[TowerTalk] Log Periodics

[i4jmy@iol.it]

> "Since nobody can actually know the performance of their antenna, it
> has to be that antennas are 95% mental and 5% metal."
> 
> 73 de Brian/K3KO

In case of horizontal polarized antenna, and expecially when the 
antenna gain is moderate, the ground reflections at specific angles are 
dominant to consistently reduce composite gain (even a total 
cancellation may occurr) or to put an extra 6 dB gain. 
In this case the comparison between antenna gain and individual results 
may lead to wrong statements because all what happened depends by 
peculiar and local factors.
An LP antenna has a gain that mostly depends by size (lenght) and 
number of elements of the active cell.
The active cell, when antenna elements are few and boom is short, is 
generally composed by 2 or 3 dipoles properly phased but closely spaced 
and stated a band, the rest of the antenna out of the active cell is 
practically uninfluent.
In other words, hardly a small LP can show a better gain than a 
properly designed 2 elements yagi and such LP gain is 2 or 3 dB less 
than a 3 elements yagi.
On the other hand, a long LP can have consistent gain but still it's 
like to have different monobanders along the boom, each one using only 
a part of it.
In terms of pure gain/boomlenght, an LP that covers a wide spectrum is 
a quite poor performer compared with a monobander where active elements 
are along the entire boom.

73,
Mauri I4JMY



> > Dinsterdog@aol.com writes:
> > 
> > > I have a Tennadyne T6 log periodic.  In 1999's CQWWSSB, I placed 
third in
> > the
> > >
> > >  zero district, SOABHP, mostly due to the number of Q's I worked 
on 10, 15
> > > and
> > >  20 meters with the T6. The guys who beat me have about 10 times 
the
> > aluminum
> > >
> > >  up vs my log periodic........so I think the T-6 showed it is a 
solid
> > antenna
> > >
> > >  considering it's on a 13 foot boom a top a 55 foot tower- Theres 
a lot of
> > >  good antennas out there- but the log periodic seems to have a 
crowd of
> > >  disbelievers- But for the money, the spaced used, and the over-
all
> > >  performance, along with the number of bands one gets with a 
single
> > feedline-
> > >  it is a good antenna choice for contesting, considering the 
expense and
> > >  resources needed for running monobanders.
> > 
> >     FYI the mult station (or second station) at W6GO is an LP. He 
says that
> > the reason he likes it is because it's got a bigger forward pattern 
than a
> > monobander or even a tribander which is useful in contesting where 
a real
> > sharp antenna can be a disadvantage.
> > 
> > Cheers,    Steve    K7LXC
> > Tower Tech
> > Champion Radio Products



--
FAQ on WWW:               http://www.contesting.com/FAQ/towertalk
Submissions:              towertalk@contesting.com
Administrative requests:  towertalk-REQUEST@contesting.com
Problems:                 owner-towertalk@contesting.com