This is the summary notes of the important terms and concepts in Chapter 5 of the book "Electronic Communications System" by Wayne Tomasi. The notes are properly synchronized and concise for much better understanding of the book. Make sure to familiarize this review notes to increase the chance of passing the ECE Board Exam.
The reverse process of AM modulation.
The first stage of the receiver of which primary functions are
detecting, band limiting, and amplifying the received.
This section down-converts the received RF frequencies to
intermediate frequencies (IFs).
Mixer / Converter
This section primary functions are amplification and
This section demodulates the AM wave and converts it to the
original information signal.
This section amplifies the recovered information. Comprises
several cascaded audio amplifiers and one or more speakers.
A receiver parameter that is used to measure the ability of
the receiver to accept a given band of frequencies and reject all others.
The ratio of the bandwidth 60dB below maximum signal level and
bandwidth 3dB below maximum signal level.
The most prevalent form of noise and is directly proportional
Noise reduction ratio achieved by reducing the Bandwidth.
The corresponding reduction in the noise figure due to the
reduction in bandwidth expressed mathematically in dB.
Noise Figure Improvement
The ________ of a receiver is the minimum RF signal level that
can be detected at the input to the receiver and still produce a usable
demodulated information signal. Also known as receiver threshold.
Defined as the difference in decibels between the minimum
input level necessary to discern a signal and the input level that will
overdrive the receiver and produce distortion.
Defined as the output power when the RF amplifier response is
1 dB less than the ideal linear-gain response.
1-dB Compression Point
A measure of the ability of a communication system to produce,
at the output of the receiver, an exact replica of the original source
Any frequency, phase, or amplitude variations that are present
in the demodulated waveform that were not in the original information signal.
The total phase shift encountered by a signal and can
generally be tolerated as long as all frequencies undergo the same amount of
Absolute Phase Shift
Occurs when different frequencies undergo different phase
shifts and ay have a detrimental effect on a complex waveform.
Differential Phase Shift
Defined as the ratio of the power transferred to a load with a
filter in the circuit to the power transferred to a load without the filter.
( IL )
A hypothetical value that cannot be directly measured. A
parameter that is used in low-noise, sophisticated radio receivers rather
than noise figure.
Equivalent Noise Temperature
The frequencies generated in the receiver and used for
demodulation are synchronized to oscillator frequencies generated in the
Coherent / Synchronous Receiver
Either no frequencies are generated in the receiver or the
frequencies used for demodulation are completely independent from the
transmitter’s carrier frequency.
Noncoherent / Asynchronous Receiver
One of the earliest types of AM receivers and are probably the
simplest designed radio receivers available today.
Tuned Radio Frequency
A phenomenon at radio frequencies where current flow is
limited to the outermost area of a conductor.
A technique where TRF receiver’s instability can be reduced
somewhat by tuning each amplifier to a slightly different frequency, slightly
above or below the desired center frequency.
Means to mix two frequencies together in a nonlinear device or
to translate one frequency to another using nonlinear mixing.
A broad –tuned bandpass filter with an adjustable center
frequency that is tuned to desired carrier frequency.
The most common intermediate frequency used in AM
broadcast-band receivers is ________.
Consists of a series of IF amplifiers and bandpass filters and
is often called IF strip.
Refer to frequencies that are used within a transmitter or
receiver that fall somewhere between the radio frequencies and the original
source information frequencies.
Means that the two adjustments are mechanically tied together
so that a single adjustment will change the center frequency of the
preselector and, at the same time, change the local oscillator frequency.
When the local oscillator is tuned above the RF it is?
High-side Injection / High-beat Injection
When the local oscillator is tuned below the RF it is?
Low-side Injection / Low-beat Injection
The side frequencies undergo a sideband reversal during the
heterodyning process called?
The ability of the local oscillator in a receiver to oscillate
above or below the selected radio frequency carrier by an amount equal to the
intermediate frequency throughout the entire radio frequency band.
The difference between the actual oscillator frequency and the
Any frequency other than the selected radio frequency carrier
that, if allowed to enter a receiver and mix with the local oscillator, will
produce a cross-product frequency that is equal to the intermediate
A numerical measure of the ability of a preselector to reject
the image frequency.
Image-frequency Rejection Ratio
Occurs when a receiver picks up the same station at two nearby
points on the receiver tuning dial.
A high-gain, low-noise, tuned amplifier that, when used, is
the first active stage encountered by the received signal.
High-performance microwave receivers require a ________ as the
input stage of the RF section to optimize their noise figure.
Low-noise Amplifier ( LNA )
A FET with a metal-semiconductor junction at the gate of the
device, called a Schottky barrier.
MEsa Semiconductor FET Semiconductor FET (
A wideband, unconditionally stable, low-power, dual-gain
linear integrated-circuit RF amplifier manufactured by Signetics Corporation.
NE / SA5200
This section purpose is to down-convert the incoming radio
frequencies to intermediate frequencies proportional to bandwidth.
Mixer / Converter Stage
The difference between the level of the IF output with an RF
input signal to the level of the IF output with an IF input signal.
A configuration where the mixer excites itself by feeding
energy back to the local oscillator tank circuit to sustain oscillations
A low-power VHF monolithic double-balanced mixer with input
amplifier, on-board oscillator, and voltage regulator.
NE / SA602A
Are relatively high-gain amplifiers that are very similar to
RF amplifiers, except that IF amplifiers operate over a relatively narrow,
fixed frequency band.
( IF ) Amplifier
The most common technique used for coupling where the voltage
that is applied to the primary windings of a transformer is transferred to
the secondary windings.
Inductive or Transformer
Ability of a coil to induce a voltage within its windings.
Ability of one coil to induce a voltage in another coil.
The ratio of the secondary flux to the primary flux.
Coefficient of Coupling
The transfer of flux from the primary to the secondary
windings and is directly proportional to the coefficient of coupling.
The point where the reflected resistance is equal to the
primary resistance an d the Q of the primary tank circuit is halved and the
Is caused by the reactive element of the reflected impedance
being significant enough to change the resonant frequency of the primary
The coefficient of coupling approximately 50% greater than the
critical value yields a good compromise between flat response and steep
IF transformers come as specially designed tuned circuits in
groundable metal packages called _______.
A differential cascoded amplifier designed for use in
communications and industrial equipment as an IF or RF amplifier at
frequencies from dc to 120 MHz.
The function of this circuit is to demodulate the AM signal
and recover or reproduce the original source information.
A simple noncoherent AM demodulator using a diode. Also called
as diode, shape, or envelope detector.
A distortion in the detection process where the RC time
constant is too short, the output waveform resembles a half-wave rectified
A distortion in the detection process where the RC time
constant is too long, the slope of the output waveform cannot follow the
trailing slope of the envelope.
A circuit that compensates for minor variations in the
received RF signal.
Automatic Gain Control
( AGC )
It prevents the AGC feedback voltage from reaching the RF or
IF amplifiers until the RF level exceeds a predetermined magnitude.
Is similar to conventional AGC except that the receive signal
is monitored closer to the front end of the receiver and the correction
voltage is fed forward to the IF amplifiers.
Its purpose is to quiet a receiver in the absence of a
Are used to remove sporadic, high-amplitude noise transients
of short duration, such as impulse noise in the audio section of a receiver.
A method of measuring signal strength relative to noise
strength where an RF carrier modulated 30% by a 1-kHz tone is applied to the
input of the receiver.
Signal-to-Notched Noise Ratio
A National Semiconductor Corporation linear integrated circuit
AM radio chip that has an onboard RF amplifier, mixer, local oscillator, and
IF amplifier stages. An LIC audio amplifier, such as the LM386, and a speaker
are necessary to complete a functional receiver.
This receivers would need only two external components: a
volume control and a station tuning control.
The ratio of the demodulated signal level at the output of the
receiver (audio) to the RF signal level at the input to the receiver, or the
difference between the audio signal level in dBm and the RF signal level in
Net Receiver Gain
Includes all the gains and losses incurred by a signal as it
propagates from the transmitter output stage to the output of the detector in
the receiver and includes antenna gain and transmission line and propagation