determined by C2 and T1.
operation frequency of the instrument.
amplitude of the oscillator output. The output of the oscillator, appearing across
R10, peaks at 5 kHz rate and is used to drive the synchronous demodulator. The 2.5
kHz signal from the oscillator is fed to the magnetic modulator from windings on
a 5 kHz output. This 5 kHz output is proportional in level to the DC input of the
magnetic modulator and its phase is dependent on the direction of the input
current. R4 is the front panel zero adjust used to balance the modulator. The 5
kHz signal from the magnetic modulator is fed to transformer T3 which is the input
for the tuned carrier amplifier.