[TowerTalk] Dipole length vs diameter -- a theory question

[Larry B.]

Thanks TTers!

I want to thank all of the members who answered my theoretical question, 
either publicly or privately.  As it turns out, what I thought might be a 
"simple" question is actually rather deep.  In short, there is no simple 
solution.

The best answer came from Rick, N6RK, who forwarded a link to K6OIK's paper:
        https://www.fars.k6ya.org/docs/K6OIK-Dipole-Basics-ARRL-Pacificon-Oct_2019-r1.pdf
This gives more detail than I will probably ever be able to assimilate.

The most humorous (and still serious) was from Ed, AG6CX, who turns out to 
have been at MIT at the same time I was, although I don't think we ever met. 
(We can't agree if Harvard is up or down Mass Ave from MIT!)   I declined 
his three attachments.

I also downloaded the book:  “Radio Antenna Engineering” Edmond A. Laport, 
Chief Engineer RCA International Division VOA.  [ 
http:snulbug.mtview.ca.us/books/RadioAntennaEngineering/ ]  Thanks Ron, 
W8RJL.  Probably more practical stuff than I will even need as well!

73 -- Larry -- W1DYJ



-----Original Message----- 
From: Larry Banks via TowerTalk
Sent: Tuesday, January 28, 2020 13:19
To: Ham - Tower Talk
Subject: [TowerTalk] Dipole length vs diameter -- a theory question

Hi TTers,

A friend of mine asked me what first appeared to be a simple question. 
Paraphrasing:

          “How do I calculate the length of my HB 2M halo, based on
            the diameter of the aluminum rod.  Is it like propagation
            velocity with coax?”

My quick answer was: “No, propagation velocity only relates to transmission 
lines.  Use the graph in the literature for your design to start.  Modeling 
will help.  But let me do some research.”

I had realized that I really didn’t know the answer.  I have looked in my 
two usual places: the ARRL Antenna Book and Wikipedia and found lots of 
hand-waving and the usual references to the “K-factor” graph, which appears 
to be derived experimentally.  BUT NO THEORY, other than vague references to 
the capacitance and inductance of the rod changing with dimensional changes 
which, in fact, is similar to transmission lines.

Do any of you have a reference to some real theory and an equation that 
allows me to calculate this based on length, diameter, and material 
characteristics?  (Ignoring environment effects of course.  This would be 
for free space.)

73 -- Larry -- W1DYJ