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3.1.3. Modulator Balance
For low frequency analysis, i.e. if the centre frequency is lower than four
times the bandwidth selected, it is necessary to adjust the balance in the
first modulator in order to suppress the unwanted components from the
mixer. The procedure is as follows:
Set
The FREQUENCY SCALE selector to range required.
The MAIN SCALE POINTER should be at the left hand end of the
scale (as low a frequency as possible).
The INPUT selected may either be "Direct" or "Preamp.", but there
should be
no
connection to the selected input.
The "Selective" mode on the FREQUENCY RESPONSE push-
buttons should be selected, and the smaiJest bandwidth which
encompasses "0" Hz selected on the SELECTIVITY CONTROL.
Depress the "Analyzer" push-button and switch the READ OUT
SELECTOR to a "Lin" position. Then, turn the OUTPUT SECTION
ATTENUATOR switch anticlockwise, until a significant deflection is
obtained on the meter.
Turn the two modulator balance controls alternately until a minimum
deflection is obtained on the meter. It may be necessary to turn the OUT-
PUT SECTION ATTENUATOR switch progressively anticlockwise.
Note: The balance procedure is not affected by the position of the IN-
PUT SECTION ATTENUATOR switch.
3.1.4. Filter Sensitivity Adjustments
It is necessary to adjust the levels in the filters so that all the filters have
the same relative attenuation at the centre frequency. The procedure is as
follows:
Select "100 mV" position on the INPUT SECTION ATTENUATOR and
"x 1" on the OUTPUT SECTION ATTENUATOR. The GAIN CONTROL
knob should be in the calibration position.
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