[TowerTalk] Antenna Resonance: ratio to height AGL

[Frank Norton KB8XU]

Hello TT'ians,

A request for help concerning assembly and adjustment of Cushcraft 40 meter 
Rotatable Dipole:

I found one of the older model Cushcraft 40M Rotatable Dipoles that Tom, 
N4KG mentioned to me in a prior email.  I can't locate specific 
instructions for this antenna. (the cushcraft tech site lists the manual 
but when u download it, it is the manual for the multiband dipole with all 
the traps--not much help.)

So anyway here r the details:  I have it at 12 feet or so off the 
ground--best I can do for testing.  I got the following SWR curve after 
carefully adjusting length from the center insulator to the trap and the 
trap to the tip.  Here are the SWR numbers I get:  6.975=1.91, [I know it's 
out of the band but I had to know ;-).] 
7.025=1.45,  7.100=1.45,  7.150=1.81,  7.200=  2.39,  7.250=3.00, 
7.299=3.66.  So  all this appears to tell me is that at 12 feet above 
ground the dipole has best SWR/resonance at about 7.050.

I know that as we raise it in height the resonant frequency should go up. I 
don't recall the equation; seems it was 25 kHz for ? feet increase AGL But 
will it resonate in the area of 7.100-7.150 where I need it to?  It will 
ultimately rest at 60 feet above ground--but once it's up, that's it I 
can't work on it.  (I wud have to hire someone again, or impose once again 
on the family lives of my friends.)

Isn't there some  way to figure this ahead of time?  As stated above, I 
think  there is a ratio of feet or wavelengths above ground to the kHz the 
antenna will go up in resonance.  But my MS plays tricks on my memory.  Can 
anyone help me out?  Anyone recall the equation/ratio, if it even exists?

I've checked the ARRL Antenna Book 19th Edition but cud not locate the ratio

Tnx in advance,

Frank, KB8XU


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