(2) The input transformer to the tuned carrier amplifier is tuned to
resonance at 5 kHz during calibration.
The signal is then fed to a two-stage
transistor amplifier. The SENSITIVITY switch controls the gain of these stages (Q6
and Q7). A variable inductance and series capacitor in the emitter circuit of Q8
serve to exclude all frequencies from the remaining stages except the desired 5
kHz. The variable inductance L1 is tuned for maximum output during calibration of
the instrument. R36 is provided to adjust the gain of the tuned carrier amplifier
and is set during calibration of the instrument to provide 5 kHz level to the
synchronous demodulator.
(3) The primary components of the synchronous demodulator are transformer
T4, transistors Q4 and Q5, and diodes CR4 through CR7. The 5.0 kHz synchronizing
signal to the demodulator is fed from the push-pull oscillator and frequency
doubler through C5. The 5.0 kHz signal to be demodulated is fed through C19 from
the tuned carrier amplifier.
Increasing the level of the signal from the tuned
carrier amplifier results in higher synchronous demodulator output appearing across
the diode bridge and meter.
It is characteristic of the synchronous demodulator
that phase reversals in signal input, with no change in the synchronizing signal,
cause reversals in the output of the demodulator.
o. Battery check circuits (fig 2-11) have been provided to enable the
operator to determine the adequacy of each of the battery supplies.
Placing the
POWER switch in the REFERENCE BATTERY CHECK position connects the PERCENT INPUT
meter in series with the reference battery and resistors R457 and R462. Resistor
R458 has been provided to load the battery so that the battery check is
accomplished under load. R462 has been calibrated so that the lower limit of the
battery check band on the PERCENT INPUT meter coincides with 1.0 volts from the
reference battery BT105.
(1) With the POWER switch in the GALV BATTERY CHECK position, the PERCENT
INPUT meter is connected in series with the galvanometer battery supply and
resistors R461 and R455. Resistor R461 is adjusted so that the meter will indicate
at the lower extreme of the battery check band when 11.5 volts is supplied across
the load resistor R456. Since the measurement is made under load, it assures that
(2) With the POWER switch in the SEARCH BATTERY CHECK position, the PERCENT
INPUT meter is connected in series with the search battery supply and resistors
R453 and R460.
Resistor R460 is adjusted so that the meter will indicate at the
lower extreme of the battery check band when 11.5 volts is supplied across the load
resistor R454.
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