mini fm station_1

8/6/2019 Mini Fm Station_1

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CHAPTER-1

1. Introduction

1.1 Term paper overview:

The aim of term paper is to transmit voice or audio wirelessly from one place

to another place in the FM band (88-108MHz). For generation of voice and audio

frequency modulation techniques are used. The instantaneous frequency fi(t) is varied

linearly with the message signal (voice or audio signals) variation.

The variations of amplitude of message signal causes changes in frequency of

carrier wave linearly. So the carrier carries the message signal in the form of

frequency variations. The frequency modulated wave produced by the circuit is

converted in to electromagnet radiation for the transmission of the voice or audio into

free space. The job of converting frequency variations of electrical signal into

electromagnet waves is achieved by an antenna.

The antenna can be telescopic antenna or simply a wire antenna. The time harmonic

electrical variations of the FM wave are converted to electromagnetic radiations by

the antenna and are transmitted into free space. Now the voice or audio information is

in the form of electromagnetic radiations in the free space.

To reproduce the voice or audio signal at the receiver, first of all we must capture

the EM waves, convert them to electrical FM waves. And then demodulate those

signals back in to voice or audio signals. Thus voice or audio is transmitted and


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received wirelessly over a range. The range can be improved by selecting proper

antenna wire antenna works well but covers a short range distance.[1]

The receiver used here is a general purpose FM receiver (FM radio). Is

commercially available at cheaper costs in the market without need of designing it

again. So in order to transmit signal we must have a transmitter circuit which can

transmit the voice or audio in the readily available FM receiver (FM radio) band of

(88-108MHz). We also require a voice and audio modules to voice and audio signals

and an audio amplifier to amplify those signals.

Frequency modulation is as shown in the Fig 1.1 [9], Fig 1.2:


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Fi 1.1 M l di of frequency modul tion


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Fi 1.2 Block di ram

1.2 FM generati n

General FM wave equati n i :

S(t ) = Ac cos{2fi{t}t +}(1.1)

fi(t) = fc+ k fm(t)(1.

FM waves[1] can be generated by 2 basic met ods namely direct met od and

indirect met od. In t e indirect met od of producing FM waves t e modulating wave

is first used to produce narrow band FM wave, and frequency multiplication is done

to increase t e frequency deviation to required level.The frequency multiplication is

done with the help of a non-linear device operated in non-linear region deliberately to

get harmonics and hence frequency multiplication is achieved.

On the other hand in the direct method of generation of FM waves, the carrier

frequency is varied directly in accordance with the message signal(voice or audio).

Here we go with direct method as it is simple and can be achieved with few

components, without going to the complex indirect method.


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Direct method of generation of FM signal requires a voltage-controlled oscillator

to vary frequency of carrier with the message. The one to implement such a device is

sinusoidal oscillator having relatively high Quality factor frequency determining

network and to control the oscillator by incremental variation of the reactive

components.

Here what oscillator should be used is the question now? Suppose that it is an RC-

phase shift oscillator, but it is not possible to get such a high frequencies (100MHz)

with that RC oscillator, it is limited to produce up to audio frequency range only. So

we have two more choices LC (Colpitts or Hartley) or CRYSTAL oscillator, the

circuit presented here uses LC oscillator preferably colpitts oscillator.

Colpitts oscillator is selected here instead of Hartley oscillator this is from the fact

that Hartley oscillator uses two inductor coils and they again have mutual inductances

which are complex and give unknown practical variations of frequencies. And other

reason is that if we imperfectly wind the coil, the imperfection is doubled using two

coils in the circuit and the small variations in the inductance values causes large drift

in the frequencies. For all the above reasons colpitts oscillator is preferred.

1.3 Working

The two modules voice module and audio modules give voice signal and audio

signal respectively as their outputs. In voice module microphone transducer catches

voice signal, the op-amp pre-amplifies the voice signal, which is given to amplifier.

The audio module does not have any special circuitry, it is the output taken

from the cell phone head-phones socket. The output taken from cell phone is


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amplified by amplifier unit. The amplifier is switched between voice and audio

modules i.e., only of the them can be connected at a time.

The output of amplifier is an amplified version of either voice or audio. So

now we are with an audio or voice signal from amplifier at hand which is to be

wirelessly transmitted over a distance the amplifier output is connected to the FM

transmitter input.

FM transmitter circuit also consists of two complementary transistors which

amplify the signal to the required level demanded by the oscillator section of the

transmitter. The amplified output fed to the oscillator can be adjusted by the preset for

the clarity in the receiver.

The transmitter circuit consists of oscillator unit, the oscillator when supplied

with power oscillates with constant frequency, but constant oscillations doesnt have

any information of transmitted voice or audio, so we must somehow vary the

frequency linearly with the amplitude level changes of the voice or audio.

The following is one of the several ways i.e., here base-emitter junction

capacitance is varied according to applied signal amplitude .the variation of

capacitance causes frequency variations. Hence forming voltage controlled

oscillator, this VCO can also be formed with the help ofvaricap (bb109), but varicap

not used here.

The frequency variations are again converted to amplitude variations at

demodulator (receiver side), with the help of phase locked loop. The output produced

from the Common Emitter amplifier is 180 degrees out of phase that is -Vi

(amplified). The phase shifted signal reverse biases the base-emitter junction of the

2N2219 transistor.


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When the voice or audio signal reverse biases the base-emitterjunction the

width of the depletion region changes more is the reverse bias voltage of audio or

voice signal more is the width of the depletion region. That is the immobile charges

are separated by more distance when more reverse bias voltage of voice or audio is

applied.

The positive and negative immobile charges separated by a distance and with

electric field between them gives capacitive action to the base emitterjunction. If

reverse bias is more, the distance of charges separated by electric field is more and

vice-versa and if distance of charge separation is more then the capacitance is less.

This is obvious from the eq (1.3.1).[14][2][3]

Fig 1.3: Base emitterjunction Fig 1.4: Base emitterjunction

Fig 1.5 Depletion region of base-emitterjunction


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C = oA/d ..(1.3)

Where c is the capacitance

o is the permittivity

A is the area of electric field

d is the width of depletion region in this context.

So as d increases with reverse bias voltage the capacitance decreases and as d

decreases the capacitance increases. In this way the capacitance of base-emitter

junction varies with varying voice or audio signal.

As the capacitance of the base-emitter junction varies, the frequency of

oscillations of the oscillator changes according to the applied bias voltage (voice or

audio). Hence the message to be transmitted is frequency modulated. The modulated

signal is transmitted in to free space by an antenna. The transmitted signal is received

by the FM receiver where the transmitted signal is reproduced back.


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CHAPTE 2

2.1 Voi e module:

The voice module will do the job of converting our voice signal in to an

amplified electrical signal which is given as inputto FMtransmitter circuit, which is

to be transmitted to free space.

2.1.1 Mi rophone:

The circuit uses a condenser mic or ECM as transducer for converting sound

signalto electric signal [12].

Fig 2.1 Microphone.


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An ECM contains a very sensitive electret

type microphone (high output impedance) and an

integral FET amplifier. The amplifier stage buffers

the high output impedance of the microphone and

boosts an average speech signal to around 1 to

2mV when spoken about 1 meter away from the

microphone. The ground or common connection of

a two terminal ECM insert can be identified is the

solder connection thatis touching the case or body

ofthe microphone.[16] Fig 2.2 Circuitto bias ECM

The ECM microphone passive component (capacitive transducer) it cannot

give away output voice without powering it .so proper biasing must be employed in

orderto make it work. The biasing is done as follows; the signal output is connected

to the powerterminal, fed via a currentlimiting resistor, (typical value 1k or 2k). The

signal output therefore has a DC component (signal clamped to a dc value) which

must be removed.

Before connecting to an amplifier, this is achieved with an output capacitor

connected to the power terminal ofthe ECM, as capacitor blocks or open circuit for

dc component, only alternating component is passed to input of pre-amplifier. A

typical value being 1-10uF would serve the purpose.

When the circuit is connected as shown in the Fig 2.2, we can obtain our

speech variations converted as electrical signal (with almost no dc component). But


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the output we get from here is an order of few mill volts (1-2mV). So it must be pre-

amplified. Forthis purpose the pre-amplifier circuitis employed here.

2.1.2 Mi rophone pre-ampli ier:

The Fig 2.3 is a high quality microphone preamplifier using a single power

supply, suitable for dynamic or electret microphones. The op-amp used can be any

low noise, high performance type, e.g. NE5534, TL071, OPA 371 etc.

Already we are able to bias the microphone and getlow output (1-2mV), this output

voltage is connected to the input of pre-amplifier circuit.[15] Circuitdiagram:

Fig 2.3 Circuit diagram of microphone pre- amplifier

2.1.3 Circuit description:


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The design is op-amp connected in a standard non-inverting configuration

The overall voltage gain is determined by R2 and R1according to the following

formula:(assuming vi=1mV from microphone)

Vo = (R2 / R1) +1 (2.1)

The input is applied to the non-inverting input of the op-amp, which is pin3.

The amplified output is collected from pin 6, a capacitor is used here to blockD.C and

to take only alternating components output. A 100 microfarad capacitor is used here

to remove unwanted ripple.

2.1.4 Op-amp description

TL071[19] is high speed low noise J-FET input single operational amplifier

incorporated well matched high voltage J-FET and bipolar transistors in a monolithic

integrated circuit.

2.1.5 Specifications:

y High slew rates 16v/u sec

y Low input bias and offset currentsy Low offset voltage temperature coefficient

y Wide common mode and differential voltage range

y Low noisey Low harmonic distortion 0.01%(typical)


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y Internal frequency compensation

y Low latch up problem.

y With the values ofR2 and R1 on the diagram the voltage gain (for mid band, 1KHz) is approximately 23x or 27.2dB The gain bandwidth (bode) plot is

shown in Fig 2.4. This plotis simulated using the TL071 op-amplifier.

Fig 2.4 Graphs

Operational amplifiers feature high gain bandwidth products, have a fast

slewing rate and have extremely low noise. It is difficult to achieve the same

performance using discrete components. Finally the overall signal to noise ratio has


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been calculated, the source was a 1k impedance microphone generating a 1mV (p-p)

sine wave.

2.1.6 Pin diagram ofTL 71

Fig 2.5 Pin diagram of TL071

The output from this pre-amplifier [16] is enough to drive a headphone. Butto

apply this as an input fortransmitteris not enough. So, the pre-amplifier output must

be applied to an audio amplifier, to feed it as inputto transmitter. Before feeding itto

audio amplifier input it can be tested with the hel p of headphones or small (low

resistance) loudspeaker. The loud speaker gives a small sound which ensures us that

signal from microphone is being amplified.

2.2 Audio module:

Devices which can give out audio output such as tape-recorders, DVD players,

I-pods or even a cell phone can be used here in the module. This module is very

simple as audio signalis directly available and ourjob isjustto amplify it by an audio


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amplifier. Butthe question here is how to connect audio device to amplifier section-1

to do this we must use a male socket is employed which must be connected to

headphones output of cell phone. Audio device selected here is cell phone.

2.2.1 Male socket:

The male socketis as shown in the Fig 2.6

Fig 2.6 Male socket

The wires are soldered to the male-socket [13] inside the plastic covering and

audio output is collected using connecting wires. The connecting wires are then

connected to the input of audio amplifier. And the audio amplifier amplifies the song

or music given out by the cell phone. This module can also be tested using

loudspeaker to the amplifier. By adjusting the potentiometer proper sound is heard

loud. The loud speaker used forthis purpose can be a 8 Ohm or 4 Ohm (5W).


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CHAPTER-3

3. Amplifier:

The audio amplifier [13] mainly consists of IC LM386. LM 386 is a general

purpose audio amplifier IC. The circuit consists of the IC LM386 and some external

passive components. A 1 F capacitor is used to couple amplifier unit to block from

any dc entering in to the cell phone through male socket.

3.1 Features

Battery operation

Minimum external parts

Wide supply voltage range: 4V-12V or 5V-18V

Low quiescent current drain: 4mA

Voltage gains from 20 to 200

Ground referenced input

Self-centering output quiescent voltage

Low distortion: 0.2% (AV = 20, VS = 6V, RL = 8Ohm, PO = 125mW, f = 1kHz)

Available in 8 pin MSOP package

3.2 Description

The LM386 is a power amplifier designed for use in low voltage consumer

applications. The gain is internally set to 20 to keep external part count low, but the

addition of an external resistor and capacitor between pins 1 and 8 will increase the

gain to any value from 20 to 200. The gain can be varied by connection. The inputs

are ground referenced while the output automatically biases to one-half the supply


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voltage. The quiescent power drain is only 24 mW when operating from a 6 volt

supply, making the LM386 ideal for battery operation.

3.3 Applications

AM-FM radio amplifiers

TV sound systems

Line drivers

Ultrasonic drivers

Note: To make the LM 386 [19] a more versatile amplifier, 2 pins (pin 1 and 8) are

provided for gain control. With pins 1 and 8 open the internal 1.35k resistor sets the

gain at 20 (26 dB). If a capacitor is placed between pin 1-8, bypassing the built-in

1.35k resistor, the gain will go up to 200. If a resistor is placed in series with the

capacitor, the gain can be set to any value from 20 to 200. Gain control can also be

done by capacitively coupling a resistor or FET transistor from pin 1 to the ground.

3.4 Pin diagram ofLM386

Fig 3.1 Pin configuration of LM386


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Fig 3.2 LM386 Audio Amplifier with Gain = 20 and minimum part count

Fig 3.3 LM386 Audio Amplifier with Gain = 200

Fig 3.4 Audio Amplifier with bass boost


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Fig 3.5 Pictorial view of LM386 amplifier

The output of amplifieris connected to the transmitterinput, by that we are feeding

message signalto be transmitted to the transmitter circuit.


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CHAPTE -4

4. FM Transmitter section:

FM transmitter section [7] uses simple circuit which is as shown in the Fig 4.1.

Circuit basically consists of a pre-amplifier and an oscillator.

Fig 4.1: FMtransmitter circuit diagram

The input of FM transmitter is having a 10k (R2) resistor which attenuates

the incoming signal from the amplifier. The 0.033F capacitor(C2) removesthe D.C


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level that is taken from the amplifier (capacitor blocks d.c) hence only alternating

componentis feed as inputto the transmitterinput .

Transmitter also contains pre-amplifier section which amplifies the signal to

desired levelthatis exactly needed for oscillator section. A doubt may be arising what

is reason behind using a pre-amplifier in this section also, as it is used before. The

reason for this is, the input to transmitter is not enough to modulate the oscillator

section. And other obvious reason is to isolate the transmitter and voice or audio

modules.

4.1 Pre-amplifier stage:

The resistor values 27K(R4) and 120K(R2) provide biasing for transistor

BC109.The biasing scheme employed here is a voltage divider bias. The capacitor

15F (C1) can be assumed as short circuit for a.c analysis. The base-collector

junction is reversed biased (this is eitherit may be npn or pnp).The signalis amplified

by BC109 (Q1), [19]which is a low noise npn type transistor. The 470 Ohm resistor

(R8) drops some voltage such that entire voltage is not applied directly to the

transistors.

4.1.1 BC109

Fig 4.2 Pictorial veiw of BC109


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Features:

Low current (100mA).

Low voltage (45V).

Applications:

General purpose switching and amplification.

The 47F capacitor (C4) used here is to bypass unwanted ripple or

oscillations. A 10 (R6) resistor is used to collect output and feed this to next stage.

1 resistor (R3) emitter resistor stabilizes the Q-POINT of the transistor. The

general and simple terminal convention applicable to almost all germanium (metal

case) transistors orBC109 and BC177 for instance is that the terminal near the notch

will be emitter, middle one is base and other is collector.

The output of transistor Q1 is connected to the input of the transistor Q2

(BC177 pnp transistor). The transistors BC109 and BC177[19] are complement to

each other, i.e., they have almost same beta value and BC109 is npn and BC177 is

npn. (can be used in complementary symmetry pair in push-pull amplifiers). Similar

to Q1, the transistor Q2 should have reverse biased base-collector junction and

forward biased base-emitter junction, Such that the transistor is in active region and

amplifies the signal.

To maintain the base-collector junction in reverse bias condition the emitter is

connected to Vcc and collector to ground such that the collector of the pnp transistor

(p-type) is connected to ground and base(n-type) is positive with respect to ground

and hence the transistors base-collector junction is reverse biased and in the similar


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way emitter(p-type) is positive with respectto base and is maintained in forward bias,

eventually the transistoris in active region and can amplify the signal at hand.

4.1.2 BC177 (Q2):

BC177 transistoris a low noise general purpose amplifier.

It is an pnp type transistor which is known to be complement transistor for BC109

whose beta values range is almost same, so they both are used as pairin the circuit.

The resistor (R5) 100 Ohm is connected to emitter to stabilize the Q-POINT. The

output is again collected from the collector only but this time using a4.7K preset

(R9) or potentiometer (can be used).

Fig 4.3 Potentiometer Fig 4.3 Preset


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Preset is best here because it is very small and cheaper than a potentiometer. The

preset is adjusted for clarity of received voice or music. 4 Resistor (R ) and capacitor

0.022F (C3) form a feedback network, this feedback network increases bandwidth and

decreases the noise. And againcapacitor (C5) 0.4 F

couples only a.c and blocks d.c.

Hence only time varying component is allowed to oscillator stage. Transistor2N2219 (Q3) is

a power amplifier.

4.1.3 Transistor 2N2219 (Q3):

2N 2219[19] is a power amplifier is of n-p-n type.

Features

High current (Max. 800 mA)

Low voltage (Max. 40 V).

Applications

High-speed switching

DC and VHF/UHF amplification, for 2N2219 only.

PIN DESCRIPTION

1 Emitter

2 Base

3 collector, connected to case

Table 4.1 Pinning


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Table 4.2 Quick reference data

Note: The base emitter junction capacitance of 2N2219 transistor is 25pF max from the

data sheet.

4.2 Oscillator section

The section to be described is an oscillator section.2N2219 forms oscillator, from the

Fig 4.4 does it seem to be an oscillator? Rearranging the above circuit and carrying out A.C and

D.C analysis separately the overall effect of both at a time can be analyzed.


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Fig 4.4 Separate oscillator section

A.C analysis

1.The capacitor bypasses for a.c and offers very low reactance value.[3],[5]

D.C analysis:

1. Capacitors replaced by open circuit.

2. Inductor is replaced by shot circuit. From the a.c analysis it is clear that the circuit is a

colpitts oscillator. From d.c analysis it is evident that the resistances present are for the biasing

of the colpitts oscillator. From a.c and d.c analysis we come to a conclusion that the circuit is a

biased colpitts oscillator.

The resistor 56 ohms (R12) stabilize the Q-point.[18]


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V -220j RF Choke

VK-220j is a radio frequency choke, it blocks high frequency components and allows low

frequency components. The purpose of using this choke here in this circuit is to block

oscillations of high frequency from oscillator section to pre-amplifier section. ForD.C it behaves

as short circuit and hence it freely allows Vcc d.c component (supply) with no attenuation. For

high frequency oscillations it blocks and does not allow oscillations to go through it.

VK-220j does not allow oscillations to get in to pre-amplifier section so carrier hum is

eliminated as reverse is minimum by using this choke the power loss in the circuit itself is

minimum, this increases the range of the transmitter. The choke provides isolation between pre-

amplifier and oscillator so the received signal will have clarity without unwanted disturbance.

The choke can be replaced by a solenoid wound on a ferrite bead, as VK-220j is not so readily

available in the market and it is always cheap and best way to make it ourselves. Wound 8 turns

of24 SWG wire on a ferrite bead, ferrite bead increases magnetic flux and acts as a good

choke.

Variable capacitors:

Two trimmers[12] can be used as the variable capacitors C9 (45pF)&C8(15pF). The

capacitance range of trimmer is 5pF to 45pF.

Fig 4.5 Trimmer


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The capacitance can be varied by using a screw-driver(screw is rotated to change

capacitance).The middle lead is one of the terminal to be connected the other terminal can be

left one or right one, the left and right leads are the wipers to select the desired capacitance

value. Also do not vary the capacitance by hand, using hand damps the oscillations as hand

contributes to some capacitance, the oscillations are grounded. After each adjustment the

screw-driver must be removed. Patience is required in tuning the trimmer to select desired

station.

Inductor(L1)

The pre-assumed dimensions solenoid is wound and is used as inductor.[12]

Fig 4.6: Solenoid

Number of turns (N) = 4

Radius of the coil(R) = D/2=12/2=6mm

Wire diameter = 24SWG =0.5588(from SWG to mm conversion table)

The length of the coil (L) =2.5mm.


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Table 4.3 SWG to mm conversion

The inductor[9] calculations are done with the help of a software called RFCALC,

RFCALC has three choices .First choice is unknown air coil inductance is selected, the snap of

the RFCALC is shown in Fig 4.7.

Fig 4.7 RFCALC window


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4.3 Antenna:

The antenna used here can be a telescopic antenna or simply a wire with length of

75cms.If the length exceeds 1metre the oscillations get damped and no signal is transmitted,

the length is chosen as quarter wave monopole i.e., / 4 (75cms), this is proved in the

following calculation

= C / f ..(4.1)

Where C is velocity of light (or any electromagnetic radiation) = 3 x 10^8 mts / sec

is wavelength of EM wave(unknown)

f is the frequency of carrier signal(100MHz)

Substituting the above values, we get

= 3 x 108 / 100 x 106=3 mts.

Taking quarter wave monopole ( / 4) = mts =75cms.

Hence 75cm wire can serve purpose of an antenna.[1]


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CHAPTER-5

5.1 Precautions (based on practical observations):

y Do not touch the oscillator section with hands, because due to hand capacitance(apprx.220pF), the oscillations are damped (transistor or trimmers).[7][8]

y Assemble the circuit on good quality glass epoxy board.y Better to enclose the circuit in the aluminium case, so that the unwanted disturbance sounds

can be avoided.

y ForHUM FREE (a.c supply hum) operation 12V rechargeable battery pack10x1.2VNI-CD cells.

y Do not SWITCH-ON the transmitter without matching antenna, this causes heat sink togenerate large amount of heat (transistor gets heated).

y Care must be taken such that the leads of the components are as short as possible, this,which gives clarity of signal, received at the receiver.

y After each adjustment of the trimmer check for the clarity because, while the trimmer isbeing adjusted the oscillations get damped.

y The receiver and transmittermust not be very close, this creates cracking sounds.y The transmitter section and amplifier sections must be properly isolated, if not the oscillations

enter the amplifier module and create nuisance effect.

y The antenna length is a quarter wave monopole length i.e 75cms, if wire length exceeds1mt the oscillations will not be transmitted and are damped at transmitter end itself.


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y The antenna must be having good matching characteristics for good signal strengthy The impedance match can be obtained by winding another coil with 2turns near the L1 on the

same plastic former.

y Yagi-Uda antenna can also be used for the better transmission.y Location of the transmitted frequency on the receiver dial requires some patience5.2 Applications

5.2.1 Walkie-talkie:

With a pair of transmitters and a pair of receivers, we can make a walkie-talkie that is

push to talk service (used in first generation of mobile technology).

PERSON-1 PERSON-2

Fig 5.1 Walkie-talkie

y For the first person to initiate the talk, he must push the switch. Pushing the switch, switches


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y ON the transmitter and OFF the receiver-1 the first persons talk will be received by receiver-2 of person-2.

y When the push button is released by the person-1, the transmitter will be switched OFF andreceiver-1 will be ON inviting the person -2 to talk.

y Person -1 must say OVER indicating that he is releasing the push button, this indicatesperson -2 to push the button to take his turn to talk.

y If the person-1 doesnt say over there will be indication for person-2, when to ON histransmitter.

y The push button switch is such that only either of transmitter or receiver will be in ONcondition at a time at particular person, this is because if both transmitter and receiver of same

person are ON then the person receives his own voice from his transmitter to his receiver it

self.

5.2.2 Mini FM station

y One can set-up this transmitter in the institutions like colleges, schools or in an apartments, togive announcements, and songs can be played all over the building premises and can be heard

by people using FM radio in the apartments.

5.2.3 FM-jammer

y FM JAMMER [7] is the circuit used to jam commercial fm-stations near by, up to somerange.

y This is helpful in some colleges and school, where students are not permitted to listenentertainment stations using radios.


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y The FM transmitter can be made as a jammer with small modification.y Just by grounding the oscillator section base input with a 0.1F capacitor.y Grounding capacitor causes bypassing, the input message signal to be grounded, so only a

blank carrier is transmitted, which jams the fm stations.

Fig 5.2 FM transmitter as a jammer

The capacitor shown in Fig 5.2 in the red ink makes the transmitter a jammer.

5.3 Warning:

y It is illegal to transmit the audio in the FM band using transmitters in some countrieslike India.[8]

y The transmitter must be used only for educational purpose, regular using the transmitterwith out proper license is illegal!

y The reason is very obvious, when our transmitter is ON the FM radios surrounding the


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range of our transmitter cannot receive any FM station and they can here only the voice

or audio transmitted by our transmitter because the station and our transmitter both are in

FM band.

Conclusion

The same principle can also be used to transmit video signals over some range; the

transmission is illegal as frequency is in FM band. However using the same modulation technique

but designing the transmitter and receiver for different frequency other than licensed band.One

can use this transmission in railway announcements, apartments, in colleges of seminar halls,

schools, For giving instructions in the constructions of buildings where engineer and worker can

communicate between mores starred buildings.

Result

Voice and audio (music) is transmitted wirelessly, and is reproduced with the FM receiver

(FM radio) over a distance of about 200mts, from the transmitter which is generating

frequency modulated waves.


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Final circuit snap:


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REFERENCES:

[1] Analog communications by Simon Haykin.

[2] Integrated electronics by Jacob Millman and Christos C.Halkias.

[3] Micro electronics by Adel S.Sedra and Kenneth c.smith,5th

edition.

[4] Radio engineering by K.Mittal.

[5] G.S. N raju electronics devices and circuits,1st

edition

[6] Taub and Schilling principles of communication systems, TMH 2nd

edition.

[7] www.circuitstoday.com

[8] www.electronicsforu.com[9] www.wikipedia.com

[10] www.newcircuits.com

[11] www.howeverythingworks.com

[12] www.electronics-madeeasy.blogspot.com

[13] www.williamson-labs.com

[14] www.analog.com

[15] http://www.kpsec.freeuk.com

[16] www.zen22142.zen.co.uk

[17] www.rapidelectronics.com

[18] www.daycounter.com

[19] www.datasheetcatalog.com


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