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The S meter is calibrated in S-units from
1
to 9, and in
decibels above S9 to +90 db.
Readings on the S-meter will be
correct only when the RF GAIN control is at maximum sensitivity
(fully clockwise).
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3.2.4
NOISE SWITCH
(
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The noise pushbutton switch (located below the S-meter) ac
tivates a noise generator which permits the Receiver to be peaked
at the preselector for optimum reception.
No signal other than
the noise signal is necessary for this adjustment.
After the MHz
preselector is set to the approximate frequency desired, the noise
pushbutton should be depressed and held while the MHz control is
adjusted for maximum reading on the S-meter.
NOTE
If care is not taken, the preselector
may be peaked at an image frequency.
To avoid this condition, make sure that
the MHz preselector control is set to
the desired frequency.
The noise generator signal may be used for emergency align-
ment of the Receiver when no other signal source is available.
In
addition, the noise generator provides a test for Receiver operation,
since failures (including local oscillator failure) will result in
no noise output when the pushbutton is depressed.
3.2.5
RF GAIN CONTROL
The RF GAIN control varies the gain of the mixer and IF
amplifier stages by setting a fixed threshold in the AGC circuits.
Maximum gain is obtained with the control rotated fully clockwise.
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3.2.6
CRYSTAL SELECTOR SWITCH
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1
The CRYSTAL selector switch is a seven-position switch that
permits the operator to choose the exact frequency of operation.
Associated with the numbered positions of this switch are corres
pondingly numbered crystal sockets and trim capacitors.
To change
frequency, the operator first inserts the proper crystal into any
empty socket.
Second, the operator must tune in the signal and
adjust the crystal trim capacitor (located directly above the
crystal socket) for a maximum reading on the S-meter.
(See para
graph
3.3.)
The R position of this switch enables the Receiver to
accept the input from an external synthesizer.
\
3.2.7
CRYSTAL
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The local oscillator crystal frequency is determined by the
mode of operation and the band selected.
Table
3-2
and Figure 3-l
3-4
