In a message dated 99-08-18 21:41:17 EDT, georgemain@worldnet.att.net writes:
> I am in the process of installing up on my tower an A4S beam from
> Cushcraft.
> I did all the assembly at the ground level, and I tune it (adjust the
> elements), for center of the bands, as Cushcraft instructions indicate.
> To verify the accuracy of the resonance curve, I pointed it vertical,
> with the reflector being the closest element to the ground (abt 4 feet),
and
> took some readings, on all 3 bands, with an AEA antenna analyzer.
>
> The result is that the resonance curve is shifted up (like for SSB
> tuning), on all bands!!
Generally Cushcraft dimensions work just fine.
>
> My question is, if this is a normal effect generated by the proximity
of
> the ground, and once in the air resonance will shift down, or I should trim
> it for CW portion to get a final CENTER of the bands result????
>
Yes, it's normal. Attempting to determine actual antenna resonance on
or near the ground is almost always useless because of the added capacity of
the ground which shifts the resonance up in frequency. Even standing the
antenna on the reflector may or may not be helpful. You really won't know
until you get it up in the air. If your tower doesn't have any guywires, just
hoist it up 30 feet or so and then take your readings. I use a tram line to
install antennas and can run the antenna partially up the tram to take a
reading. Then it can be lowered easily and any adjustments made with
re-testing done easily too.
Don't change anything until you see what it does in the air.
Cheers, Steve K7LXC
Tower Tech
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