On 1 Dec 2005 23:38:42 -0800, "Brian Kelly" wrote:


wrote:
On 1 Dec 2005 08:23:30 -0800, "Brian Kelly" wrote:


. . . .

I've seen suggestions here and there about simply aiming a beam
vertically upward and doing all the tuning at ground level instead.
Which would save an awful lot of time and effort. If it works. Does
anybody around here have any experience with this method and if so how
succesful was it?

Thanks,

Brian w3rv

It will get you close.

. . . Good. Beats having to taking the beam down and putting it back up
several times just to get in the ballpark. I expect to have to do a
couple of these final tweaking cycles after rough tuning at ground
level. Would be a *big* help.

However it really depends on the front to
back of the antenna. Dipoles do poorly this way, 2 element beams
slightly better. I've done 3 element 6m beams with the reflector only
4ft off the ground pointing up with excellent success. Seems the
breakpoint is some where around better than 10or 12 DB F/B ratio.

Per my response to W4ZCV hexagonal beams typically have 10-20 dB F/B
ratios so they're in range of your "breakpoint".

You do need distance from the ground or it acts like a reflector
and messes with your measurments.

Understood. Looks like you and W4ZCV are basically in agreement so I'll
follow you two in this direction.

Thanks!

The yabut/gotcha is until the beam is acting like one you don't have
the F/B ratio to rely on so it may take an iteration or two before you
converge. Once you are in the fine tuning range it should work
well pointing it up. This is a problem that most Yagis don't have
as tuning is limited to tweeking the match for the driver and maybe
the driven element length to make the match work right. So what
regular yagis are tuned up pointing up they are really just having the
match set up correctly(usually).

Allison