Section 4. Theory of Operation - TM-11-5820-918-130047

TM 11-5820-918-13

SECTION 4

THEORY

OPERATION

4-1.

INTRODUCTION

4-2. GENERAL. The TCS-4B Transmitter consists of three modular units mounted

within an environmentally protective case. The physical arrangement of circuits with-

in the units is functionally oriented. Unit 1, the 1024 Transmit Sweep Generator, con-

tains the transmitter control circuits and provides a sweeping, low-level exciter signal

to the power amplifier unit. Unit 2, the 5018 Power Amplifier, comprises the drive and

output amplifier circuits that provide up to 100 watts output (50 dB gain) of the low-

level RF sweep signal from the 1024 Transmit Sweep Generator. Unit 3, the 4011

Filter/Diplexer, contains the output low pass filters and antenna switching circuits.

Each of the units is supplied with primary line voltage and contains regulated power

supplies.

4-3. FUNCTIONAL DESCRIPTION. The TCS-4B Transmitter is a broadband, EM/CW,

oblique sounder whose output is swept over a frequency band of 2 to 16 MHz, or 2 to

30 MHz, as selected by front panel control. The transmitter is tuned by a digital

synthesizer which is synchronized with an associated RCS-4B Receiver. The synthe-

sizer sweep rate is either 50 kHz/sec for 2-16 MHz range or 100 kHz/sec for 2-30 MHz

range for a constant sweeping time of 280 seconds.

4-4. The transmitter with associated, remotely located receiver and spectrum monitor

functions as an on-line test set for continuous channel measurement of path loss, time

dispersion, noise, and interference over the 2 to 30 frequency range. The measure-

ment function can be performed continuously and in parallel with transmissions of an

operational communications transmitter/receiver system using a common antenna via

the TCS-4B diplexer unit. The transmitter sweeps the complete band repeatedly at

five-minute intervals or can be preprogrammed by front panel switches to skip any

five-minute interval. With an actual transmission time of 4 minutes 40 seconds, 20

seconds in each interval are allowed as blank time to accommodate switching at the re-

ceiver which can be operating with up to three different transmitters, thus measuring

three different propagation paths.

4-5. BLOCK DIAGRAM DESCRIPTION (figure 4-1)

4-6. TRANSMIT SWEEP GENERATOR. In the 1024, the timing and frequency synthe-

sis functions originate from a crystal oscillator (oven stablized) in the frequency

standard assembly 1A3. The output of the oscillator provides a stable frequency re-

fernece for the sweep synthesizer assembly 1A1. The frequency reference signal is

also supplied to the transmit logic assembly 1A2 where it is divided down to provide

all system timing.

4-7. In the transmit logic assembly 1A2, the programmer circuit (1A2A 1) divides the

5 MHz reference signal down to 100 kHz for frequency counter timing and then down

to precise one-second pulses to control the sweep generator clock. The programmer

divides the clock time into 5-minute segments and, depending on the setting of front

panel controls, sends a start-sweep pulse to the synthesizer every five minutes. The

programmer circuit interprets nearly all front panel switch functions and sends the

appropriate sweep start, stop, and reset commands to the synthesizer. The other cir-

cuit card in the transmit logic assembly is the frequency counter/blanker (1A2A2).

This circuit counts the synthesizer output, and this count is sent to the numeric dis -

4-1