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 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

(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

FM RADIO RECEIVER CIRCUITPosted by P. Marian in Radio | 44 comments

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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 ListTR1 = BF199TR2 = TR3 = TR4 = BC547

Video presentation and photos of the working receiver

by Aleksandar

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 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).

Build A One Transistor FM Radioupdated designs!

See below for:

My new, improvedOne Transistor FM Radio

Click here for:

The new, improved   Radio Shack Special FM Radio

Build

this one transistor FM radio(my design)

or

     Build this one transistor FM radio

(Designed by Patrick Cambre)

 Enlarge:  [medium]  [large]

 Enlarge: [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's One 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 .

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

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.

 

 

Schematic diagram for the One Transistor FM Radio with Improved Audio Gain

Click here for a PDF version of the schematic.    

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:

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 fromMouser Electronicswww.mouser.com sales@mouser.com1-800-346-6873

The RF tuning capacitor can be obtained fromElectronix Expresselectron@elexp.com1-800-972-2225In New Jersey 1-732-381-8020

Part designator Part description Vendor stock number

C1a,C1b 10 pf, 50 v, ceramic disc capacitor 140-50N5-100J

C2 22 pf, 50 v, ceramic disc capacitor 140-50N5-220J

C3 RF tuning capacitor N14VCRF10-280P

C4 330 pf, 50 v, ceramic disc capacitor 140-50P2-331K

C5,C80.001 uf, 50 v, ceramic disc capacitor

140-50P2-102K

C6 0.22 uf, 50 v, film capacitor 140-PF1H224K

C70.0047 uf, 50 v, ceramic disc capacitor

140-50P5-472K

C9 22 uf, 16 v, electrolytic capacitor 140-XRL16V22

D1TL431AIZ voltage control Zener (shunt regulator)

511-TL431AIZ

EPH1 High impedance earphone 25CR060

L2 22 uh RF choke 542-70F225

Q1 2N4416A JFET transistor 510-2N4416A

R1 470K, 1/4 w, resistor 291-470K

R2, R3 1K, 1/4 w, resistor 291-1K

R4 10K, 1/4 w, resistor 291-10K

R5 1M, 1/4 w, resistor 291-1M

R6 100 ohm, 1/4 w, resistor 291-100

S1 Small SPST switch 10SP003

screws for C3 screws for mounting C3 (2 needed) 48SS03

nylon screw #4 nylon screw used for tuning C3 561-T0440037

battery connector mini battery snap 12BC025

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 :

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   .

Bibliography:

http://www.semiconductors.philips.com/pip/TDA7088.html  – reference page for TDA7088

http://www.semiconductors.philips.com/pip/TDA7050.html  – reference page for TDA7050

TDA7050 DatasheetDownloads: 4075 File Size: 0.0 KB File Name: TDA7050_CNV_2.pdf

TDA7088 Datasheet