Antenna tuning

[Bill Hider]

Victor A. Dubois wrote:
> 
> I bow to the antenna specialists on this reflector and pose the following
> question.
> 
> I know the resonant frequency will change on the antenna when installed on
> top of a tower versus being at 6 feet or so. The question, how much acn I
> expect the resonant frequency of a 6 element 15 meter monobander to change
> when installed on a 120 foot tower versus at 6 feet? There are no other
> antennas on the tower to interactr with the beam.
> 
> Thanks in advance.
> 73,
> 
> Vic   N4TO
> n4to@ct.net
> 
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There are many ways to determine this:

1.  Model it on your PC using a variety of programs sold in QST.

2.  If you have the antenna built, raise it with a non-conducting rope,
pointing it straight up, with the reflector about 4 feet (or more) off
the ground and measure it with a handheld analyzer (AEA or MFJ are two
that seem to work adequately for this purpose).  A QST article in the
past year or so showed that this method is very, very accurate.

3.  My experience is that some antennas move up in freq 5%, others move
up 10% or more in freq as they are raised from a few feet off the ground
to their resting height a significant fraction of a wavelength in the
air, depending on antenna design.

I'd suggest (1) or (2) depending on whether it's vaporwear or hardware!

73!

Bill, n3rr@erols.com

--
FAQ on WWW:               http://www.contesting.com/towertalkfaq.html
Submissions:              towertalk@contesting.com
Administrative requests:  towertalk-REQUEST@contesting.com
Problems:                 K7LXC@contesting.com
Sponsored by Akorn Access, Inc & KM9P