[VHFcontesting] 6m Array Switching

[Mike Clarson]

David: Is the "ground gain" a real number? When doing non-ionizing radiation
calculations, (same thing, but usually in the transition zone between near
field and far field) one is supposed to figure in ground reflection, but one
never sees it when doing actual measurements.--Mike, WV2ZOW

-----Original Message-----
From: vhfcontesting-bounces at contesting.com
[mailto:vhfcontesting-bounces at contesting.com]On Behalf Of David A.
Pruett
Sent: Saturday, July 03, 2004 11:07 AM
To: Ev Tupis; VHFContesting eMail Remailer
Subject: Re: [VHFcontesting] 6m Array Switching


Ev,

It only takes a few minutes to construct a model of this antenna in K6STI's
AO program.

All antennas:   14.14 dBi @ 7 degrees
Upper pair:     12.67 dBi @ 6 degrees
Lower pair:     11.84 dBi @ 12 degrees

I'm sending you .PCX files of the radiation plots separately, since the
reflector strips off attachments.

Before anyone gets too excited about these gain numbers, keep in mind that
these include 6 dB of ground gain and the 2.1 dBi gain of a dipole.  If you
back these out of the values shown, the numbers make sense, particularly
for the "all antennas" array.  The "pair" numbers are a little higher than
might be expected, for two reasons.  First, with the pairs the computer
shows that the immediately adjacent (but unused) element has some amount of
current coupled into it, so helps somewhat.  Also, the coupling to the
other dipoles drops the radiation resistance of the driven elements
somewhat, causing more current to flow for a given power input (vs. a free
space reference dipole) thus more gain.

One interesting observation is that dipoles (with their donut H-place
pattern) create nice fat lobes in stacked arrays.  The lobes are a lot
fatter than when long boom yagis are used, which might not be a bad
tradeoff if you're aiming for higher angles.

Dave/K8CC


At 07:44 AM 7/2/04 -0400, Ev Tupis wrote:
>Hello everyone,
>I am assembling a 4-dipole multi-driven array (horizontal polarized,
>stacked up my tower).  At first, I was thinking about simply stacking them
>all 12' (5/8-wave) apart and feeding them with 3/4-wave 75-ohm harnesses
>and calling it quits.  However, my thoughts are now wandering and am
>interested in exploring the ability to select between:
>
>Upper Two (50' & 38')
>Lower Two (26' & 14')
>All Four  (50', 38', 26' & 14')
>
>with the desire to focus the elevation component of the array to take
>advantage of different DX conditions.  A couple of questions for those
>in-the-know...
>
>Has anyone done this (array switching on 6m) with any degree of success?
>  - How have you accomplished it?
>
>What height does one use to calculate the takeoff angle of each
combination?
>
>"Let the tread begin" :)
>
>Ev, W2EV
>