Cecil Moore wrote:
Brian Kelly wrote:
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.

Actually Brian, the IEEE Dictionary seems to agree with you.
It doesn't say a thing about the feedpoint position of dipoles.
Is an OCF a dipole? Is it a dipole if one of the poles is only
one inch long? The IEEE Dictionary seems to say that anything
that walks like a dipole, talks like a dipole, and radiates
like a dipole *is* a dipole, by definition. :-)

Heh. Somewhere along the line a long time ago some sage somewhere
stated that there are only two basic types of antennas, point radiators
which are really difficult to build and dipoles and their variants. The
concept stuck and I've been wearing it ever since.

73, Cecil http://www.w5dxp.com

Brian w3rv

wrote:
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.

I've used the duoband EF-20/40 (since replaced by the triband
EF-10/20/40) for several years for portable QRP operation. The real
advantage of these antennas for field operation is their light weight
plus simple erection by tossing them into a tree :

http://users.vnet.net/btippett/catal..._trail_qrp.htm

Dale W4OP is very knowledgeable and responsive. I would try a direct
e-mail to him via par at parelectronics.com , however his FAQ page on
the End-Fedz FAQ page states:

http://www.parelectronics.com/pdf/FAQ%20End%20Fedz.pdf

################################################## ################
Q: Do the EndFedz require a ground?

A: The simple answer is no. With over 4000 antennas in the field, we
know of one instance where RF was "in the shack." This occurred
with the antenna directly over the operating position. Moving the
antenna solved the problem. If you do ground the antenna at the
matchbox, you will likely see no change in VSWR or resonant frequency.
The only conditions where we were able to measure significant RF on the
outer coaxial shield occurred when:

1. The coaxial length was an odd multiple of ¼ wavelength AND
2. The rig was grounded.
In this instance we measured current -7dB down from the peak antenna
current.
Changing the coaxial feedline length OR removing the ground
significantly reduced the currents.
################################################## #################

Based on the above and my own experience (QRP rig plugged directly into
the coax connector), I doubt you will need a ground. As I said before,
ask Dale. He is extremely responsive and he seems to know what he is
doing (see below).

http://www.parelectronics.com/index.html

73, Bill W4ZV

Bill I think your post makes a number of points which need to be made
about the PAR "dipoles"and I for one have no further comments on it.

P.S. Since you want monobanders, you might consider rolling your own.
I made one for 40m but wanted the versatility of Par's duobander for
portable opertion. The designs below do require a counterpoise wire
but are quite easy to build. See multiple links at the bottom of this
page for more info:

http://www.aa5tb.com/efha.html

Outstanding article more HFers need to read. Thanks.

Brian w3rv

Richard Clark wrote:
On 24 Oct 2006 11:28:04 -0700, "Brian Kelly" wrote:

Why?

Why am I going to use them?

No. The "why?" was a rhetorical question about the three conditions
that were in conflict.

A halfwave dipole will match without need for extraneous components,
barring a choke which is for the consideration that brought you here.

Agreed.

Because they only cost fifty bucks apiece

Priced to sell. How anyone can have grief with this is a mystery, but
you cannot imagine the mail that came my way. I enjoyed the mail, by
the way; however, only Dear Abby posts mail for response and education
to the interested.

Fan mail is good for the soul. Enjoy.

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.

That is perfectly reasonable. If you have room for a halfwave end fed
wire, then you have room for the same sized sleeve dipole. Guess
what? It doesn't need matching as that comes free with the antenna.
It answers your problem about the 90° angle: the feed comes out the
sleeve to exactly the same point the TWO you are buying do.

OUCH! Oh Lordy, you're absolutely right Richard dammit . . and of all
people I should have immediately thought of a sleeve dipole for my
current HF applications because I built two of the things for 2M years
ago and they worked just dandy. For 2M all I did was grab some RG-58,
removed 19"of the jacket, rolled the exposed shield back 19", laid five
feet of nylon cord alongside the dielectric then sealed the whole
assembly with four feet+ of shrink tubing to seal the whole thing then
added a connector to the feed end and took 'em to the airwaves. I could
hang them anywhere via the nylon cord to get on 2M. Or I could roll
them up and stuff them into the glove compartment No tuning networks
required and the power handling capability was limited by the melting
point of the dieleleric or the jacket.

I can easily build similar antennas for the HF bands and maybe I will.
But not right now.

Write this blooper off to my raging Halfheimers . .

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.

Hams (amateurs) use the same distinction; I'm afraid you are only
going to see the argument among "professionals" notably those late to
the linear world.

Which is why I've excused myself from that one.

They are half wave monopoles which definitely demand matching.
Yes, they're two of Dale's "dipoles"installed as half wave monopoles.

Hmm, rhetorically, you've just slipped into the abyss. Four
quarterwave elements? And how are you going to feed them? Two
halfwave elements? Didn't you say you had space limitations? Of
course you did.

OK, OK . . jeez . . in my case they're half wave verticals, they're
single-band half wave monopoles, they're half wave vertical dipoles,
call 'em half-wave vertical washing machines for all I care about
splitting semantics hairs at this level all of 'em take up very little
horizontal space which is what's scarce here, instead they take up
"vertical space" which I have in abundance and will put to work

If you were on the air and described your grounded dipole with a
matching box, I guess you would have a lot of rag-chewing in line.

Get outta here with your "grounded dipole" bafflegab!

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.

I would have thought that might be part of the ad copy. I do note
that several are rated for less than 100W. I find that curious too
for a matching box that lends only .12dB loss.

That is about 1W of heat, not that I'm complaining, after all, a
Christmas tree bulb burns more heat than that and I would hardly call
that loss a limiting factor that demands derating from barefoot. A
copper coil can certainly tolerate that much heat - or just use bigger
wire.

OH! The capacitor will flash over? What are we talking about the
difference in a buck for a better cap? 5$? 10$?

Do we save $30 from NOT ordering the $50 backup, to simply change out
the under-rated cap for $20? Myself, I would pot the existing cap and
see what happens first (10 cents worth of epoxy).

That would change the tuning? OMIGOD!

Oy vey . . ! Calm down Richard and connect with reality willya?. The
End Fedz line is a collection of catalog easy-up antennas with
well-defined limitations offered for sale to those who can make use of
them for their specific interests and operating objectives. Is there
anything wrong with that? Of course not. Even at their worst they're
still not snake oil antennas like G5RVs which often cost fifty bucks or
thereabouts too.

I've been concerned about missing
something fundamental. Apparently I have not. Onward.

and upward.

Amen and g'night Richard, I enjoyed the educational joust.

73's
Richard Clark, KB7QHC

Brian w3rv

Brian Kelly wrote:
Heh. Somewhere along the line a long time ago some sage somewhere
stated that there are only two basic types of antennas, point radiators
which are really difficult to build and dipoles and their variants. The
concept stuck and I've been wearing it ever since.

There's got to be a history of the word dipole still in
existence. If you look at the Wikipedia definition of
"dipole", it refers to the equal and opposite charges
existing at two points, akin to the equal and opposite
charges existing at a point in time at the two ends of
a 1/2WL piece of wire. Your 1/2WL continuous piece of
conductor has two electromagnetic poles somewhat akin
to the earth having two magnetic poles. I suspect it was
ignorant hams who changed the meaning to two conductive
fishin' poles pointed in opposite directions and fed in
the middle. :-)
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote:
Brian Kelly wrote:
Heh. Somewhere along the line a long time ago some sage somewhere
stated that there are only two basic types of antennas, point radiators
which are really difficult to build and dipoles and their variants. The
concept stuck and I've been wearing it ever since.

There's got to be a history of the word dipole still in
existence. If you look at the Wikipedia definition of
"dipole", it refers to the equal and opposite charges
existing at two points, akin to the equal and opposite
charges existing at a point in time at the two ends of
a 1/2WL piece of wire. Your 1/2WL continuous piece of
conductor has two electromagnetic poles somewhat akin
to the earth having two magnetic poles. I suspect it was
ignorant hams who changed the meaning to two conductive
fishin' poles pointed in opposite directions and fed in
the middle. :-)

Indeed. We purloined the term then perverted it. Dipoles are
everywhere, water molecules, proteins, theyt're all over plasna phyics,
as you point out Mother Earth is a dipole, election campaigns . .
sigh.

73, Cecil http://www.w5dxp.com

Brian w3rv

Cecil Moore wrote:

Is the reflector on a single-band Yagi a dipole?

No, or yes, depending on semantics.

ac6xg