Hi,
I have and the stacking distance depends upon the characteristis of
the LPDA. High taper factor (above .92 or so) and high spacing factor
(above 0.05 or so) require larger spacing due to the higher gain of these
arrays. For my system, Taper = .94 and spacing of 0.085, optimum
spacing models out at about 1.1 wavelength. Interestingly, the stacking
gain drops very slowly either side of this spacing. I used 55 ft since the
top antena is at 110 feet. This provides best angle fill and provides
a very good range of vertical take off angles with a top-bottom-in phase
-out of phase switch. The 55 ft spacing yields less than 0.2 dB
compromise on 20M (too close) and 0.3 db on 10M (too wide). On 10M
the patterns starts to show secondary lobes in the vertical plane but these
lobes are more than 12 dB down still. For shorter boom LPDAs I suspect
that the spacing will be smaller and I know of a pair of Tennadyne T-10's
that have been stacked with 30 foot spacing and perform quite well. With
LPDAs, you do not need to worry about the detuning effects of stacking.
73,
Chuck...K1KW
-----Original Message-----
From: jljarvis [SMTP:jljarvis@abs.adelphia.net]
Sent: Monday, March 18, 2002 11:59 PM
To: towertalk@contesting.com
Subject: [Towertalk] LPDA stacking distance?
OK, now I'm really curious. Who has stacked LPDA's, and
what stacking distance did you choose? Why?
N2EA
Jim Jarvis
Essex Vermont
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