Nulls are not caused by "angle of elevation" of the yagi boom. For all
practical purposes their angle is fixed by the frequency and height of
the antenna.
They are caused by the cancellation of waves when the direct path to a
given takeoff angle, and the ground "bounce" path to that angle differ
by an odd multiple of a half wavelength.
At HF with typical heights and boom lengths, elevation of a boom does
little to change a null. It will not change the angle of the null, but
might make a small change in the depth of the null. However, you would
pay for it in the gain in the lower (best) lobe. Primary lobe gain is
maximum with the boom parallel to the ground.
73, Guy
----- Original Message -----
From: "Michael Watts" <wy6k@yahoo.com>
To: <towertalk@contesting.com>
Sent: Saturday, February 02, 2002 12:03 AM
Subject: [TowerTalk] Super high antennas on 10 to 20
So has anyone tried using an elevation rotor on a high yagi? Why
couldn't
you have the best of all worlds with a high yagi and point it up for
high
arrival angles?
Michael WY6K
--- "Guy Olinger, K2AV" <k2av@contesting.com> wrote:
>
> I suspect that this is not so much a matter of where the main
> radiation pattern is, as where the nulls are in respect to the
> incoming angles.
>
> Very high antennas have better gain at the lower angles in marginal
> conditions, and those extra db's at the horizon are worth a lot. But
> the high antennas have deep nulls at common arrival angles. It would
> be easy and common to have the arrival angle on a minus 25 db null
in
> the high antenna's pattern.
>
> This would be the exact phenomenon accounting for being "stomped" by
a
> tribander. A 25 db null advantage to the tribander would be really
> hard to beat.
>
> Aside from getting some gain at very low angles, that's the main
> performing reason for stacks -- avoid pattern nulls on angle of
> arrival.
>
> 73
>
> ----- Original Message -----
> From: "David L. Thompson" <thompson@mindspring.com>
> To: <towertalk@contesting.com>
> Sent: Friday, February 01, 2002 5:21 PM
> Subject: [TowerTalk] Super high antennas on 10 to 20
>
>
>
> N4KG and W4ZV are right. The real high antennas can be at a
> disadvantage
> after the bands open. I had a 7 el 10 meter beam at 70 feet in 1970
> for the
> CQ WPX SSB and I had a great signal into Northern and Eastern Europe
> and the
> Far East but needed to lower the antenna
> to 40 to 50 feet when I got stepped on by a local with a 3el
> tri-bander at
> 50 feet in G or HP (then KZ5 Canal Zone).
>
> N4RJ tried all sorts of combinations and his final 10 meter set up
was
> 35/65/90 and about the same proportion on 15 and 20. The 35 foot
> antenna
> was often left on South America.
>
> Spend time on the lower antennas and only add antennas at 180 to 200
> feet
> when its the last option.
>
> 73 Dave K4JRB
>
>
>
>
______________________________________________________________________
> __
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>
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>
______________________________________________________________________
__
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The
> same place that pays for the hosting of this list: The eHam Store.
> Order online at http://store.eham.net.
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Order online at http://store.eham.net.
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