Hello.

Respecting the difference between a Yagi and a beam -- that's easy:
there isn't any!  A Yagi *is* a beam! (grin)  Beams can be relatively
broadly tuned (low Q) or narrowly tuned (high Q), depending upon the
type of matching network used.  Usually the matching components -- one
type is the so-called "gamma match" -- are located on the beam assembly
itself, that is, at the point on the boom where the coax feeds the
driven element of the beam.  Beam elements are cut (or have traps in
them which do the same thing, electrically-speaking) to provide the
directionality and resonance expected of a beam at the frequency in
question.

Log periodic antennas also have directivity.  Their elements are cut at
lengths which allow them to be tuned over a very broad band of
frequencies.  It is for this reason that many antennas which used to be
used on foreign broadcast transmitters were log periodic.  However,
because their frequency range is so broad, their gain over that of a
simple dipole, while noticeable, is nowhere near as much as is that of a
beam with the same number of elements.  As with everything else in life,
you don't get something for nothing or, as Robert Heinlien put it once
in a SF novel:  "There ain't no such thing as a free lunch!"

HTH!

Mike Freeman <[log in to unmask]>
Amateur Radio: < K 7 U I J >
... Go Mariners!
----- Original Message -----
From: "Michael" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Saturday, April 27, 2002 10:13 AM
Subject: Log Periodics, yagis and beams


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> Can someone point out the differences between those types of antenna =
> systems I have indicated in the subject line?  As well, which is the =
> favorite choice by most hams?=20
> Thanks:=20
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