PROJECT

INTRODUCTION

The new FM Wireless Transmitter, It has a better frequency stability, over 1Km

range (under ideal conditions), Tone generator generates a tone which

could be transmitted to wirelessly turn on/off a keypad.

It uses an RF amplifier buffer (with 10dB gain) and an AF preamplifier to boost the modulation a little,

Hartley oscillator is used, Coil is mounted on PCB, It consumes 9V overall power in tranmitter

side, The two BC547 transistors can be replaced

with (almost) any small-signal NPN transistor,

Wired antenna is used which is of fixed length to radiate signals properly.

A random wire antenna is a radio frequency antenna consisting of a wire whose length does not bear a relation to the wavelength of the radio waves used, but is typically chosen more for convenience.

This type of antenna sometimes is called the zig-zag antenna

Folding (to fit in space available) will reduce effectiveness and make theoretical analysis extremely difficult. If used for transmitting.

Although random wire antennas can be made from nearly any length of wire, one-quarter wavelength works best, and one half wavelength will work poorly with most tuners

Tuning of antenna will depend on coil mounted in pcb

Where inductor has a value determined by its radius r, length x and number of wire turns n.

I. The PCB is 50mm x 25mm, II. L1 is 3.25 turns in spiral form and is an

integral part of the PCB foil pattern(fig. a),

III. The circuit as we have already mentioned consists of three stages. Audio preamplifier, Amplifier to boost signal strength for oscillator to work, Hartley Oscillator ,

IV. The frequency of oscillator is controlled by LC network,

V. Finally there is a wired antenna to fed signal for transmission

PLL initially locks to the IF frequencyAfter locking, voltage controlled

oscillator (VCO) would track frequency changes in the input signal by maintaining a phase error

The PLL input is a deviated FM and the VCO natural frequency is equal to the IF center frequency.

In the receiver, unwanted signals and random noise are demodulated along with the message signal: unwanted distortion is produced

Basically number of signals at a time is received in a receiver, with the help of PLL we can fix the frequency of a signal.

By implementing this system, only signal frequency which is transmitted is detected.

The main components of the circuit IC 567(PLL), IC 555(monostable

multivibrator) and UM 66(melody generator).

The Signal o/p taken from FM radio is coupled to i/p of IC 567 through 100nf capacitor.

The o/p of PLL is given to trigger i/p(pin no.2) IC 555,

O/P from PLL is given to i/p of (pin no 3 Vs) melody generator IC UM 66.

IC 567 Wide frequency range

(.01Hz to 500kHz) High stability of center frequencyHigh out-band signal and noise rejectionInherent immunity to false signalsFrequency adjustment over a 20-to-1 range with an externalresistor

IC 555

Basic configuration of 555 timer IC as monostable multivibrator.

UM 66

Programmed for musical performanceVery low power consumptionDesigned for using in door bell, telephone and toy application

The range is increased up to 5 times (from 10 mts. to 100 mts.)

No need of line of sight means you can operate a device from anywhere in the radius of 50 mts.

No need to point transmitter at the receiver. Just press the button from anywhere even if you are in different room or on the different floor the device will be switched ON or OFF.

Resilience to noise The big advantage of FM is its audio quality

and immunity to noise