1. INTRODUCTION
FM Ratio Receiver Project Report. The FM Band transmission has started very
recently in India but its superior technique and quality has attracted the listeners.
Unlike AM, the FM is a separate band and its frequency ranges from 88MHz to 108
MHz. The FM Band can not be received by the conventional AM receivers. Each and
every AM receiver does not incorporate FM facility. The present project is a very low
cost project and it can be fitted to any radio receiver/audio system to receive FM
transmission. The circuit of this project is very simple and can be easily assembled.
Antenna
A theoretical study of radiation from a linear antenna (length l)
Power radiated a (p/l)2
This implies that for the same antenna length, the power radiated by short wavelength
or high frequency signal would be large. Hence the effective power radiated by long
wavelength base band signal would be small for a good transmission, we need high
power hence, this also point out to be need of using high frequency transmission.
Modulation
In amplitude modulated communication, propagation of radio waves from the
transmitting antenna to the receiving antenna takes place in the following two
important ways :
1. Ground Wave Propagation
2. Sky Wave Propagation.
The transmitted radio waves are supported at their lower edge by the ground. The
radio waves have to be vertically polarized, so as to prevent the short circuiting of the
electric field component of the wave. The radio wave induces current in the ground,
over which it passes. It attenuates to some extent due to partial energy absorption by
the ground.
Types of modulations
1. Amplitude Modulation :
In the frequency range 500 kHz. to 30 MHz, amplitude modulation of the signal is
employed and accordingly this frequency range is termed as amplitude modulated
2. band (AM bond). The earth’s atmosphere is more or less transparent to the
electromagnetic waves in AM band. However, the ionosphere (the topmost layer of
the atmosphere) does not allow the electromagnetic waves in AM band to penetrate it
and they are reflected back. When the frequency of electromagnetic waves is above 40
MHz, they are no longer reflected by the ionosphere but undergo refraction. Keeping
the above facts in view, the amplitude modulated signal in medium wave frequency
range (up to 1500 kHz.) is transmitted by surface wave propagation or also called
ground wave propagation. In the short wave frequency range (from a few MHz to 30
MHz), the amplitude modulated signal is transmitted via reflection from the
ionosphere. It is called sky wave propagation.
2. Frequency Modulation :
For frequencies of electromagnetic waves above 40 MHz, frequency modulation of
the signal is preferred. In the transmission of TV signals, the frequencies of the
electromagnetic waves waves employed ranges from 30 MHz to 1000 MHz. The
transmission of electromagnetic waves in this frequency range can neither be made by
surface wave propagation nor by sky wave propagation. The surface wave
propagation is not possible for the reason that the ionosphere cannot reflect the
electromagnetic waves in this frequency range. Further, in the frequency range 30 cm.
to 10 m. FM transmission are made from small antennas.
Advantages
Now-a-days there is a necessity of FM projects in the electronic market. Through this
project different FM stations can be tuned but in India. Presently there is one FM
channel. As such the project is designed for one channel to avoid possible damage of
the coil in tuning again and again. The FM transmission is stereo phonic. As such you
can connect it to any stereo deck and enjoy the stereo sound. Now a days two-in-one
and radios with FM band are available in the market. But without replacing your old
radio set you can connect this project to your old radio/two-in-one and enjoy the FM
transmission. It is quite economical too. Unlike AM receivers, the FM receiver is
assembled through different stages.
(i) FM Amplifier
(ii) Mixer
(iii) Oscillator
(iv) AGC
3. (v) Discriminator (Detector)
(vi) Audio Pre-Amplifier.
Integrated circuit
All the functions are performed by the IC-5591 which is employed in the circuit. The
audio signal available from the preamplifier is fed to audio output amplifier for further
amplification. The RF of FM band transmission is fed to pin no. 2 of the IC TA5591
through the aerial, which also works for FM amplifier, oscillator and mixer stage. A
ceramic filter of 10.7 MHz. is connected to the local oscillator pin no. 4, 5 and 6 of
IC. A 9 volt DC supply is fed to pin no. 8 of the IC. Pin no. 10 of the IC is
discriminator pin. The audio signal is available from pin no. 11 of the IC. Pin no. 18,
19 and 20 of the IC are IF amplifier pins while pin no. 22 and 24 are local oscillator
pin. Two trimmers are connected to the circuit. The range of the frequency can be
varied by rotating the trimmers. A gang condenser equivalent to the value of the
trimmer can also be used in place of trimmer if available. This project can operate in
the range of 3V to 12 Volt DC supply. However the trimmers are to be adjusted to get
best reception.
Apparatus required
S.No. Part Qty.
1. IC-5591 1
2. Ceramic Filter 10 MHz. 2
3. Resistance 56 E 1
4. Capacitor 470 PF 1
5. Capacitor 22 PF 4
6. Capacitor .022 3
7. 4.7 MFD/63 V. 2
8. One Pole two way switch 1
4. FM RADIO RECEIVER CIRCUIT
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This simple fm radio receiver circuit consists of a regenerative rf stage, TR1, followed by a
two of three-stage audio amplifier, TR2 to TR4. In some areas 3 stages of audio
amplification may not be necessary, in which case TR3 and its associated components can
be omitted and the free end of capacitor C5 connected to the collector of TR2.
The critical part of the fm radio receiver is the first stage, TR1/VC1, where the wirings must
be kept as short as possible. Coil L1 is formed by winding 8 turns of 1mm (20 swg)
enamelled copper wire on a 6 mm diameter former, which is then removed. After that L1
should be stretched carefully and evenly to a length of about 13mm.
FM Radio Circuit Diagram
Transistors List
5. TR1 = BF199
TR2 = TR3 = TR4 = BC547
Video presentation and photos of the working receiver
byAleksandar
The tunning capacitor VC1 is one of the two fm sections of a miniature fm transistor radio
with built-in trimmers (VC2). The “earthy” end (moving vanes and spindle) is connected to
the 22pF capacitor C1. The value of the rf choke L2 is not critical, anything from 1µH to
10µH being suitable.
The output is suitable for ordinary earphones connected in series to provide an impedance
of 64Ω.
Tuning-in the fm radio receiver
To operate the receiver, potentiometer VR1 must first be advanced slowly (towards the end
of the track connected to battery positive) until, at about the half-way point, a sudden slight
increase in background noise will be heard, indicating the onset of oscillation. It then should
6. be backed off, very slowly, until oscillation just stops; it then should be possible to tune in
some stations.
The correct frequency range of 87 MHz to 108 MHz can be obtained by adjusting VC2 at the
high frequency (108 MHz) and slightly stretching or squeezing together the turns of coil L1
at the end (87 MHz).
7. Build A One Transistor FM Radio
updated designs!
See below for: Click here for:
My new, improved The new, improved
One Transistor FM Radio Radio Shack Special FM Radio
or
Build
Build this one transistor
this one transistor FM radio
FM radio
(my design)
(Designed by Patrick Cambre)
8. Enlarge: [large]
Enlarge: [medium] [large] See the new improved version on Patrick's web
site
My Design
A printed circuit board for the original circuit is available through FAR Circuits. Ask
them for "Andy Mitz'sOne transistor FM radio printed circuit board". The same
circuit board can be modified for the improved one transistor radio.
Introduction
AM radio circuits and kits abound. Some work quite well. But, look around and you
will find virtually no FM radio kits. Certainly, there are no simple FM radio kits. The
simple FM radio circuit got lost during the transition from vacuum tubes to
transistors. In the late 1950s and early 1960s there were several construction articles
on building a simple superregenerative FM radio. After exhaustive research into the
early articles and some key assistance from a modern day guru in regenerative circuit
design, I have developed this simple radio kit. It is a remarkable circuit. It is
sensitive, selective, and has enough audio drive for an earphone. Read more about
theory behind this radio on the low-tech FM page.
9. Construction
parts source
Except the the circuit board and battery, all parts are from Mouser Electronics. A
complete parts list with stock numbers is listed below. The circuit board is available
through FAR Circuits. The variable capacitor is available through Electronix Express.
layout
Because this is a superregenerative design, component layout can be very important.
The tuning capacitor, C3, has three leads. Only the outer two leads are used; the
middle lead of C3 is not connected. Arrange L1 fairly close to C3, but keep it away
from where your hand will be. If your hand is too close to L1 while you tune the
radio, it will make tuning very difficult.
winding L1
L1 sets the frequency of the radio, acts as the antenna, and is the primary adjustment
for super-regeneration. Although it has many important jobs, it is easy to construct.
Get any cylindrical object that is just under 1/2 inch (13 mm) in diameter. I used a
thick pencil from my son's grade school class, but a magic marker or large drill bit
work just fine. #20 bare solid wire works the best, but any wire that holds its shape
will do. Wind 6 turns tightly, side-by-side, on the cylinder, then slip the wire off.
Spread the windings apart from each other so the whole coil is just under an inch (2.5
cm) long. Find the midpoint and solder a small wire for C2 there. Mount the ends of
the wire on your circuit board keeping some clearance between the coil and the circuit
board.
a tuning knob for C3
C3 does not come with a knob and I have not found a source. A knob is important to
keep your hand away from the capacitor and coil when you tune in stations. The
solution is to use a #4 nylon screw. Twist the nylon screw into the threads of the C3
tuning handle. The #4 screw is the wrong thread pitch and will jam (bind) in the
threads. This is what you want to happen. Tighten the screw just enough so it stays
put as you tune the capacitor. The resulting arrangement works quite well.
Adjustment
If the radio is wired correctly, there are three possible things you can hear when you
turn it on: 1) a radio station, 2) a rushing noise, 3) a squeal, and 4) nothing. If you
10. got a radio station, you are in good shape. Use another FM radio to see where you are
on the FM band. You can change the tuning range of C3 by squeezing L1 or change
C1. If you hear a rushing noise, you will probably be able to tune in a station. Try the
tuning control and see what you get. If you hear a squeal or hear nothing, then the
circuit is oscillating too little or too much. Try spreading or compressing L1. Double
check your connections. If you don't make any progress, then you need to change
R4. Replace R4 with a 20K or larger potentiometer (up to 50K). A trimmer
potentiometer is best. Adjust R4 until you can reliably tune in stations. Once the
circuit is working, you can remove the potentiometer, measure its value, and replace it
with a fixed resistor. Some people might want to build the set from the start with a
trimmer potentiometer in place (e.g., Mouser 569-72PM-25K).
Substituting other components
Many of the parts are fairly common and might already be in your junk box. Only
certain component values are critical. The RF choke should be in the range of 20 to
30 uh, although values from15 to 40 uh might work. The tuning capacitor value is not
critical, but if you use values below 50 pf you should reduce or remove C1. The
circuit is designed for the high impedance type earphone. Normal earphones can be
used, but the battery drain is much greater and the circuit must be changed. To use
normal earphones, change R3 to 180 ohms. Q1 can be replace with any high-
frequency N-channel JFET transistor, but only the 2N4416, 2N4416A, and J310 have
been tested. A MPF102 probably will work. C2 is not too critical; any value from 18
to 27 pf will work. C7 is fairly critical. You can use a .005 or .0047 uf, but don't
change it much more than that.
Improved design for more audio gain
Chris Iwata recommended some design changes that greatly improve the audio circuit,
making it strong enough for regular earphones or even a small speaker. The same
FAR printed circuit board can be used with some modifications. The circuit board is
important to make sure the tuning end of the radio works properly, so the audio
amplifier changes can be squeezed onto the circuit board without fear of wrecking
radio operation. Look closely at the new schematic for the new components and some
changed component values.
Schematic diagram for the Original One Transistor FM Radio
Click here for a PDF version of the schematic. You can also make this into a simple
CB radio receiver. See this PDF file.
11. Schematic diagram for the One Transistor FM Radio with Improved Audio Gain
Click here for a PDF version of the schematic.
12. One Transistor FM Radio with improved audio gain.
Printed circuit board
The printed circuit board for the original One Transistor FM Radio is available
through:
13. FAR CIRCUITS
Printed Circuit Boards
18N640 Field Court
Dundee, Illinois 60118
(847) 836-9148 Voice/Fax
email: farcir@ais.net
Some wiring notes:
Unless you have experience with super-regenerative radios, I highly
recommend using the FAR Circuits printed circuit board.
Connect the two sections of the variable capacitor (C3) in series to linearize the
tuning somewhat. That is, use the connections on either end of C3 and don't
use the middle lead.
L2, the RF choke should not be near a ground. The same is true for L1.
Capacitance to ground will disturb the feedback.
The gain is just enough to drive an earphone. If you live too far away from
radio stations, you might have trouble hearing one. There is no option here for
an external antenna (that would require and extra transistor).
You can drive a speaker if you add an external audio amplifier.
If you want a little more audio gain, or you cannot locate a TL431CLP chip,
you can use some other audio amplifier in the circuit where pins 1 and 2 of D1
normally connect. You can use an LM386 or a TDA7052 audio
amplifier. Quasar DIY project kit #3027 is a complete TDA7052 audio
amplifier kit and it works fine in this application.
Parts list for original circuit (see schematic of the improved version for new part values)
All parts except the RF tuning capacitor can be obtained from
Mouser Electronics
www.mouser.com
sales@mouser.com
1-800-346-6873
The RF tuning capacitor can be obtained from
Electronix Express
electron@elexp.com
15. S1 Small SPST switch 10SP003
screws for mounting C3 (2
screws for C3 48SS03
needed)
nylon screw #4 nylon screw used for tuning C3 561-T0440037
battery connector mini battery snap 12BC025
16. How to build a very simple FM/AM Receiver using
TDA7088 ?
I was browsing the Philips website when I came to this IC : TDA7088 and I said wow , it was the
simplest AM/FM radio I ever saw. I looked on its price on a local electronic parts provider and it was
about 5 RON (~1.7$) so it is worth building this radio as a hobby project.
Features of the chip :
Equipped with all stages of a mono receiver from antenna to audio output
Mute circuit
Search tuning with a single varicap diode
Mechanical tuning with integrating AFC
AM application supported
Power supply polarity protection
Power supply voltage down to 1.8 V.
A simple circuit, taken from the application notes :
17. As we can see it doesn’t have an audio amplifier so you must build one for it! After another search I
found an extremly simple and low cost (~1.2$) AA done with TDA7050 :
After my exams I think will do it and put here the construction images .
