Section 4. THEORY OF OPERATION - TM-11-5820-917-130059

TM 11-5820-917-13

SECTION 4

THEORY OF OPERATION

INTRODUCTION

4-2. This section of the manual contains descriptions of the circuits which comprise

the RCS-4B receiver. System and functional block diagrams are included to aid in

understanding operation of circuits and subsystems. Detailed schematic diagrams are

included as foldouts.

4-3. FUNCTIONAL DESCRIPTION

4-4. The RCS-4B receiver consists of three rack- mounted units as shown in figure

4-1. The 6025 control/display (unit 1) contains the circuit modules that perform

timing and control functions and process the baseband signal and AGC voltage (from

the 4028 receiver) to produce an ionospheric sounding record with an AGC bargraph

on the 6025 CRT display. Also on the 6025 is a numeric display of system time,

receiver tuned frequency and path in progress. The 4028 receiver (unit 2) is a

synthesized heterodyne HF receiver that receives the chirp signals on one of three

antenna inputs via power dividers in the 6043 unit. The triple conversion receiver

produces a baseband signal suitable for spectrum analysis. All local oscillator mixer

injections are derived from a phase-locked loop synthesizer. The 6043 power divider

(unit 3) uses three separate four-way power dividers to provide the 4028 receiver

with three antenna connections and to furnish up to three additional antenna connec-

tions for use with communications receivers. The functional elements and inter-

connections of receiver units and assemblies are shown in the block diagrams of

6025 CONTROL/DISPLAY UNIT (UNIT 1)

4-6. The 6025 unit comprises five major functional sections as shown in figure 4-1.

Also, included are voltage regulators, a standby battery supply, front panel controls,

and the receiver self-test circuit. The frequency standard function is provided by

assembly 1A6 which contains two circuit cards and an oven-enclosed crystal

oscillator. As another functional section, the spectrum analyzer circuits are in a

single module (1A1) containing two circuit card assemblies. The receiver control

section includes the 3-path controller module (1A 4) and the auto/sync circuits which

are part of assembly 1A5. The 3-path controller module contains two circuit card

assemblies. Considered part of the CRT display section are the circuits of the dis-

play logic module 1A2, display memory module 1A3, and CRT display module 1A7.

Both the 1A2 and 1A3 modules contain two circuit card assemblies while 1A7 module

contains one circuit card assembly.

The numeric display module 1A9 contains two circuit cards. The 6025 Control/Display

provides all control and timing signals for the 4028 Receiver. The 6025 analyzes the

received signal for display of real time ionospheric conditions. These signals are

displayed on a front panel CRT, producing an easily interpreted Chirpsounder record,

or ionogram. The descriptions that follow for the 6025 circuits are grouped by func-

tional section.

4-1