Specifications

ManualsBrandsEricsson ManualsComputer equipmentDRC-200

THEORY OF OPERATION

GENERAL INFORMATION

The Repeater circuitry is distributed on five PC boards

as follows:

a. Main PC Board containing the receiver section and

transmitter/audio control section

b. Microprocessor/Display PC Board.

c. Control PC Board which contains the audio and

squelch controls,

d. PA PC Board.

e. Power Supply module.

MAIN BOARD

RECEIVER SECTION

The receiver section uses 13.8 V DC from the Power

Supply module for the audio power amplifier

U404

. All

other circuits use regulated +10.0 volts from

U405

U408

, regulated +5.0 volts from

U406

U407

, or regulated

-5.0 volts from the transmitter section.

The RF signal enters the receiver section via a 3 pole

helical resonator filter

L401

and is amplified by a low noise,

wide dynamic range RF amplifier formed around

Q401

The signal then passes through a 4 pole helical resonator fil-

ter

L404

before being feed to a double balanced mixer

HY401

The receiver fractional-n synthesizer IC

U403

receives

its frequency information from the microprocessor

U201

the Microprocessor/Display board. The synthesizer uses a

12.8 MHz TCXO (2.5 PPM temperature compensated crys-

tal oscillator)

Y402

as the reference for the synthesizer fre-

quency. The error voltage from the synthesizer IC is filtered

by a passive loop filter before being applied to the VCO

(voltage controlled oscillator) formed around

Q404

. The

VCO operates at the local oscillator injection frequency

21.4 MHz below the receive frequency. The VCO is buff-

ered by

Q405

and amplified by

Q406

Q407

acts as a con-

stant current source for

Q406

to regulate the local oscillator

injection level to the mixer. The output of

Q406

is coupled

to the double balanced mixer

HY401

The desired output of mixer

HY401

is at 21.4 MHz and

is buffered by

Q402

before being coupled to a 21.4 MHz six

pole crystal filter

XF401

. The filtered output is amplified

Q403

before being applied to

U401

. Inside

U401

, the

21.4 MHz signal becomes the input to a second mixer with

an LO frequency of 20.945 MHz as determined by

Y401

The second mixer output at 455 kHz is filtered by a six pole

ceramic filter,

CF401

, then internally amplified and applied

to an FM detector. The detector output level is maximized

through adjustment of the quadrature detector coil

L409

The detected audio is buffered by

U402D

before being

routed to the Microprocessor/Display PC Board.

The detected audio from

U402D

is also routed to the

Squelch control

R102

on the Control PC Board. The center

arm of the squelch control is routed to a high pass filter and

an amplifier internal to

U401

’s output is routed to

an additional high pass filter

U409B

before being rectified

CR401

. The amount of ultrasonic noise on the detected

audio from

U401

is used to determine the presence of an RF

carrier. The DC voltage from

CR401

is routed to the Mi-

croprocessor/Display PC Board as an input to the micro-

processor

U201

U404

is the audio power amplifier which drives either

the internal speaker or an external speaker.

TRANSMITTER/AUDIO CONTROL

SECTION

This section contains the -10.0 volt regulator

U514

whose output is further regulated to -5 volts by

U515

. The

negative (–) 5 volt output is used by both the transmitter and

the receiver VCO’s. There are two +5.0 volts regulators

U510

and

U511

, as well as a +10.0 volt regulator

U513

, and

a switched +10.0 volt regulator

U512

used for the transmit

VCO and transmit driver sections.

The unit has provisions for connecting local microphone

audio, remote station audio, interconnect audio, data or re-

peat audio to the transmitter’s modulation circuitry. These

audio signals, plus DCS, CTCSS or external tones, are con-

trolled by information from the microprocessor

U201

on the

Microprocessor/Display PC Board.

The microphone, remote, interconnect, data, and repeat

audio signals are routed through a preamp section before be-

ing connected to the multiplexer

U502

. The preamp sec-

tions are

U503B

for local microphone audio,

U501A

with

gain adjustment

R553

for remote station audio,

U501D

with

gain adjustment

R548

for interconnect audio,

U503A

for

buffering data and

U501B

with gain adjustment

R507

for

repeat audio. The output of the multiplexer is routed to

U507B

U507C

and

U507D

which form a limiter and two

stage (four pole) low pass filter. A master deviation control

R544

sets the signal level for the VCO modulation input

while the balance adjustment

R538

sets the level for the

AE/LZB 119 1882 R1B