Topband: THE ITINERANT 160 METER ANTENNA PROJECT

[Jim WA9YSD]

I ran comparisons side by side over the years with folded dipoles, bazookas against just a plain Jane wire dipole. You can believe what you read.
 
Stay on course, fight a good fight, and keep the faith. Jim K9TF/WA9YSD


________________________________
 From: Tom W8JI <w8ji at w8ji.com>
To: Jim WA9YSD <wa9ysd at yahoo.com>; Top Band <topband at contesting.com> 
Sent: Sunday, August 5, 2012 8:58 AM
Subject: Re: Topband: THE ITINERANT 160 METER ANTENNA PROJECT
 
<I had read in a Hand Book for the 1930's the 3 wire folded dipole and 2 wire folded dipole had a couple factor of 1. This would make this antenna the preferred driven element for a long yagi.>>>

Why? Unless we know what they meant by the use of the phrase "coupling factor", we can't possibly extrapolate the meaning to infer anything about coupling in a Yagi.

I have not seen the exact text, but most likely they mean coupling from one conductor to the next inside the dipiole is unity....which has nothing to do with how that group of conductors couples to anything else in the world. It would really only mean that group of conductors or wires behaves as one conductor or wire.

<<Folded dipoles are all so used when installations require long lengths of feed line.>>

Only because their impedance closely matches the impedance of low-loss open wire lines available years ago. This meant the open wire line operated with a low SWR on the band the dipole was cut for.

Other than feed impedance, they are just a dipole. They have the same radiation resistance as a regular dipole, using the IRE definition of radiation resistance.  The only changed is impedance seen by the feedline.

<<Back when the Bazooka or Double Bazooka or other wise now known as coaxial antenna back around 1970 I think when I saw it in Ham Radio Mag.. Its coupling factor was around 0.9>>

That antenna was entirely false in theory and concept. The article, as I recall, did not accurately describe how the antenna worked. That antenna is just a thick dipole with a stub across the feedpoint. The stub internal conductors and the coax jacket introduces a little loss, so it has LESS gain than a regular dipole.

I was aware of the antenna because a person who worked for me started raving about them, and selling them. His supposition, based on the article, was they had "gain" and had increased bandwidth, and less noise. The theory made no sense on paper, and when I compared one to a regular dipole the same material and thickness they were identical, as near as I could tell.

<<<No some had told me that later on the coupling fact was really Velocity Factor. Now how can the velocity factor gets interpreted as to how well a driven element couples when compared to gamma match elements or Dipole or a folded dipole or bazooka?>>

It doesn't. Don't believe everything you read.

One book we have, considered to be a bible on baluns, starts on the second page with a misconception of balance and the behavior of dipoles and coaxial lines, and a flawed test to prove the theory. The entire book is about balance, and the foundation shows a misunderstanding of the cause of common mode current. This why, later in the book, a balun that isn't even a balun is described.

This is a hobby without much peer review, and yet we expect people, articles, or books we hold in high esteem to be right 100% of the time. This doesn't mean they are worthless, just that we need to understand things are not flawless.

73 Tom