission line impedance and
length, the shack-end Z could be within the matching range
of the Transmatch.

I don't consider the G5RV and OCF to be 'trick' antennas.
They're
simply intelligent combinations of dipole and feed systems that
have been worked out to present reasonable impedances so that
line losses and Transmatch requirements are reasonable.

They are very clever. The OCF especially is a joyful
playground to work
on with antenna design programs.
It is a great way to learn both the
programs and antenna theory.

Agreed. But so are other implementations such as trap dipoles and
the classic dipole-with-ladder-line feed, where you try different
dipole and transmission-line lengths.

Often the idea of "low SWR" is put out as if it is the sole criteria.

Too often.

In
defense of SWR lovers, modern Rigs really hate High SWR,
especially
reactance of the capacitive kind.

Well, that depends on how you define 'modern'...

But a 50 ohm resistor has 1.1:1 VSWR,
and some manufacturers have taken advantage
of that sort of thing in the past.

Not just in the past. Google "Maxx-comm matcher" (try different
spellings). Those folks are still in business.

The problem as I see it is that most new folks these
days start out with an "all band" radio, and are inclined to want a
antenna that is likewise all band.

Which may or may not be a good idea. If the only bands that
are open when you have time to operate are ones where your
antenna works poorly, the result is going to be frustration.

A lot of Western and Eastern EU, Great Britain, Iceland,
Norway, most of
South/Central America, about half of Africa, Israel, Australia,
Antarctica, and a couple others.

On which bands?

No JA or far eastern countries, but I
haven't tried really hard, I just work 'em if I happen to hear them.

Of course from EPA, VK-land is about the antipodes.

I once accidentally worked a fair part of a contest once on 75
meters on
probably around 3 watts, mostly into California - I had tuned the
antenna, and forgot to turn the power back up. I had works
around 25
QSO's before catching that one.

Situational awareness, that's all. With my rig, the power level is
pretty obvious.

Of course, that isn't quantified data, it's just anecdotal. But running
at QRP levels does make for a more stern test of an antenna's
abilities,
especially if there isn't obvious signs of it, such as not getting calls
answered. Sold me on the thing.

The Ultimate Test is "what have you worked on it?" Theory is great
but the real proof is in the QSOs.

The technical details are that it is a 96 foot total length dipole, up
around 55 feet, the center support is a short length of pvc tubing.

I suspect that the 96 foot length was decided because that's what
would fit in the available space.

The ladder line is soldered to the respective dipole wire. Ladder
line makes
an almost straight drop to the Shack window. Definitely not the
best
thing going, but not too bad.

Actually, what you describe is pretty close to optimum for a simple
multiband antenna system in limited space, which I suspect is the
main issue.

Are you using true ladder line, or "window line" (Twin Lead with
holes punched in the insulation)? True ladder line (heavy wire, wide
spacing, mostly air insulation) has lower loss and less weather
effects. If the line is short there's not much difference, but as
frequency and line length increaseit can be worth changing out.

Depending on the shack-end impedances, different Transmatches
can have more or less loss. The worst-case scenario is where
a 4:1 balun is used with a shack-end impedance that has low resistive
and high reactive values. The poor Transmatch has to
try to deal with one quarter of the resistive part!

73 de Jim, N2EY