Zubair Tahir
2020F-TE-005
Project Report
INTRODUCTION;
AM Receiver;
To begin with, AM stands for amplitude modulation. It is a strategy of electronic
communication used in the transmission of data. Often, the most used transmission
medium is via a radio carrier wave. However, in this modulation strategy, the radio
carrier wave changes in amplitude with each message signal it transmits.
Therefore, the AM or radio receiver is an electronic device for receiving radio waves and
making them usable. These could be moving images, digital data, or sound. However,
more common is in reproducing sound transmitted via radio broadcasting stations.
AM receivers are of two stages: intermediate frequency and radiofrequency. For
example, using a common-base Armstrong oscillator of the variable frequency helps
you send RF to an IF receiver. Although, this variable frequency is different from the RF
carrier frequency.
However, tuning to the receiver channel simultaneously adjusts the RF and adjacent
oscillator signals. Therefore, you have stations providing fixed carrier frequency to
enable sufficient selectivity.
Types of AM Receivers;
In most cases, the primary AM receivers in existence are of superheterodyne design.
A typical superheterodyne AM receiver comprises six components namely :
a radio frequency amplifier,
a wire antenna,
an IF section,
a mixer/local heterodyne oscillator,
a detector/amplifier.
Furthermore, the above subsystems are crucial for building a radio receiver. For
instance, we have the simpler tuned radio frequency circuit or a TRF electronic amplifier
circuit.
So, going on, we elaborate more on the types of AM receivers which include:
1. TRF Amplifier.
2. AM Detection.
3. Superheterodyne AM radio receiver.
TRF Amplifier
Usually, a radio frequency amplifier has a design that receives a narrow band of
frequencies. One example of this narrow-band frequency is an AM band with a single
radio station.
So, to achieve short wave bands from the tuned circuit, you adjust the resonant
frequency. In addition, the input filter helps you exclude any unwanted input signal.
By default, though, the frequency range of AM shortwave bands is between 500kHz to
1500kHz. Therefore, with the baseband signal at about 5kHz, each station needs at
least 10kHz within this spectrum.
In conclusion, there is a variation in bandwidth with the tuning of the circuit.
(A block diagram illustrating the operation of a tuned radio frequency receiver).
Superheterodyne Receiver
This radio receiver is responsible for boosting the RF audio signal sent to the mixer.
Generally, it amplifies several stations simultaneously, though with an amplified input
noise ratio. Still, it enables tuning in broadcast bands.
On the other hand, the mixer has another input in high-frequency sine sound waves.
This result is largely due to the action of the local heterodyne oscillator. However, these
sine sound waves are often above 455kHz (the standard station carrier frequency for
AM receivers). So, the mixer combines inbound carrier waves with the oscillator to
resolve this. As a result, it then creates a sum and difference frequency.
(A block diagram of a superheterodyne receiver o
However, an ideal mixer combines two weak signals and brings about a couple of new
frequencies. These include:
The original dual frequencies.
A DC level.
Harmonics of the dual input frequencies.
The sum and difference of these two frequencies.
As well as the sum and difference of the fundamental harmonics.
The two primary station frequencies are the Local Oscillator Frequency and Image
Frequency respectively.
AM Detection
We have the coherent radio receiver among the basic AM detection techniques and the
non-coherent one. However, the more straightforward approach is the non-coherent
type of radio receiver.
By contrast, the non-coherent method does not depend on carrier signal regeneration.
With the aid of a diode and electronic audio filters, you detect and remove the
modulation envelope.
On the other hand, the coherent detector stage depends on regenerating and mixing the
carrier and AM signals.
In general, AM detection is into three such as:
Envelope detector.
Square detector.
Synchronous detector.
(A circuit diagram of the envelope detector. It shows the connections of a bypass
capacitor in parallel to the coil and a diode in series).
2. How to Construct a Simple AM receiver
circuit
To construct a simple AM radio receiver circuit, you first need to assemble a few
hardware components, thus:
(A top view of a simple AM radio receiver circuit using five transistors).
Materials needed for the circuit
Circuit Design
Furthermore, we illustrate the design of a simple AM receiver circuit with the aid of a
video attached below.
Circuit Operation
(A schematic showing a simple AM radio model).
So before constructing a simple AM receiver circuit, it is essential to have a good
understanding of its working principles. For that reason, we have included a block
diagram above for visual representation.
For the primary circuit, you need a single transistor, a 365pF variable capacitor, and the
coil L, amongst others. These essential passive components, in conjunction, help to
send signals via the wire antenna. Therefore, they work as a signal receiving cable.
Going further, the OA91 diode D1 identifies the original radio signal. However, the
signal is relatively insignificant. As a result, the BC547 transistor amplifies the weak
signal.
On the other hand, you need a coil L of 80turns of 26 s.w.g. So, you may twist the
enameled copper coil of wire on a cardboard tissue paper roll to achieve this.
Otherwise, open up an AM compact radio and use the coil wound inside.
In summary, a fully functional radio receiver requires an RF component area, the IF
section, and a mixer (RF-to-IF converter). Also, it requires a demodulator and, of
course, an audio speaker.
The demodulator, though, only functions with an incoming radio signal when converted.
And this conversion of incoming radio signal is from carrier frequency to intermediate
frequency. In the end, the radio receiver optimizes and utilizes the converted audio
frequency.
3. AM Receiver Applications
Typically, a simple AM receiver detects amplitude fluctuations in radio waves. An
example is in a crystal radio circuit like the customized crystal earpiece. Here, it
operates at a frequency response resulting in amplification changes in signal voltage.
Other applications include:
In electronic analog telecommunication systems.
Another common use is in the wireless transmissions of data via radio waves.
In addition, it is crucial in AM radio broadcast bands and radio communication.
Also, for use in analog mixers used in audio control.
It is vital for use in two-way aircraft radios.
Furthermore, it is a significant part of devices like computer modems, remote controls, etc.
For use in dispatch radio systems of the navy and police.
Also, there are some outdated applications of AM receivers. Some include telephones,
transmitting Morse codes, controlling television screen pixels, etc.
Conclusion
The AM receiver is an electronic system for modulating amplitude signals. AM receivers
are a mainstay in modern technology because they are essential in radio listening and
other radio transmission applications. Other diverse uses range from radio
communication and data transmission to audio amplification.
Now, we have learned how to build a simple AM receiver. However, if you need further
directions on handling more complex projects, contact our team for assistance.
