[TowerTalk] antenna tuning

[jim Jarvis]

Bob, AD5VJ wrote:  "...  one of the antennas I will be working on in  
the morning is going to be an 80 Meter dipole, but I can only get it  
up here at abt
30' then I will be taking it and putting it up at around 60 feet, so  
it sounds like I want to tune it high and expect the dip to
move lower in frequency at the 60 foot level (maybe a few Khz per 10'  
in height or so).

If I am understanding all the input correctly, the swr curve will be  
less affected by the ground effects and therefore seem longer
(more inductive) as I raise it higher above ground (lessening the  
capacitance).

-0-

Bob,

You definitely want to cut the 80m antenna LOW, and trim from there,  
not HIGH.

In my experience, antennas tend to move UP in frequency as they're  
elevated, at least
up to a half wavelength or so.

As a practical matter, local environmental effects will dominate the  
tuning of any lowband wire.
I always calculate 234/f, and add 5%, just to be safe.

Even more practical, it's easy to fold back the ends of an 80m or  
160m dipole, to move it up-band.
It's considerably more difficult to solder on wire to make it  
longer.     Note that you don't have to CUT
the antenna to move it up-freq.   Just fold it back and wrap it  
around itself.

Jim/N2EA