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[TowerTalk] Re: Tuning Yagis - aimed upward, etc.

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Subject: [TowerTalk] Re: Tuning Yagis - aimed upward, etc.
From: (
Date: Thu, 8 May 1997 18:08:17 -0700

Aiming the antenna upward does work in some cases. Have had mixed success. 
The best is to have the low element (i.e. reflector) several feet above the 
ground. A friend of mine has a tuning method for LPDA's wherein this method 
is used; however, the #1 element was specified at being 1/4 wavelength above 
ground. A source element could also be placed behind the #1 element to tune 
for maximum F/B on the array.

Placing a Yagi antenna a few feet above ground (or rooftop) is certainly not 
a good idea, except to maybe check the coax. The coupling to mother earth is 
way too much. If there are any favorable readings, they will probably be 
coincidental at best. These comments are for full size elements only.

If a 20 mtr Yagi can be placed about 12', the elements can be checked and 
they will most likely be close; however, the feedpoint impedance will still 
change as it is raised to its final position. Most all antenna handbooks 
will have a chart in the fluctuations of feedpoint impedance of a dipole as 
a function of height above ground. Have had quite a lot of success in tuning 
linear loaded 40 mtr elements at 15'. Linear loaded 80 mtr elements like to 
be about 25'.

One way to do tuning at lower heights is to raise the low band element to 
its final height and note the frequency. Lower it to a convenient working 
height and note it again. Adjustments made at the lower height will track 
fairly well to the final height. The one caveat is to be sure the antenna is 
in exactly the same low location every time it is checked. Changes of a foot 
(even a few inches in a sensitive environment) can make significant changes. 
Of course, the higher the better, especially in regards to matching the 

Have a good day and 73,
                        Tom, N6BT
                        Force 12 Antennas and Systems
                        (Home Page )

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