Topband: Top band Resonat freq of 90' tower

[George (K8GG) & Marijke Guerin]

Jake, K9WN wrote:

----- Original Message ----- 
From: <jacobsen_5 at msn.com>
To: "Charles Bibb" <zedkay at bellsouth.net>; "Topband" 
<Topband at contesting.com>
Sent: Sunday, August 26, 2007 7:29 PM
Subject: Re: Topband: Top band Resonat freq of 90' tower


> Charles, K5ZK, was wondering about the res. freq of his tower, 90' with 
> KT34XA. After giving him a wise guy and SWAG reply, my curiosity was 
> tickled, so I booted up EZNEC.
>
> Charles,  I used a 90' tower, 12" in diam, with a 32'/3" boom at the top. 
> ELNEC says resonant freq is 2.15 mhz.  Bandwith is about 200 khz +/-. 
> This might give you a starting point.   FWIW, the 90' tower alone is 
> resonant at about 2.6 mhz with abt 350 khz BW.........
>
> Again, good luck with the project.
>
> 73
> K9WN  Jake

I believe the coupling of the feed line to the driven elements of the 
KT-34XA probably lowers the resonant frequency by adding a little top 
loading.  I cannot prove it and Jake is correct that the 32 ft boom top 
loads the tower down to 2.15 MHz.

Connecting the center of the 3rd director and the center of the reflector to 
the antenna boom provides a lot more top loading bringing the tower and beam 
configuration to about the bottom end of 160.

73,        George    K8GG