[TowerTalk] KT34XA Pre-Raising Checkout?

[n4kg@juno.com]

Pointing the antenna straight is a valid method of checking SWR,
but it takes more than a couple of feet.  I recall seeing a 
short piece in QST? where the author computed the minimum
distance the reflector needed to be above ground vs. F/B ratio.

Bottom line, the lower the F/B ratio, the higher the reflector
needs to be raised above ground to minimize earth effects.
If I remember correctly, low F/B antennas need to be raised
to have the reflector 20 ft above ground (for 20M) and high
F/B antennas need to be raised to have the reflector 10 ft
above ground.

A rope tied up on your tower and pulled out can be used 
to raise the antenna vertically.  Attaching a pulley to the
sloping rope and using another rope through the pulley
allows you to raise and lower the antenna while standing
near the antenna.

de  Tom  N4KG


On Mon, 7 Aug 2000 Kurszewski Chad-WCK005 <Chad.Kurszewski@motorola.com>
writes:
> 
> > Are there any checks I can do (other than the obvious length 
> > measurements) to confirm that things are tuned for the desired 
> > band segments?
> > 
> > For example, if a MFJ-259 is connected while the antenna is 
> sitting 
> > 2-feet off the ground, will it show any resonances that can be 
> > interpreted? (I'm waiting for the balun, so can't check it 
> experimentally 
> > yet).
> > 
> > 
> Actually, a very effective method for any yagi with
> decent F/B is to point the antenna straight up, with
> the reflector on the ground.  If possible, raise the
> whole antenna so the reflector is a couple feet off
> the ground.  The key is straight up.  Then check the
> SWR.  It will be VERY close to the SWR when installed.
> Works great!!
> 
> Chad  WE9V

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