3.8
Oscillator
Frequency
Calibration
The
RF
oscillator frequency can be calibrated
to
a high
degree
of
precision using
the
harmonics
of
the
internal crystal
oscillator
and
an external all-wave receiver. The
latter
is
utilized
as
a frequency transfer unit. I
(1) Set
the
mode
switch at XTAL.
(2) Insert
the
"standard
frequency" crystal, preferably at
a multiple
of
1MHz.
For
spot
frequency checking,
at
say
10.7MHz, use a 10.7MHz crystal.
(3)
Set
the
RF
slide switch
at
LOW.
Adjust
the
FINE
control
as
required.
(4)
Connect
the
RF
output
to
the receiver
input,
direct
or
through
a small coupling capacitor
to
the
rod
antenna.
(5) In
the
following example, use
of
a 1MHz crystal will be
given.
(6) Tune
the
receiver
to
5MHz,
or
5th
harmonic
of
IMHz.
Then by carefully tuning
both
the oscillator and receiver,
an audio
beat
will be heard. The oscillator
is
adjusted
to
zero
beat
and
the dial reading
is
noted.
At
other
frequen-
cies spaced 1MHz apart, the same procedure
is
repeated,
namely, oscillator setting
tuning the receiver retuning
oscillator and noting the reading on the dial.
Practical use
of
harmonics
up
to
the
tenth
or higher
is
possible. However, care must be exercised
in
selecting
the
proper harmonic, especially at high
RF
when a rela-
tively low frequency crystal
is
used.
NOTE: When a receiver equipped with a
beat
frequency
oscillator
is
used, the measurements can be sim-
plified. The
"zero-beat"
condition
is
at
the
point
where the steady
beat
is
heard
most
clearly.
8
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