Electro-Metrics EM-2115, Instruction Manual

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EM-2115 APPENDIX C FUNCTION AND DESCRIPTION
(EM2115C-5)
The output of the input switching circuits is applied to a variable gain wideband amplifier
circuit. A control voltage supplied by the Microprocessor Board (A1A3) sets the overall gain of
the amplifier.
The output of the amplifier circuit is applied to an IF attenuator with a total range of 30
dB. The attenuator is controlled by logic commands from the Microprocessor Board (A1A3).
The output of the attenuator circuit is applied to a buffer circuit that provides two outputs;
one to the IF Amplifier Module (A3), the other to the rear panel PRE IF Output Connector
(A13J10).
The output of the attenuator circuit is applied to a buffer circuit that provides two outputs;
one to the IF Amplifier Module (A3), the other to the rear panel PRE IF Output Connector
(A13J10).
The high voltage tuning circuit provides the 0 to 98 V tuning voltage required by the va-
ractors in the active tuning circuits on the RF Frequency Range Bands and the Stator Board As-
sembly (A2A16A1).
Using the 8 V Tuning Voltage from the Tune Control Board (A10) plus the +150 VDC
(approx.) output of the HV Converter (A14A2), the circuit shapes the high voltage tuning volt-
age. The shaping is required due to the non-linear voltage vs frequency characteristics of the va-
ractors. The shaping allows a more linear input tuning voltage vs frequency characteristic to be
obtained.
C-4.6 A2A16A4 LO Amplifier Module
(Refer to Figure H.11)
The LO Amplifier Module amplifies the LO output of each RF Frequency Band for use
by the Prescaler Module (A12).
C-5.0 A3 IF Amplifier Module
(Refer to Figure H-13)
The IF Amplifier Module amplifies the selected IF signal plus shapes and sets the IF
bandwidths for the receiver. The module contains three separate IF amplifier subassemblies:
a. A3A1: 175 kHz IF
b. A3A2: 1.6 MHz IF
c. A3A3: 8.7 MHz IF.