QUEZON CITY POLYTECHNIC UNIVERSITY

673 Quirino Highway, San Bartolome Novaliches, Quezon City

Electronics Engineering Directory

PROJECT IN PRINCIPLES OF COMMUNICATION

“AM RADIO RECEIVER”

SBEE – PET 1

Leader: AGUILAR, PATRICIA MAE D.

Members:
ACOSTA, LESTER MARK R.
ANTONIO, REINIEL C.
AMORSOLO, SAM ANDERSON A.

DELOS SANTOS, JEROME JOHN G.

INSTRUCTOR:

ENGR. LEONARD CATCHILLAR

I. OBJECTIVES

 To build up a good AM radio receiver.

 To be able to tuned at least 10 AM Radio stations.
 To be able to understand how AM radio receiver functions.
 To familiarized the functions of each components and connections.

II. THEORETICAL FRAMEWORK

Radio technology is an integral part of everyday life. Everything from broadcast radio
and television through to mobile phones, wireless connectivity, Internet of Things and much
more are based around radio technology. AM (Amplitude Modulation) and FM
(Frequency Modulation) are ways of broadcasting radio signals. Both transmit the information
In the form of electromagnetic waves. AM works by modulating (varying) the amplitude of the
Signal or carrier transmitted according to the information being sent, while the frequency
Remains constant. The differs from the FM technology in which information (sound) is encoded
by varying the frequency of the wave and the amplitude is kept constant.

AM and FM modulated signals for radio. AM (Amplitude Modulation) and FM

(Frequency Modulation) are types of modulation (coding). The electrical signal from
program material, usually coming from a studio, is mixed with a carrier wave of a
specific frequency, then broadcast. In the case of AM, this mixing (modulation) is done by
altering the amplitude of the carrier wave with time, according to the original signal. In the case
of FM, it is the frequency of the carrier wave that is varied. A radio receiver (a "radio") contains
a demodulator that extracts the original program material from the broadcast wave. When
you extend the antenna (aerial) on a radio receiver, it snatches some of the
electromagnetic energy passing by. Tune the radio into a station and an electronic circuit
inside the radio selects only the program you want from all those that are broadcasting.

History of Radio Receiver

This form of receiver is based around the idea of mixing signals in a non-linear fashion.
This idea was first noticed when beats were detected between two signals. R A Fessenden was
the first person to notice this and he patented the idea in 1901. However the idea lay dormant
for some years as most receivers consisted of detectors and tuned circuits. The diode
thermionic valve or vacuum tube was invented by Ambrose Fleming in 1904, and then a third
grid was added by Lee de Forest. Although early valves or tubes were in use, they were very
unstable and it was difficult to gain much useful performance from them.

A young engineer named Edwin Armstrong started to utilize the power of the vacuum
tube or thermionic valve, inventing the regenerative receiver around 1910. This provided a
considerable increase in useful gain over what was previously attained.
It was the onset of the Great War in 1914 that gave fresh impetus to radio receiver
design. There was a requirement for sensitive radio receivers for a variety of tasks. The first
major step was taken by a Frenchman named Lucien Levy. At the time the performance of
valves was very poor at frequencies above 100 kHz or so, and he devised a system for
reducing the frequency of the incoming signal using the system of beats - the signal could then
be tuned and amplified more effectively at a lower frequency.
Edwin Armstrong came to the fore again, by developing the superhet or
superheterodyne receiver as we know it today with a fixed frequency intermediate frequency
filter and a variable local oscillator. His idea was developed in 1918, right at the end of the war,
and as a result it was not widely used.
After the war it was discovered that similar receivers were postulated by the Germans,
but none were actually made. As a result, Edwin Armstrong was credited with the invention.
The superheterodyne receiver was not used initially, as it was felt that many valves in the set
did not contribute to providing signal gain, and valves were expensive. However as the number
of broadcast stations increased and selectivity became an issue, along with the falling cost of
thermionic valves, use of the superhet receiver started to grow in the late 1920s and early
1930s. Since then it has been in widespread use.

AM Radio Receiver Technical Details

AM was initially developed for telephone communication. For radio communication,

a continuous wave radio signal called double sideband amplitude modulation (DSB-AM) was
produced. A sideband is a band of frequencies higher (called upper sideband) or lower
(called lower sideband) than the carrier frequencies which is a result of modulation. All forms
of modulations produce sidebands. In DSB-AM the carrier and both USB and LSB are present.
The power usage in this system proved inefficient and led to the double-sideband suppressed
Carrier (DSBSC) signal in which the carrier removed. For greater efficiency, single
sideband modulation was developed and used in which only a single sideband remained. For
digital communication, a simple form if AM called continuous wave (CW).
The international Telecommunication Union (ITU) designated different types of
amplitude modulation in 1982 which include A3E, double sideband full-carrier; H3E,
single sideband full-carrier; J3E, single sideband suppressed-carrier; B8E, independent-
sideband emission; C3F, vestigial-sideband and Lincomplex, linked compressor and expander.

Pros and Cons of AM vs. FM Radio Receiver

The advantages of AM radio are that it is relatively easy to detect with simple equipment,
even if the signal is not very strong. The other advantage is that it has a narrower bandwidth
than FM, and wider coverage compared with FM radio. The major disadvantage of AM is that
the signal affected by electrical storms and other radio frequency interference. Also, although
the radio transmitters can transmit sound waves of frequency up to 15KHz, most receivers
are able to reproduce frequencies only up to 5KHz or less. Wideband FM was invented
to specifically overcome the interference disadvantage of AM radio.
A distinct advantage that FM has over AM is that FM radio has better sound quality
than AM radio. The disadvantage of FM signal is that it is more local and cannot be transmitted
over long distance. Thus, it may take more FM radio stations to cover a large area. Moreover,
the presence of tall buildings or land masses may limit the coverage and quality of FM. Thirdly,
FM requires a fairly more complicated receiver and transmitter than an AM signal does
 AM RADIO RECEIVER BLOCK DIAGRAM

AERIAL

MIXER

IF AMP IF AMP IF AMP

1 2 3

LOCAL
OSCILLATOR

IF Amplifier Stage

Frequency Converter

POWER DRIVER PRE- DETECTOR

AMP AMP AMP

Demodulator Stage
SPEAKER Audio Amplifier Stage

This is a block diagram of AM radio receiver. Most of these blocks are

discussed individually. For AM radio has consecutive stages, The Frequency converter,
amplifier stage, demodulator stage, and audio amplifier stage. The AM band covers 535 –
1605 KHz. Signals enter the receiver from the antenna and are applied to the RF amplifier
where they are tuned to remove the image signal and also reduce the general level of
unwanted signals on other frequencies that are not required.

The signals are then applied to the mixer along with the local oscillator where the
wanted signal is converted down to the intermediate frequency. Here significant levels
of amplification are applied and the signals are filtered. This filtering selects signals on
one channel against those on the next. It is much larger than that employed in the front end.
The advantage of the IF filter as opposed to RF filtering is that the filter can be designed for
a fixed frequency. This allows for much better tuning. Variable filters are never able to provide
the same level of selectivity that can be provided by fixed frequency ones.

Once filtered the next block in the receiver is the demodulator. This could be for
amplitude modulation, single sideband, frequency modulation, or indeed any form of
modulation. It is also possible to switch different demodulators in according to the mode
being received.
 The final element in the receiver block diagram is shown as an audio amplifier,
although this could be any form of circuit block that is used to process or amplified
the demodulated signal.

 Frequency Converter Stage - The converter stage may sometimes be referred to as

the mixer, or first detector stage, the latter being an early term. Tunes and amplifies
the received signal. Generates an unmodulated RF signal at a frequency off-set from
the received signal. Mixes the locally generated signal with the received signal. Maintains
a constant frequency difference between the locally generated frequency and any signal
to which the receiver is tuned.

 IF Amplifier Stage - Accepts the intermediate frequency signal from the converter, amplify
it and pass it on to either, the next I-F stage (if the receiver has one), or to the detector
stage. These stages contain most of the amplification in the receiver as well as the
filtering that enables signals on one frequency to be separated from those on the next.
Filters may consist simply of LC tuned transformers providing inter-stage coupling, or
they may be much higher performance ceramic or even crystal filters, dependent upon
what is required.

 Demodulator Stage - Detector is a device for detecting the presence of

electromagnetic waves or of radioactivity, a rectifier of high-frequency current used
especially for extracting the intelligence from a radio signal. Once the signals have
passed through the IF stages of the receiver, they need to be demodulated.
Different demodulators are required for different types of transmission, and as a result
some receivers may have a variety of demodulators that can be switched in to
accommodate the different types of transmission that are to be encountered.

 AM diode detector: This is the most basic form of detector and this circuit block
would simple consist of a diode and possibly a small capacitor to remove any
remaining RF. The detector is cheap and its performance is adequate, requiring
a sufficient voltage to overcome the diode forward drop. It is also not particularly
linear, and finally it is subject to the effects of selective fading that can be
apparent, especially on the HF bands.

 Synchronous AM detector: This form of AM detector block is used in where

improved performance is needed. It mixes the incoming AM signal with another
on the same frequency as the carrier. This second signal can be developed by
passing the whole signal through a squaring amplifier. The advantages of the
synchronous AM detector are that it provides a far more linear demodulation
performance and it is far less subject to the problems of selective fading.

 SSB product detector: The SSB product detector block consists of a mixer and a
local oscillator, often termed a beat frequency oscillator, BFO or carrier insertion
oscillator, CIO. This form of detector is used for Morse code transmissions
where the BFO is used to create an audible tone in line with the on-off keying of
the transmitted carrier. Without this the carrier without modulation is difficult to
detect. For SSB, the CIO re-inserts the carrier to make the modulation
comprehensible.
 Audio Amplifier Stage - The output from the demodulator is the recovered audio. This
is passed into the audio stages where they are amplified and presented to the headphones
or loudspeaker. Signals enter the receiver from the antenna and are applied to the RF
amplifier where they are tuned to remove the image signal and also reduce the general
level of unwanted signals on other frequencies that are not required.

How the Superheterodyne Receiver works

In order to look at how a superhet or superheterodyne radio works, it is necessary to

follow the signal through it. In this way the processes it undergoes can be viewed more closely.
The signal that is picked up by the antenna passes into the receiver and enters a mixer.
Another locally generated signal, often called the local oscillator, is fed into the other port on the
mixer and the two signals are mixed. As a result new signal are generated at the sum and
difference frequencies.

The output from the mixer is passed into what is termed the intermediate frequency or IF
stages where the signal is amplified and filtered. Any of the converted signals that fall within the
pass band of the IF filter will be able to pass through the filter and they will also be amplified by
the amplifier stages. Any signals that fall outside the passband of the filter will be rejected.

Tuning the receiver is simply accomplished by changing the frequency of the local
oscillator. This changes the incoming signal frequency for which signals are be converted down
and able to pass through the filter.

It is often helpful to look at a real example to illustrate how the process works. To see
how this operates in reality take the example of two signals, one at 1.0 MHz and another at 1.1
MHz. If the IF filter is centred at 0.25 MHz, and the local oscillator is set to 0.75 MHz, then the
two signals generated by the mixer as a result of the 1.0 MHz signal fall at 0.25 MHz and 1.75
MHz. Naturally the 1.75 MHz signal is rejected, but the one at 0.25 MHz passes through the IF
stages. The signal at 1.1 MHz produces a signal at 0.35 MHz and another at 1.85 MHz. Both of
these fall outside bandwidth of the IF filter so the only signal to pass through the IF is that from
the signal on 1.0 MHz.

If the local oscillator frequency is moved up by 0.1 MHz to 0.85 MHz then the signal at
1.1 MHz will give rise to a signal at 0.25 MHz and another at 1.95 MHz. As a result the signal at
1.1 MHz giving rise to the 0.25 MHz signal after mixing will pass through the filter. The signal at
1.0 MHz will give rise to a signal of 0.15 MHz at the IF and another at 1.85 MHz and both will be
rejected. In this way the receiver acts as a variable frequency filter, and tuning is accomplished
by varying the frequency of the local oscillator within the superhet or superheterodyne receiver.

The advantage of the superheterodyne radio process is that very selective fixed
frequency filters can be used and these far out perform any variable frequency ones. They are
also normally at a lower frequency than the incoming signal and again this enables their
performance to be better and less costly. The basic concept of the superheterodyne receiver
appears to be fine, but there is a problem. There are two signals that can enter the Intermediate
frequency stages.

The unwanted signal that can enter the intermediate frequency stages is known as the
image signal. Removing the image signal is a key requirement in the performance of the
superhet radio.
Concept of the Superheterodyne Receiver Image
With the local oscillator set to 0.75 MHz and with an IF of 0.25 MHz, it has already been
seen that a signal at 1.0 MHz mixes with the local oscillator to produce a signal at 0.25 MHz
that will pass through the IF filter. However if a signal at 0.5 MHz enters the mixer it produces
two mix products, namely one at the sum frequency which is 1.25 MHz, whilst the difference
frequency appears at 0.25 MHz. This would prove to be a problem because it is perfectly
possible for two signals on completely different frequencies to enter the IF.
The unwanted frequency is known as the image. Fortunately it is possible to place a
tuned circuit before the mixer to prevent the signal entering the mixer, or more correctly reduce
its level to acceptable value.
This RF tuning circuit does not need to be very sharp. It does not need to reject signals
on adjacent channels, but instead it needs to reject signals on the image frequency. These will
be separated from the wanted channel by a frequency equal to twice the IF. In other words with
an IF at 0.25 MHz, the image will be 0.5 MHz away from the wanted frequency.

Superheterodyne Receiver Image

There are several facts about the superheterodyne receiver image response that can be
summarised quite easily.
Image is twice the IF away from the wanted signal: Frequencies that enter the IF are
spaced from the local oscillator by an amount equal to the intermediate frequency. Therefore if
one frequency is LO + IF, the other one will be LO – IF. The difference between these two is two
times IF, i.e. twice the intermediate frequency. It is for this reason high intermediate frequencies
may be chosen as it improves the image performance.

RF tuning: In order to ensure that the RF tuning does not introduce any undue signal
reduction, and it ensures the image response is reduced by the maximum amount, it tunes in
line with the local oscillator. Thus if the LO increases by 1 MHz then the RF tuning must
increase by the same amount to ensure it tracks the received signal frequency correctly. Early
radio receivers used ganged tuning capacitors consisting of two sections. Attached to the same
spindle the capacitance of each section changed by the same amount enabling the RF tuning to
track at the same rate as the local oscillator.
The superheterodyne receiver image response is a key performance parameter that is
measured in receivers. It is possible to reduce it by significant amounts on high performance so
that it does not cause any major problems. Low cost receivers normally have some problems
although in recent years receiver image performance levels have improved significantly.
III. LIST OF MATERIALS/ EQUIPMENT/ TOOLS

Am Radio Receiver Components:

Resistor  C8,C13 – 100uF/10V
 C10 – 220uF/10V
 R1 – 680KΩ
 C11 - .001uF/50V CER. (102)
 R2 – 1KΩ
(1k)
 R3 – 150KΩ  C12 – 470uF/10V
 R4 – 39KΩ  VC1 – Variable capacitor (AM)
 R5 - 680Ω
 R6 – 560KΩ
 R7 – 560Ω Transistor
 R8 – 4.7KΩ
 R9,R10 – 27KΩ  Q1,Q2,Q3 – ED1402
 R11 - 330Ω  Q4 - 1912
 R12 – 15KΩ  Q5 -1913
 R13 – 1.2KΩ  Q6 - S 8550
 R14 – 5.6Ω  Q7 – S 8050
 R15 – 10KΩ Others
 R16 - 100Ω
 R17 – 180Ω  T1 Antenna coil
 Antenna Bar
Capacitor
 IF Transformer Set
 C1, C4, C5, C7 - (Yel, Blk & Whi )
.02uF/50V CER. (203)  Oscillator coil (Red)
 C2 – .005uF/50V  Antenna Holder
CER. (502)  Volume control
 C3,C9 – 10uF/16V  PCB 2x2 (4 pcs.)
 C6 - .01uF/50V CER.  Detector diode 1N60
(103)

Mono Audio Amplifier Components:

Resistor Capacitor

 R1 – 1MΩ  C1 - 1uF, C10,C16 – 1000uF

 R2, R9 – 1KΩ  C2, C17 - 104
 R3 – 3.3KΩ  C3, C4, C5 – 103
 R4 – 1.5KΩ  C6 – 222, C9 – 470uF
 R5- 10KΩ  C7, C14– 47uF,
 R6 – 560Ω  C8 – 4.7uF, C15 – 33uF
 R7 – 6.8KΩ  C11,C12,C13 – 100uF
 R8 – 15KΩ
Diode – 1N4001 (2pcs.)
 R10 – 56KΩ
 R11 – 470Ω IC – BAS406
Transistor Potentiometer – Volume, Bass, Treble
 C828
Power Supply (6V & 12V DC) Components:

 Transformer 12V 1A
 Diode - 1N4007 (4 pcs.)
 Capacitor - 1000uF (2 pcs.), 0.01uF (4 pcs.), 10uF (2 pcs.)
 IC7812, IC7912, IC7806, IC7906
 PCB (2x2)
 Fuse w/ holder
 Switch

Equipment and Tools:

 Speaker
 Wires
 Battery (6V)
 Printed Circuit Board
 Acrylic Board
 Set of screw
 Switch
 Binding post
 Soldering Iron
 Soldering lead
 Soldering Paste
 Mini drill
 Non-metallic material
(adjusting)
 Pliers (long nose)
 Ferric chloride
 Tester (Analog & Digital)
IV. PROCEDURE / METHODOLOGY
1. Complete all components are needed in this project.
2. Make sure all components were tested and functioning conditions.
3. Study the schematic diagram, block diagram and PCB layout.

A. Construction Guide for AM Radio receiver

1. Design PCB layout for different stages (4 stages).

2. Print and iron in Printed Circuit Board.
3. Insert and solder all Resistors into their respective locations in PCB.
4. Insert and solder all Electrolytic and Mylar capacitor in proper polarity and right
placements.
5. Insert and solder the detector diode into respective locations.
6. Insert and solder all transistor. Be sure the three electrodes are place in proper locations.
7. Insert and solder the IFT, Oscillator coil and Tuning capacitor into their respective
locations. Be careful with the pin configurations.
8. Insert and solder the Antenna coil in proper locations.
9. Mount the volume control into the PCB. Use the excess cut-off lead terminals of
resistors or capacitors to link the potentiometer terminals to that of the PCB.
10. Connect all connecting wires to their respective points in the PCB. The red wire to the
positive supply and the black wire to the switch of the volume control for negative supply.
Excess cut-off lead of resistors may be used in connecting the tuner output to the audio
amplifier input.
11. Mount the antenna coil firmly into its designated place in the PCB using plastic antenna
holders to hold the antenna bar firmly in its place. Be sure to tin the coil terminals before
soldering to their respective PCB points.
12. Connect the speaker terminals to their respective PCB points.
13. Apply a 6-volt supply voltage to the circuit; positive to the red wire and negative to the
black wire.
14. If the receiver functions, proceed to the alignment procedure.

Note: Check everything first. Pay attention all soldered connections. Look for shorts
between adjacent paths or cold soldered connections. You can use mini drill
or cutter to remove shorted connections.
B. Receiver Alignment
Receiver alignment is carried out by adjusting the tuned circuits to their correct
frequencies. There are two parts to the alignment process; IF and RF alignment. First, the IF
transformers must be tuned to the intermediate frequency. The adjustment begins with the last
IF transformer (black IFT) into the detector and works back to the mixer output circuit. The
reason is that the IF signal is checked by observing the detector output. The main requirement
of the IF alignment is setting the local oscillator to tune in the station frequencies in the dial.
This procedure has two parts, one at the low end, either the oscillator coil or the padder
capacitor C1a is adjusted. The trimmer capacitor C1b is used to adjust the frequencies at the
high end.

Pre-alignment:
1. Turn the radio set ON by switching the volume control clockwise.
2. Tune to the station operating at the highest band near the 1,600 KHz.
3. Rotate the radio to a spot with weak signal.
4. Adjust IFT core black slowly back and forth until the maximum volume is achieved.
5. Do the same procedure as to the IFT core white and IFT core yellow for the louder
volume.

Alignment Procedure:
1. A.) Tune to the station operating at 580 KHz. DZXL in Metro Manila or to the station with
the lowest Frequency in your area.
B.) Adjust the oscillator coil (red) with screwdriver. Slowly rotate it in the clockwise
direction until 580 KHz is obtained.

2. A.) Tune to the station operating at 1570 KHz. DZME in Metro Manila or to the station
with the Highest frequency in your area.
B.) Turn the trimmer of the tuning capacitor C1b until it points exactly 1570 KHz. DZME
or to the Highest frequency station in your area.

3. A.) Return to the station 850 kHz or the lowest frequency in your area.
B.) Rotate the radio to a spot with the weaker sound.
C.) At this point, adjust the antenna coil back and forth for maximum signal.

4. A.) Tune to the station operating at 1570 KHz, or to the station with the highest frequency
in your area.
B.) Rotate the radio to a spot with the weaker sound.
C.) Turn the trimmer of tuning capacitor C1a with a screwdriver for maximum signal.
D.) Repeat steps 3 and 4 and alignment is completed.
V. EXPERIMENTAL CIRCUIT SET-UP
A. Schematic Diagram
AM Radio Receiver
Frequency Converter (1st Stage) IF Amplifier Stage (2nd Stage)

Demodulator Stage (3rd Stage)

Mono Audio Amplifier (4th Stage)

B. Parts Placement
AM Radio Receiver
Frequency Converter (1st stage)
Component Side Copper Side

IF Amplifier (2nd stage)

Component Side Copper Side

Demodulator (3rd stage)

Component Side Copper Side
 Mono Audio Amplifier (4th stage)

Test points for AM Radio Receiver

Power Supply
Component Side Copper Side
C. PCB Layout
AM Radio Receiver
Frequency Converter (1st Stage) IF Amplifier (2nd Stage)

Demodulator (3rd Stage) Mono Audio Amplifier (4th Stage)

Actual Complete Output
VI. OBSERVATION
Frequency Converter ( 1st stage )

 The Variable Capacitor (VariCap) serves as the tuning part of the whole Radio, for it
has the variable or changing capacitance with respect to the antenna coil.
 When the Red Intermediate Frequency Transformer (Red IFT) or Local Oscillator is
being tuned, the reception of the RF signal also tuned to better sound output.
 When the antenna coil touches any static material like our hands, the output sound
at the speaker produces noise and undesirable sound.
 The reception of the Radio Frequency (RF) signal changes or distorts when the
antenna coil placed on either side of the antenna bar.

Intermediate Frequency Amplifier ( 2nd stage )

 The output of the first stage serves as the input signal for the second stage.
 The yellow, white and black IFTs help the smoothness of the sound to achieve.
 The output of the third stage is being connected to this stage and it makes the
sound at the output speaker more stable and pleasant.

Detector/Demodulator ( 3rd stage )

 The output of the second stage serves as the input for the third stage.
 The Signal-Diode (1N60) is connected in-reversed bias with respect to the output of
the second stage that selects the signal needed at the amplifier stage.
 The output of this stage is now in audible frequency but low amplitude

Audio-Signal Amplifier ( 4th stage )

 The output after the demodulator will be amplified to this stage.

 When the speaker is now connected to the amplified output of this stage, the
speaker produces distorted sound.
 The potentiometer controls the loudness of the output sound produced by the
speaker.
 The output sound produces undesirable sound. Because, the output from this stage
is connected to the speaker and touched by our finger,
VII. ANALYSIS
Frequency Converter (1st stage)

 In the Radio receiver, the incoming signal through the antenna is filtered to reject
the image frequency and then amplified by the RF amplifier.
 RF amplifier can be tuned to select the desired frequency or station and amplify
a particular carrier frequency within the AM broadcast range. Only the selected
frequency and its two sidebands will be allowed to pass through the amplifier.
 The frequency of local oscillator is not same as the frequency to which RF amplifier
is tuned. Local oscillator is tuned to a frequency that may be either higher or lower
than the incoming frequency by an amount equal to the IF frequency.
 The antenna coil is an inductor that receives the RF signal coming from
different transmitter of radio station in Philippines, particular in Metro Manila.
The distortion is being produced because of the static electricity induced by our hands.
 The antenna bar is made of ferrite where it helps the antenna coil to receive the RF
signal in free-space that is being used by many radio stations.
Intermediate Frequency Amplifier (2nd stage)

 The partial output of the third stage is fed to this stage and it makes the sound at the
output speaker more stable and pleasant.
 The IF signal is amplified with the help of IF amplifier which raises its level for
the information extraction process. Also the IF amplifier fulfils most of the gain
and bandwidth requirements of the receiver.
 IF amplifier operations are independent to the frequency at which receiver is
tuned, maintaining the selectivity and sensitivity of the superheterodyne
receiver considerably constant throughout the tuning range of the receiver.

Detector/Demodulator (3rd stage)

 The Diode eliminates the upper side band of the received signal present in second
stage and separates the RF signal from the audio signal
 The capacitors serve as the high-pass filter where it removed the low-frequency signal
(modulating signal) and passes only the high frequency (carrier signal).
 The RF component is filtered out and audio is supplied to the audio stages for
amplification.
 An important part of Radio receiver is Automatic Gain Control (AGC) which will be fed
to the Radio Frequency, Intermediate Frequency and Mixer stages in order to generate
constant output irrespective of the varying input signal.

Audio-Signal Amplifier (4th stage)

 The output after the demodulator will be amplified to this stage for better audio output
to the speaker.
 The speaker produces distorted sound because the IFT`s are not yet tuned.
 The potentiometer provides the Amplitude-Control or the Volume-Control of the whole
circuit.
 The generated audio signal is then applied to the AF amplifier to increase the audio
frequency level of the signal and to provide enough gain for the speaker or headphones
play its role in the circuit.
 A speaker is connected to the AF amplifier to play the audio information signal.
 AM Radio components Resistance Measurement
A. Resistor

RESISTOR COLOR CODED VALUE MEASURED METER

VALUE RANGE
R1 B, Gy, Y, Go 680KΩ ± 5% 672KΩ R x 2M
R2 Br, Bl, R, Go 1KΩ ± 5% 966Ω R x 2K
R3 Br, Gr, Y, Go 150KΩ ± 5% 148.7KΩ R x 200K
R4 Or, W, Or, Go 39KΩ ± 5% 37.9KΩ R x 200K
R5 B, Gy, Br, Go 680Ω ± 5% 672KΩ R x 2K
R6 Gr, B, Y, Go 560KΩ ± 5% 556KΩ R x 2M
R7 Gr, B, Br, Go 560Ω ± 5% 540KΩ R x 2K
R8 Y, V, R, Go 4.7KΩ ± 5% 4.6KΩ R x 20K
R9 R, V, Or, Go 27KΩ ± 5% 26.7KΩ R x 200K
R10 R, V, Or, Go 27KΩ ± 5% 27.1KΩ R x 200K
R11 Br, Gr, Or, Go 330Ω ± 5% 326Ω R x 2K
R12 Br, Gr, Or, Go 1.5KΩ ± 5% 15KΩ R x 200K
R13 Br, R, R, Go 1.2KΩ ± 5% 1.2KΩ R x 2K
R14 Gr, Gy, Go, Go 5.6Ω ± 5% 5.7Ω R x 200
R15 Br, Bl, Or, Go 10KΩ ± 5% 9.77KΩ R x 20K
R16 Br, Bl, Br, Go 100Ω ± 5% 97.1KΩ R x 2K
R17 Br, Gy, Br, Go 180Ω ± 5% 177.2KΩ R x 200

B. Coils and IF Transformers

TYPICAL READING MEASURED METER

RANGE
1&2 2&3 1&3 4&5 1&2 2&3 1&3 4&5
Red 3 1 3 0.2 4 1 4 1 RX1
( L.O)
Yel 3 1 4 0 2 4 5 1 RX1
IFT
Whi 3 1 4 0 4 2 5 1 RX1
IFT
Blk 2 1.5 3.5 0.4 4 3 7 2 RX1
IFT

C. Capacitors

ACTUAL TRANSISTOR R MEASURED R METER

VALUE CODE READING RANGE
OF Charge Discharge Charge Discharge
CAPACITORS
C1 .02uF/50V CER. G G RX1
203
C2 .005uF/50V CER. G G RX1
502
C3 10uF/16V G Ω R X 2K
 C4 .02uF/50V CER. G G RX1
203
C5 .02uF/50V CER. G G RX1
203
C6 .01uF/50V CER. G G RX1
103
C7 .02uF/50V CER. G G RX1
203
C8 100uF/10V G Ω R X 2K
C9 10uF/16V G Ω R X 2K
C10 220uF/10V G Ω R X 2K
C11 .001uF/50V CER. G G RX1
102
C12 470uF/10V G Ω R X 2K
C13 100uF/10V G Ω R X 2K

D. Transistor

TRANSISTOR TRANSISTOR R READING MEASURED R

CODE RX1 R X 10K RX1 R X 10K
Q1 ED1402 B- C+ B- E+ / B+ E- 0 0 / 18.24
Q2 ED1402 B- C+ B- E+ / B+ E- 0 0 / 18.29
Q3 ED1402 B- C+ B- E+ / B+ E- 0 0 / 17.89
Q4 1912 B- C+ B- E+ / B+ E- 601 17.18 / 0
Q5 1913 B- C+ B- E+ / B+ E- 0 0 / 18.52
Q6 S 8550 B- C+ B- E+ / B+ E- 0 0 /0
Q7 S 8050 B- C+ B- E+ / B+ E- 0 0 / 18.10

E. Other Components

DETECTOR TYPICAL R METER MEASURED METER

DIODE READING RANGE RANGE
A+K- A–K+ A+K- A–K+
1N60 FB RB R X 2K 604 0 R X 2K

ANTENNA TYPICAL R METER MEASURED METER

COIL READING RANGE RESISTANCE RANGE
1&2 3&4 1&2 3&4
1.8Ω 0.2Ω RX1 2.5Ω 0.6Ω RX1

TYPICAL R READING MEASURED RESISTANCE

TUNING CAPACITOR R X 10K R X 10K
Terminal O & G
Terminal G & A
Terminal O & A
VIII. CONCLUSION

 We conclude that studying the schematic diagram of the AM radio receiver will help
us come up with a working principles and its efficiency.
 We realized that in making AM receiver the components must be appropriate and
in proper position. And to know how to adjust the IF and Variable capacitor.
 At first, our project not functioning properly and we decided to used fixed mono
audio amplifier for better process or amplified the demodulated signal.
 We must keep in mind the condition of the components, if it is defective or not
working. Because it can affect in our AM radio receiver.
 Thus, check also the components are soldered properly to avoid shorted.
 The location must take into consideration to achieve better reception, because there
are places where you can receive a good signal and there are also places that
have not.

IX. RECOMMENDATION

1. Circuit analysis is important although the schematic and block diagrams are given, should
the designed PCB layout is correct.
2. When doing the actual Printed Circuit Board soldering you should pay attention to
the connections and the placements of the components.
3. Checking of the components before it is used is also very important because it will
determine your output, faulty components means bad output or even no output at all.
You should make sure that the components to used are in good condition.
4. You need to have knowledge in trouble shooting the AM radio receiver
to determine the damage in case there is a problem on the circuit.
5. Use limited or short wires only for your radio receivers. Because wires can be an antenna
that can enter the signals.
6. The circuit printed design should be ironed properly in your PCB.
7. Be careful on using the soldering iron and make sure that it is placed in an area where
there will be no plastic or other things that you don’t want to melt.
8. Solder the terminals properly and prevent over lead adding to also prevent
unwanted connection. Get rid of the flux by using cutter or mini drill.
9. Be patient in tuning the AM radio receiver.
10. To achieve efficient output, make use of higher wattage of resistors and higher voltage
rating of capacitors.
11. Use non-metallic material for adjusting IF and variable capacitor.
 12. Be careful in rotating your VariCap, be sure to rotate it clockwise first.
13. Be careful in rotating the IF Transformers. In rotating the IF Transformers, please note
the right sequence – RED, BLACK< WHITE and YELLOW.
14. Use earphone for aligning AM radio stations.
15. In testing stage, should be performed in a place where there is enough signal for the Radio
to receive enough signals and to be properly calibrated.

X. REFERRENCES

https://www.radioremembered.org/ifamp.htm

https://www.daenotes.com/electronics/communication-system/superheterodyne-fm-receiver

https://www.electronics-notes.com/articles/radio/superheterodyne-receiver/theory-principles.php

https://www.diffen.com

https://www.daenotes.com