Receiver Nonot Harsono,MT

Introduction

• Two important specifications are fundamental to all receivers:

– Sensitivity: signal strength required to achieve a given signal-to-noise ratio

Receiver Topologies

• Nearly all modern receivers use the

superheterodyne principle

• The simplest receiver would consist of a

demodulator connected directly to an antenna • Adding a tuned circuit would improve the

The Superheterodyne Receiver

• The superheterodyne receiver was invented in 1918 by Edwin H. Armstrong and is still almost universally used

• A superheterodyne receiver is characterized by

Functional Elements of

Superheterodyne Receivers

• The input filter and RF stage are referred to as the

Front End of a receiver

• The _mixer combines the signal frequency with a sine-wave signal generated by a local oscillator

Receiver Characteristics

• Sensitivity - the ability to receive weak signals with an acceptable signal-to-noise ratio

• One common specification for AM receivers is the signal strength required for a 10-dB signal-plus-noise-to-noise ratio at a specified power level

• Adjacent channel sensitivity is another way of specifying selectivity

Receiver Characteristics: Distortion

• Distortion comes in several forms:

– Harmonic distortion is when the frequencies generated are multiples of those in the original signal

– Intermodulation distortion occurs when frequency

components in the original signal mix and produce sum and difference signals

Dynamic Range

• The ratio between between the receiver’s response to weak signals and signals that are overload one or more stages is referred to as Dynamic Range

• _{Blocking may occur when two adjacent signals, one of}

Spurious Responses

• Superheterodyne receivers have a tendency to receive signals they are not tuned to

Demodulators

• The demodulator, also known as the detector, is the part of the receiver that recovers the baseband signal. It performs the inverse operation to the

transmitter modulator

Full-Carrier AM

• The simplest, most popular demodulator for full-carrier AM is the _{envelope detector}

SSBSC AM

• A diode detector alone will not work for SSB or DSBSC because the envelope is different from that of AM

FM

• FM demodulators must convert frequency variations of the input signal into amplitude variations at the output

FM Detectors

• There are four major types of FM detectors:

– Foster-Seely discriminator – Ratio detector

Communications Receivers

• The term communications receiver is used mainly for general-purpose receivers that cover a wide range of frequencies from 100 kHz to 30 MHz

Components of

Communications Receivers

• Squelch - disables the receiver audio in the absence of a signal • Noise limiters typically use a diode limiter or clipper in the audio

Transceivers

• A transceiver is simply a transmitter and receiver in one box

• Transceivers are convenient and allow certain economies to be made

Receiver Measurements

• Sensitivity - measured with a calibrated RF signal generator and audio voltmeter