Richard Clark wrote:

Hello Richard ~ Nice to hear from you.

On 23 Oct 2006 17:41:37 -0700, "Brian Kelly" wrote:

I'm in the process of stringing two base-fed half wave verticals up in
a big beech tree, they're Dale Parfitt's End Fedz dipoles for 20 & 15M.
These antennas are described on this Web page:

http://www.universal-radio.com/catal...wire/4456.html

Hi Brian,

There are any number of curiosities about this link.
1. The antennas are marketed as half wave DIPOLES;
2. They have matching networks to 50 Ohms;
3. Some (if not all) have low power restrictions.

Why?

Why am I going to use them? Because they only cost fifty bucks apiece
delivered, I only have a barefoot 100W HF xcvr and I don't have to buy
or build two tuners before it gets too cold to mess with antennas.

A half wave dipole already comes close enough to match as to beg the
question: what more is necessary?

If I could install classic center-fed dipoles I would. But because of
the space-restricted installation geometry I'm dealing with I can't
pull the coax off at anywhere near a 90º angle to the vertical wire,
the coax would have to droop close to and parallel to the radiators
which would cause all sorts of problems.

Well, the best interpretation is they are not DIPOLES at all.

Well . . this is a semantics & definitions issue as an ME I'll leave
for you EEs to sort out. I'm just another hobbyist who calls any
conductive structure with it's first resonance at a half wavelemgth of
some specific frequency a "dipole" independent of where it's fed and
how it's oriented. Which of course lays me open to the prospect of
getting gored good by purists and others who have copies of the IEEE
dictionary. But that's OK, I have scars all over m'bod and have
survived nicely.

They are half wave monopoles which definitely demand matching.

Yes, they're two of Dale's "dipoles"installed as half wave monopoles.

But with
tinker toy sized components in that small box? Now we see why they
are power restricted (those components would be toast).

I don't have an amp and they're well known for being considerably
underrated as far as power handing is concerned.

The matching networks will be 12" - 18" inches above the the surface
and fed with 8X coax. The tops of eight foot ground rods will be
directly (+/-) below the matching network enclosures at the bases of
the verticals. I'd split open the jacket of the coax and solder
pigtails made from 3/8" flat braid to the coax shields just behind the
PL-259 fittings then tape/goop the joints to weatherproof them. The
other ends of the braid will be attached to the ground rods. There will
also be some "nominal" radials attached to the ground rods.

It sounds like it would be worth a try.

OK, good.

Will this arrangement eliminate the need for the usual types of 1:1
choke baluns by taking any I3 currents on the coax shields straight to
ground?

Skip it. Go straight path to ground, and make sure the coax hugs the
weeds all the way home. This will stabilize the match which is
notoriously wild if you have too much cable trailing around in the
open. Your concern for common mode is well founded.

That's what I'm looking for. I've been concerned about missing
something fundamental. Apparently I have not. Onward.

Now, let's return to the technical howler of calling these antennas
DIPOLES.

With all due respect Richard I've babbled on enough on that topic so
I'l leave it alone and let you work it out with Dale since he done it


This is marketing to the stupid, or by the stupid.

I wouldn't touch that comment with a ten foot pole!

http://www.eham.net/reviews/detail/3632

Buy your
own wire, and invest in quality components in a larger enclosure. This
will easily save half the cost and finding even a modest coil and cap
in the junk box will save you a trip to the post office (and the cost
of postage and handling). The worst you can do is equal the design.
(OK, so some could do much worse.)

I've built some number of tuners which could handle 2kW and then some
including one which used a 4" edge-wound roller inductor and a variable
cap with 1/4" plate spacing both remotely operated by giant Navy
surplus five-phase selsyns. Etc., etc., etc . . ad nauseam.

But right now all I want out of life is to get on 20 & 15 to snipe some
of the expeditions coming up this winter without having to fiddle with
the soldering iron. At some point after it warms up I'll do just what
you're suggesting, build robust tuners, use #10 wire for the radiator
and store the 100W "dipoles" for portable operations.

Still and all, the price is set at the disposable income level; buy
two so you have a spare when the first one blows.

I just might do that.

Thanks Richard.

73's
Richard Clark, KB7QHC

Brian w3rv