rf - Free and Open Source Software

52 Ohm 1 KW
SWR Meter
-Simple
-Inexpensive
-Effective
$15. 20
.o=::i _
RF
Field
Strength
Meter
1·400 mHz
REDLINE - BOX 431
JAFFREY, N.H. 03452
o SWR Meter $15.20 p.p.
o RF F.S Met er $8.60 p.p.
ORDER BLANK
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Comes with 5-section antenna and earphone
for modulation checking. Invaluable for tuning
any transmitter. Magnetic base for mobile
use.
only
Model FL·30 $8.60
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As we just saw, any possible physical
antenna must be made up of several different
atoms and so cannot be a perfect
isotropic antenna - but even if we could get
one, nobody would want it. rf power is too
difficult to generate to waste by beaming as
much signal straight up into space and
straight back down into the ground as we
send in the desired directions!
A ny practical antenna performs at least
some concentration of its signal, then, by
putting it all into its radiation pattern. What
we're really concerned with here is how we
can concentrate the signal even more. It
would be nice, for instance, to be able to put
all our power in just the direction we wanted
to transmit, without wasting any of it in
undesired directions.
Such antenna designs exist, of course, and
are known by the general name of "beam
antennas" since their purpose is to concentrate
as much of their power as possible into
a single beam.
At least four major types of beam
antennas have been developed, and many
different designs within each type bear
individual names. The types are (I) driven
arrays, (2) parasitic arrays, (3) reflective
systems, and (4) travelling-wave antennas.
Driven arrays include broadside arrays,
endfire arrays, and combinations of the two.
The Lazy H, ZL Special, 8J K beam, and
Franlkin Collinear array are examples of
driven arrays, as are most directive Be·
station installations.
Almost all parasitic arrays are of the
endfire type; the most common such design
is the Yagi antenna
Reflective systems are used primarily in
the UHF and higher-frequency regions, and
include the "big dishes" and the corner
reflector.
Travelling-wave antennas include the
terminated V, the rhombic, and their variations;
these are most usually used only at
low frequencies where the other types of
beams are not practical. One type of travelling-wave
antenna in wide commercial use at
high frequencies is the helical beam.
Any single beam antenna installation may
mix or match these types. Especially popular
among VHF workers is a combination of
driven and parasitic arrays in which several
separate parasitic arrays are driven at the
same time to form a driven array of parasitic
arrays. Fig. 7 shows the idea. At UHF, a
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