[TowerTalk] Log Periodics

[Joe Reisert]

Brian,

Chuck, K1KW built two large (18 elements each on a 62 foot boom) 14-30 MHz 
LPDAs. He has them stacked at about 50 and 100 feet and can feed them in or 
out of phase. He has a potent signal indeed. I believe Chuck claims 8.5-9 
dBd free space gain for each antenna (not including ground reflections etc.).

73,

Joe, W1JR


At 01:28 PM 12/7/00 +0000, alsopb wrote:
>I would say that both of these posts are in the realm of speculation.
>
>There is no calculation for horizontal antennas I have done in
>EZNEC/AO that shows much modification of the vertical pattern due to
>antenna design with a few notable exceptions.  The exceptions are
>extremely long "boom length" antennas.  By long, I mean 5 wavelengths
>or more.  It may be possible to build such a LDPA so that at its
>highest frequency the boom is this long.  However, the design's I've
>seen for LPDA'S all have booms comparable to commercial yagi's.
>
>If you guys would provide an LPDA model for EZNEC, I'd be glad to run
>it and end the speculation.
>
>73 de Brian/K3KO
>
>
>
>Peter Forbes wrote:
> >
> > K7GCO writes:
> >
> > > Cheers,    Steve    K7LXC >>  This is very true but there is another
> > >variable.  IF THE HORIZONTAL PATTERN IS WIDER, SO IS THE VERTICAL 
> PATTERN and
> > >this fills the higher angles with far more RF than the loss of gain and at
> > >certain times of the day do a bang up job on DX also.  This is 
> comparible to
> > >a 2 element quad at say 1/2 wave or slightly higher do so well.  It's the
> > >lack of gain that makes it work closer to the ground.  High gain beams 
> don't
> > >work well close to the ground.  k7gco
> > >
> >
> > Is it NECESSARILY SO that a wide horizontal pattern means a wide vertical
> > pattern as well?
> >
> > The vertical pattern for a horizontal log periodic array is a function of
> > several things:
> >
> > (1) ground reflection effects
> > (2) ground impedance effects (when within one wavelength height above 
> ground)
> > (3) the spacing of the elements within the log cell which are active at 
> that
> > frequency (in other words the Design parameter of the array (tau) and the
> > relative element spacing constant (sigma)).
> >
> > In all my literature searches on the log periodic (both amateur and
> > professional) there is little discussion of the effect on the vertical
> > pattern when near the ground, with most computer modelling being free space
> > situations.
> >
> > Cheers
> >
> > Peter   VK3QI  ( an 18-29 mhz log periodic user)
> >
> > S IT NECESSARILY SO THAT A WIDE HORIZONTAL PATTERN
> >
> > >                          "Now you have the rest of the story."
> > >
> > >--
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> > >
> >
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