There are? (were) some tilted / stacked LPDA 's at the
Collins Radio communication centers that I recall seeing
when I worked for them in the late 1960's in Cedar Rapids, IA.
IMHO, sloping booms is a self defeating strategy, at least
for SINGLE boom installations.
If tilted UP, the incident angle radiation is enhanced slightly,
but the GROUND REFLECTION radiation is lowered by a
greater amount (Imagine rotating the free space pattern
upwards ...or downwards).
I guess modeling is the only way to be sure for stacked LPDA's.
Tom N4KG
On Tue, 19 Mar 2002 17:12:07 -0500 "jljarvis" <jljarvis@abs.adelphia.net>
writes:
>
> Folks,
>
> I've lost track of who suggested this...but I would like
> to hear from anyone who has modelled or actually installed
> two log periodic arrays, stacked, but NOT parallel.
>
> That is, by tilting the leading edge downward, on the UPPER
> lpda, and the leading edge of the LOWER lpda UPWARD, it should be
> possible with an 18' boom lpda to have the first 10m elements
> spaced by 16', and the last 20m elements spaced by 32'.
>
> I haven't bothered to finesse the geometry, but it would appear
> possible to space and tilt such that you obtain maximum gain
> from the stack, when driven in phase.
>
> Anyone actually DONE this? W1CX relates seeing a pair of KLM
> 7-30 lpda's like this in Panama, while transiting the canal.
> For purposes of discussion, assume there will be no mechanical
> mounting issues.
>
>
> Jim Jarvis, N2EA
>
>
>
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