Electro-Metrics EM-2115, Instruction Manual

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EM-2115 APPENDIX C FUNCTION AND DESCRIPTION
(EM2115C-7)
As with the IF Amplifier Module (A3), only the IF selected is turned on, the remaining
two IF circuits are turned off to prevent loading the active circuit. A logic command from the
Microprocessor Board (A1A3) activates the selected IF by turning on the -6 VDC supply for the
circuit.
The three IF circuits are similar in operation and general configuration. A crystal filter
sets the narrowest bandwidth for the IF selected.
An amplifier circuit, located after the crystal filter, balances the insertion loss through the
filter circuit. This allows the 0.1 Narrowband Module to maintain a 0 dB insertion loss between
the IF Amplifier (A3) and Log Detector (A4) Modules.
A bypass circuit is activated whenever the narrowest bandwidth is not selected. Adjust-
ments within each bypass circuit are used to balance out the insertion loss, maintaining an overall
0 dB loss through the module.
A separate output connector for each IF circuit applies the amplified and bandwidth de-
fined IF signal (through a subminiature coaxial cable) to corresponding connectors on the Log
Detector Module (A4).
A fourth output connector supplies all three IF outputs to the rear panel POST IF Output
Connector (A13J11).
C-7.0 A4 Log Detector Module
(Refer to Figure H.15)
The Log Detector Module provides a log video output with a range of approximately 90
dB for the receiver.
The module contains three separate log detector subassemblies:
a. A4A1: 175 kHz IF
b. A4A2: 1.6 MHz IF
c. A4A3: 8.7 MHz IF.
As with the IF Amplifier Module (A3), only the log circuit selected is turned on, the re-
maining two log circuits are turned off to prevent loading the active circuit. A logic command
from the Microprocessor Board (A1A3) activates the selected log circuit by turning on the -6
VDC supply for the circuit.
The three log circuits are similar in operation and general configuration.