[TowerTalk] Vertical dipoles

[John Tait]

K4SAV wrote:
> EI7BA wrote: Yes I am I am talking dipoles here..The dipoles have 
> single wire
> capacity hats at either end, which is the most efficient way of loading
> them.  The bottom capacity hat wire is 10ft over ground, and the top hat
> is at 55ft.  all the details are at
> http://www.iol.ie/~bravo/low_band_antennae.htm#My%20TX%20Antennae
>
>
> The antenna you are describing on that page is commonly called a top 
> loaded T, with two elevated radials (not a vertical dipole), although 
> the radials described are only 1/8 wavelength each.
Jerry OM... It is NOT a loaded T.. I do know what a top loaded T is, as 
I have built a few.. This is a dipole..
Rudy built it.... I have built  it.... others have built it....It works...
Talk to Rudy about your model, as I'm not an expert, though I do use eznec.
It does not use radials. What you call radials are the capacity hats. I 
could use coils, or linear loading, but capacity hats are more efficient
>   There must be some mistake on that diagram because when I put those 
> dimensions into EZNEC I get a resonant frequency of 2.43 MHz.  I don't 
> get any of the other characteristics described on that page either.  
> The antenna was described as having a feedpoint impedance of 65 ohms 
> and a 2:1 SWR of 170 KHz, and a gain of -0.25 dB.  I get a feedpoint 
> impedance at 1.85 MHz of 10.4 -j278 over average ground.  Bandwidth at 
> that frequency has no meaning.
> I tried to find the error.  I can make the antenna resonate on 1.87 
> MHz by lengthening the two radials to 133 ft each, but the feedpoint 
> impedance goes to approximately 12 ohms over average ground.  It's 
> even less over salt water.  I could make the two top wires 130 ft each 
> (instead of 65 ft each) and make the antenna resonate on 1.835 MHz, 
> but the feedpoint impedance goes to approximately 17 ohms over average 
> ground.  I could simulated a feedline that is not decoupled from the 
> antenna and causes a lot of ground loss and that would raise the 
> impedance and widen the bandwidth.  The gain is largely dependent on 
> whether you are talking about average ground or salt water.  So does 
> that diagram accurately reflect what you built?
>
>   
I think you're looking at the 80m antenna, not the 160m version. The cap 
hats on the 80m are 66ft tip to tip, and the 160m hats are around 130ft 
.    Please read Rudy N6LF's QEX articles on the links provided.. Please 
also read Tom W8JI's and LB Cebik W4RNL's comments on my page.
  I did not design this antenna... I built it from Rudy N6LF's design.   
I make this perfectly clear on my webpage.
190 countries worked on 160m  in five years says it works.

   73
        John EI7BA
>   Jerry, K4SAV