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
1
MHz 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.
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