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.

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.

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.

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.

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.

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.


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!

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

and upward.

73's
Richard Clark, KB7QHC