3848

DUAL-CONVERSION AM RECEIVER

DISCONTINUED

PRODUCT

—

FOR

REFERENCE

ONL

Y

MIX 2 E

B

13

8

9

10

24

25

26

STOP

MIX 1 IN

CRYSTAL

AGC RATE 2

MIX 2 OUT

DET

WB

AGC

Dwg. PS-012-1

AFC OUT

IF

AGC (MUTE)

REGULATOR

6

7

27

28

MIX 2 OUT

FSI

5

29

B

A

11

22

23

WB AGC 1 IN

MIX 2 E

B

21

RESET

MIX 2

BYPASS

12

SUB

3848

Dwg. No. PS-012-1

DUAL-CONVERSION AM RECEIVER

Providing the AM signal processing functions for an electronically

tuned AM receiver (ETR), the A3848EEQ includes two balanced

mixers, a crystal local oscillator, an L/C-tuned local oscillator, oscillator

buffer, IF amplifier, AM detector, scan control detectors, and a switch-

able voltage regulator. This dual-conversion device typically mixes the

incoming RF up to a first IF of 10.7 MHz, then down to 450 kHz, and

then detects the audio. The addition of a JFET matched to a whip

antenna, RF low-pass filter, IF selectivity, and audio stages gives a

complete AM radio which can be used in automotive receivers. The

frequency-detecting stop circuit is also capable of recovering narrow-

band FM, making it useful for scanners or weather band radio applica-

tions. Two AGC and field-strength indicator modes provide special

features for scanning.

The A3848EEQ uses the dual criteria of frequency and amplitude

for establishing a valid stop. Tuning accuracy (frequency criterion) is

established by evaluating phase shift across the detector coil. The

circuitry is similar to that used in FM discriminators. Because this

detection system is phase operated, it remains effective even in the

presence of strong signals, which can cause false stops in systems

using narrow-band filters. The amplitude criterion for stop is deter-

mined by evaluating the IF level. It includes a unique circuit that

removes the effect of the AGC action. This allows the AGC tuning

components to be selected for low-frequency audio performance

without compromising scanning speed.

In the normal AGC mode (AGC RESET low), a slow, narrow-band

field-strength indicator (FSI) is provided for controlling signal-depen-

dent functions such as stereo blending. A fast AGC mode (AGC

RESET high) resets the AGC holding capacitors to maximum gain.

This mode allows cataloging station strengths quickly during a band

sweep.

This AM signal processor is packaged in a rectangular, 32-lead,

plastic, leaded chip carrier (PLCC) for surface-mount applications and

is rated for operation over the temperature range of -40

°C to +105°C

are available on special order.

FEATURES

s Low Noise Figure

s Field-Strength Indicator

s Balanced Mixers

s Buffered Oscillator

s High Dynamic Range First Mixer s Fast Scan Mode

Always order by complete part number: A3848EEQ .

ABSOLUTE MAXIMUM RATINGS

Operating Temperature Range,

Storage Temperature Range,