Service manual

168 8
Theory of Operation
TRANSDUCER THEORY
A3 Hp Amp.
The A3 Hp amp. senses the voltage across the DUT (Edut), and transmit the voltage (Edut)
to the vector ratio detector. The voltage across the range resistor(Err) from the A4 Lc amp.
is transmitted to the vector ratio detector through the A3 Hp amp.
The A3 Hp amp. also switches these two voltages to transmit to the vector ratio detector.
A4 Lc Amp.
The A4 Lc amp. senses the voltage across the range resistor (Err), and transmits the voltage
to the A3 Hc amp. The A4 Lc amp receives the feedback signal from the A6 vector
generator to cancel the current through the DUT. The feedback signal goes through the
range resistor.
A5 IV Converter & Lp Amp.
The A5 IV converter & Lp amp detects the unbalanced current “iD”, and converts the “iD”
signal into an equal phase IF signal. The IF signal is supplied to the A6 vector generator.
A6 Vector Generator
The A6 vector generator converts the IF signal from the A5 into two DC voltages,
proportional to it orthogonal (quadrature, 90 degree phase difference) vector components
by the phase detector. The two DC voltages are amplified by integrators and applied to
mixers, and are converted to a 240MHz signal which is in phase with the unbalance current
by mixing with the 240 MHz from the A7. The 240MHz signal is applied to the next mixer,
and is converted to a frequency equal to the unbalanced current frequency by mixing with
the 240 MHz + fm from the A7. The frequency signal is applied to the A4.