Vectronics VEC-131K - Manual (Page 32)

VEC-131K Owner's Manual Aircraft Receiver Kit
30
Diode D3 is a germanium detector, and serves two purposes. It “demodulates”
the IF signal into two components: an audio signal and a DC level that
corresponds to the strength of the incoming signal being monitored. Capacitor
C27 removes, or filters, any residual RF components following detection.
IC U3 is a dual-section operational amplifier using a LM358 device. The first
section, shown as U3A on the schematic, amplifies both the DC and recovered
audio from the detector. The audio from U3A is feed to the volume control,
R18. The audio amplifier is a LM386 IC (U4) and was designed for low-voltage
battery applications.
IC3B, the second section of the LM358 op-amp, is a DC amplifier. This stage
converts the detected DC component to a level compatible with the AGC input
of the MC1350 IF amplifier.
Specifications:
Tuning range ...................................118 to 136 MHz, typical
Sensitivity........................................better than 0.5 uV across tuning range
IF frequency ....................................10.7 MHz
Power requirement ..........................9-volt transistor battery, alkaline preferred.
PC Board dimensions ......................3.300" x 3.000"