Heathkit DX-40 - Page 17

Needless
to
say,
no
attempt
has
been
made
here
to
cover
the
theory
of
antennas,
as
such,
since
much
has
been
written
on
this
subject.
The
possibilities
indifferent
antenna
types
and
different
feed
systems
are
many
and
the
factors
mentioned
herein
only
scratch
the
surface
of
the
subject.
Each
operator
will
need
to
do
his
own
investigation
into
the
advantages
and
disadvantages
of
the
various
systems
to
determine
just
which
one
will
best
suit
his
needs.
Basic
data
is
available
through
the
Radio
Amateur
Handbooks
and
other
technical
publications.
Some formulas that should prove helpful are listed as follows:
1 wave length in space = 300,000 meters
ke
Center
fed
dipole
one-half
wave
long
(length
in
feet)
=
468
mc
Folded
dipole
one-half
wave
long
(length
in
feet)
=
462
Fine
Zepp
antenna
one-half
wave
long
(length
in
feet)
=
492
mc
LOW
PASS
FILTERS:
The
harmonic
rejection
of
the
pi
network
output
circuit
of
the
DX-40
is
excellent
and
will
attenuate
harmonics
considerably
when
the
transmitter
is
properly
grounded
and
carefully
tuned.
However,
additional
harmonic
attenuation
may
be
had
with
the
use
of
a
low-
pass
filter
between
the
output
of
the
transmitter
and
the
feed
line
orantenna.
Such
a
filter
should
be
designed
to
handle
the
maximum
power
output
of
the
transmitter
and
must
be
operated
into
its
nominal
impedance.
An
instrument
to
determine
standing
wave
ratio
on
the
feed
line
is
a
necessity
in
every
ham
shack.
The
HEATHKIT®
Refletted
Power
Meter
serves
this
purpose,
and
may
be
left
perma-
nently
connected
in
the
feed
line
of
any
amateur
transmitter.
While
the
above
instrument
is
preferred,
the
HEATHKIT®
Power
Meter
will
indicate
maximum
power
output
when
tuning
the
transmitter.
It
will
not
indicate
standing
wave
ratio,
and
is
rec-
ommended
only
as
a
tuning
aid.
Additional information on antennas can be found in:
Radio Amateurs Handbook - ARRL
The Antenna Handbook ~ ARRL
The Radio Handbook ~- Editors and Engineers, Ltd.
The Antenna Manual - Editors and Engineers, Ltd.
The Beam Antenna Handbook - Radio Publications
Page 42