Bird Electronic 4314B, Operation Manual

Page: 19 / 48

Theory of Operation
7
less voltage gain. This is applied to meter M to indicate the peak
power in the line. A portion of the DC output of amplifiers Q2 and Q3
is fed back to resistor R4 and to amplifier Q1. Resistor R4 is matched
to resistor R5 to provide unity gain to the amplifier. This feedback cir-
cuit maintains the output from Q1 and U1 to keep capacitor C3
charged to that value which yields unity closed loop gain.
The capacitor continues to energize Q2 and Q3, to maintain the read-
ing of the meter even though the peak of the pulse is no longer applied
to the amplifier assembly input. Only the peak power is indicated even
though there is a wide fluctuation of input power.
Because of capacitor leakage, diode back resistance, and transistor
input current, there will be a decay in the circuit that limits the time
the amplifier system will retain its output level. As the circuit decays,
the meter will return to zero if no additional pulses are received at
resistor R5.
Figure 2 Schematic Diagram - Element
RF Coaxial Line
XMTR
or
LOAD
LOAD
or
XMTR
Directional Coupling
Diode
Detector Element
Meter
DC Contact
Circuit Board