Electro-Metrics EM-2115, Instruction Manual

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EM-2115 APPENDIX C FUNCTION AND DESCRIPTION
(EM2115C-6)
The IF output from the RF Tuner Module (A2) is applied to the IF Input Connector
(A3J1) of the IF Amplifier Module. A logic command from the Microprocessor Board (A1A3)
activates the selected IF by turning on the -6 VDC supply for the circuit. Only the selected IF is
turned on, the remaining two IF circuits are turned off to prevent loading the active circuit.
The three IF circuits are similar in operation and general configuration with each setting
two of the three bandwidths for each IF. The narrowest bandwidth for each IF is set by the 0.1
Narrowband Module (A6).
The circuitry for each IF Amplifier is divided into three sections.
IF Circuitry Section #1:
This section comprises an input pass band filter, pass band shaping network at the widest
bandwidth of the selected IF, and a wideband amplifier. The input pass band filter allows
only the selected IF signal to be applied to the amplifier. The pass band shaping network
and wideband filter consists of coupling transformers, capacitors, and resistors. A wide-
band amplifier provides the first level of amplification for the circuit.
IF Circuitry Section #2:
This section is a medium bandwidth pass band shaping network. This filter is activated by
a narrowband logic command from the Microprocessor Board (A1A3) and sets the medi-
um bandwidth for the IF selected. If not activated, the IF signal bypasses the filter and is
applied directly to Section #3 of the IF Amplifier circuitry.
IF Circuitry Section #3:
This section contains a pass band shaping network and wideband filter. The network-
filter finishes shaping the IF signal output that was started in Section #1. An output sec-
tion presents the proper impedance to the 0.1 Narrowband Module (A6).
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 0.1
Narrowband Module (A6).
C-6.0 A6 (0.1) Narrowband Filter Module
(Refer to Figure H.14)
The 0.1 Narrowband Module provides the third and narrowest bandwidth for the IF se-
lected.