Wireless FM Microphone

1. INTRODUCTION

           This project just makes a wireless fm microphone which looks very simple in its structure. It is a useful device in our day-today life. A wireless microphone, as the name implies, is a microphone without a physical cable connecting it directly to the sound recording or amplifying equipment with which it is associated. More commonly known as a Radio Microphone, there are many different standards, frequencies and transmission technologies used to replace the microphone's cable connection and make it into a wireless microphone. They can transmit, for example, in radio waves using UHF or VHF frequencies, FM, AM, or various digital modulation schemes. Some low cost models use infrared light. Infrared microphones require a direct line of sight between the microphone and the receiver, while costlier radio frequency models do not. Some models operate on a single fixed frequency, but the more advanced models operate on a user selectable frequency to avoid interference and allow the use of several microphones at the same time. It can be used in seminar halls, class rooms, for a school or college radio etc. One such piece costs 100-300 rupees in the market. The coming sections give the entire idea of making a miniature wireless microphone. We hope that you will find this quite interesting as you go through this particular project.

2. BLOCK DIAGRAM AND ITS DESCRIPTION

POWER SUPPLY

MIC

 

                                                                                                                                         ANTENNA

SIMPLE AUDIO AMPLIFIER

MODULATED TUNED AMPLIFIER

 

                                               

Figure 1: Block Diagram

Above diagram shows the block diagram of the simple wireless fm microphone. It consists of simple audio amplifier, modulated tuned amplifier & a condenser mic.  Here a microphone (condenser) captures the audio signal and a simple audio amplifier amplifies this signal before the modulation is done. A modulated tuned amplifier modulates the signal with self generated carrier frequency. The carrier frequency can be varied by changing the capacitor and inductor value in the tank circuit. Then the modulated signal is fed to the antenna. As a trimmer capacitor is used in the L-C circuit, we can vary the transmitting frequency anywhere in the whole FM band.

       3. COMPONENTS

COMPONENTS	SPECIFICATION	QUANTITY
TRANSISTOR   RESISTOR   CAPACITOR   INDUCTOR	2N3904 10KΩ 1MΩ 100KΩ 100Ω 1KΩ 4.7pF 4-40pF 0.1µF 0.01µ 0.1µH	2 3 1 1 1 1 1 1 2 1 1

4. COMPONENTS DESCRIPTION

4.1 RESISTOR

 A   resistor is a two terminal electronic component that opposes an electric current by producing a voltage drop between its terminals in its terminals in proportion to the current, that is in accordance with Ohm's law: V=IR.  The electrical resistance R is equals to the voltage drop V across the resistor divided by the current / through the resistor. Resistors are used as part of electrical networks and electronic circuits.

4.2 TRANSISTOR

An electrical signal can be amplified by using transistors that allows a small current or voltage to control the flow of a much larger current. In analog circuit transistors are used in oscillator, amplifier and linear regulated power supply. Transistors are also used in digital circuits where they function as electronic switches. Digital circuits include logic gates, RAM and micro processors. Here we use 2N3904 transistor. It is a common NPN bipolar junction transistor. It is used for general purpose low power amplifying and switching applications. It is designed for low current and power, medium voltage and can operate at moderately high speed. This transistor is of low cost and is widely available. When looking at the flat side,with the base pointed downwards, the three wires emerging from the base are, left to right, the emitter ,base and collector leads.

4.3 INDUCTOR

The inductor used in the circuit is a handmade coil using 22 SWG (Standard Wire Gauge) enameled copper wire. The length, inner diameter, number of turns etc are the important parameters to be considered while making the inductor. Then only the inductor resonates in the 88-108 band FM frequency. For this circuit, the coil radius was selected as 0.26 inches (outer diameter) and 0.13 inner diameter. Coil can be wound around a screw driver (with same diameter) to get a 5 turn    coil of   0.2

inch long. Remove the coil from the screw driver and use the 5 turn Air core coil. Remove the enamel from the tips and solder close to the transistor.

The inductance of the coil can be calculated using the formula :

L =n²r²/ (9r + 10 x)

Where r is the inner radius of the coil, x is the length of the coil and n, number of turns. The resulting value is in Micro Henry.

An inductor is just a coil of wire and you need to wind one for this circuit. An inductor is characterized by its length, radius and the number of turns of wire in the coil. Magnet wire (Radio Shack part 278-1345) was used to build the inductor but you can use standard solid strand 22 AWG gauge copper wire. Some on-line and printed articles describe winding the wire around a pencil. Unfortunately, pencils come in different diameters and hence a McDonald’s soda straw was used; the yellow-red-white striped straw, found in every McDonalds in the world, is the same size. The straw’s radius is exactly 0.1325 inches (diameter = 0.2650 inches) and 1/4 inches was snipped off the straw.

4. 4 CONDENSER MIC

The condenser MIC is used to pick up the sound signals. The diaphragm inside the MIC vibrates according to the air pressure changes and generates AC signals. Variable resistor VR1 adjusts the current through the MIC and thus determines the sensitivity of MIC. The condenser MIC should be directly soldered on the PCB to get maximum sensitivity. Sleeving the MIC inside plastic tubing can increase its sensitivity error.

4.5 CAPACITOR

A capacitor is an electrical/electronic device that can store energy in the electric field between a pair of conductors (called "plates"). The process of storing

energy in the capacitor is known as "charging", and involves electric charges of equal magnitude, but opposite polarity, building up on each plate. Capacitors are often used in electric and electronic circuits as energy-storage devices. They can also be used to differentiate between high-frequency and low-frequency signals. This property makes them useful in electronic filters. Practical capacitors have series resistance, internal leakage of charge, series inductance and other non-ideal properties not found in a theoretical, ideal, capacitor.

4.6 TRIMMER CAPACITOR

A small button type variable capacitor with a value of 40 pF can be used to adjust the resonant frequency of the tank circuit. The variable capacitor and the inductor coil form the Tank circuit (LC circuit) that resonates in the 88-108 MHz. In the tank circuit, the capacitor stores electrical energy between its plates while the inductor stores magnetic energy induced by the windings of the coil. The resonant frequency can be calculated using the formula:

f = 1 / 2 π √LC = Hz

Where f is the frequency in hertz, x is the coil length, C is the capacitance of trimmer in Farads, and L is the inductance of coil in Henry.

4.7 TANK CIRCUIT

Every FM transmitter needs an oscillator to generate the radio Frequency (RF) carrier waves. The name ‘Tank’ circuit comes from the ability of the LC circuit to store energy for oscillations. The purely reactive elements, the C and the L simply store energy to be returned to the system. In the tank (LC) circuit, the 2N3904 transistor and the feedback 4.7 pF capacitor are the oscillating components. The feedback signal makes the base-emitter current of the transistor vary at the resonant frequency. This causes the emitter-collector current to vary at the same frequency. This signal fed to the aerial and radiated as radio waves.

4.8 ANTENNA

A plastic wire or Telescopic aerial can be used as antenna. The length of the antenna is very important to transmit the signals in the suitable range. As a rule, the length of the antenna should be ¼ of the FM wave length. To determine the length of antenna, use the following equation. By multiplying the Wave frequency and wave length will give the speed of light.

Speed of Light = Frequency of Oscillation x Wavelength = in kms/ sec

Wave length = Speed of light / Frequency = in meters
Antenna length = 0.25 x wavelength = in meters

By using this formula it is easy to select the antennal length. For the circuit mentioned above, a 25-27inches long antenna is sufficient.      

                

 5. FM (FREQUENCY MODULATION)

In telecommunications and signal processing, frequency modulation (FM) conveys information over a carrier wave by varying its instantaneous frequency. This is in contrast with amplitude modulation, in which the amplitude of the carrier is varied while its frequency remains constant.

In analog applications, the difference between the instantaneous and the base frequency of the carrier is directly proportional to the instantaneous value of the input signal amplitude. Digital data can be sent by shifting the carrier's frequency among a set of discrete values, a technique known as frequency-shift keying.Frequency modulation can be regarded as phase modulation where the carrier phase modulation is the time integral of the FM modulating signal.

FM is widely used for broadcasting of music and speech, and in two-way radio systems, in magnetic tape recording systems, and certain video transmission systems. In radio systems, frequency modulation with sufficient bandwidth provides an advantage in cancelling naturally-occurring noise.

Frequency-shift keying (digital FM) is widely used in data and fax modems.

Waveforms:

 

A Signal may be carried by an AM or FM Radio wave

 

 

 

Signal modify the Frequency of a carrier in FM

5.1 THEORY

Suppose the baseband data signal (the message) to be transmitted is x_m(t) and the sinusoidal carrier is  , where f_c is the carrier's base frequency and A_c is the carrier's amplitude. The modulator combines the carrier with the baseband data signal to get the transmitted signal:

  

          

          

In this equation,   is the instantaneous frequency of the oscillator and   is the frequency deviation, which represents the maximum shift away from f_c in one direction, assuming x_m(t) is limited to the range ±1.

Although it may seem that this limits the frequencies in use to f_c ± f_Δ, this neglects the distinction between instantaneous frequency and spectral frequency. The frequency spectrum of an actual FM signal has components extending out to infinite frequency, although they become negligibly small beyond a point.

5.1.1 SINUSOIDAL BASEBAND SIGNAL

While it is an over-simplification, a baseband modulated signal may be approximated by a sinusoidal Continuous Wave signal with a frequency f_m. The integral of such a signal is,

Thus, in this specific case, equation (1) above simplifies to:

where the amplitude   of the modulating sinusoid, is represented by the peak deviation   (see frequency deviation.

The harmonic distribution of a sine wave carrier modulated by such a sinusoidal signal can be represented with Bessel functions - this provides a basis for a mathematical understanding of frequency modulation in the frequency domain.

5.2 MODULATION INDEX

As with other modulation indices, this quantity indicates by how much the modulated variable varies around its un-modulated level. It relates to the variations in the frequency of the carrier signal:

where   is the highest frequency component present in the modulating signal x_m(t), and   is the   Peak   frequency-deviation, i.e.   the     maximum    deviation of the

 instantaneous frequency from the carrier frequency. If   , the modulation is called narrowband FM, and its bandwidth is approximately  .

           If  , the modulation is called wideband FM and its bandwidth is approximately  . While wideband FM uses more bandwidth, it can improve signal-to-noise ratio significantly. For example, doubling the value of   while keeping f_m constant, results in an eight-fold improvement in the signal to noise ratio. Compare with Chirp spread spectrum, which uses extremely wide frequency deviations to achieve processing gains comparable to more traditional, better-known spread spectrum modes.

            With a tone-modulated FM wave, if the modulation frequency is held constant and the modulation index is increased, the (non-negligible) bandwidth of the FM signal increases, but the spacing between spectra stays the same; some spectral components  decrease in strength as others increase. If the frequency deviation is held constant and the modulation frequency increased, the spacing between spectra increases.

           Frequency modulation can be classified as narrow band if the change in the carrier frequency is about the same as the signal frequency, or as wide-band if the change in the carrier frequency is much higher (modulation index >1) than the signal frequency.  For example, narrowband FM is used for two way radio systems such as Family Radio Service where the carrier is allowed to deviate only 2.5 kHz above and below the center frequency, carrying speech signals of no more than 3.5 kHz bandwidth. Wide-band FM is used for FM broadcasting where music and speech is transmitted with up to 75 kHz deviation from the center frequency, carrying audio with up to 20 kHz bandwidth.

     5.3 CARSON'S RULE

           A rule of thumb, Carson's rule states that nearly all (~98%) of the power of a frequency-modulated signal lies within a bandwidth   of

where  , as defined above, is the peak deviation of the instantaneous frequency   from the center carrier frequency  .

Noise quieting

             The noise power decreases as the signal power increases; therefore the SNR goes up significantly.

  5.4 MODULATION

              FM signals can be generated using either direct or indirect frequency modulation.

·         Direct FM modulation can be achieved by directly feeding the message into the input of a VCO.

·         For indirect FM modulation, the message signal is integrated to generate a phase modulated signal. This is used to modulate a crystal controlled oscillator, and the result is passed through a frequency multiplier to give an FM signal.

 

       5.5 DEMODULATION

              Many FM detector circuits exist. One common method for recovering the information signal is through a Foster-Seeley discriminator. A phase-locked loop can be used as an FM demodulator.  Slope detection demodulates an FM signal by using a tuned circuit, which has its resonant frequency slightly offset from the carrier frequency. As the frequency rises and falls, the tuned circuit provides a changing amplitude of response, converting FM to AM. AM receivers may detect some FM transmissions by this means, though it does not provide an efficient method of detection for FM broadcasts.

                  

     5.6. SOUND

            FM is also used at audio frequencies to synthesize sound. This technique, known as FM synthesis, was popularized by early digital synthesizers and became a standard feature for several generations of personal computer sound cards.

     5.7 RADIO

            Edwin Howard Armstrong (1890–1954) was an American electrical engineer who invented wideband frequency modulation (FM) radio. He patented the regenerative circuit in 1914, the super-heterodyne receiver in 1918 and the super-regenerative circuit in 1922. He presented his paper: "A Method of Reducing Disturbances in Radio Signaling by a System of Frequency Modulation", which first described FM radio, before the New York section of the Institute of Radio Engineers on November 6, 1935. The paper was published in 1936.

            As the name implies, wideband FM (WFM) requires a wider signal bandwidth than amplitude modulation by an equivalent modulating signal, but this also makes the signal more robust against noise and interference. Frequency modulation is also more robust against simple signal amplitude fading phenomena. As a result, FM was chosen as the modulation standard for high frequency, high fidelity radio transmission: hence the term "FM radio" (although for many years the BBC called it "VHF radio", because commercial FM broadcasting uses a well-known part of the VHF band—the FM broadcast band).FM receivers employ a special detector for FM signals and exhibit a phenomenon called capture effect, where the tuner is able to clearly receive the stronger of two stations being broadcast on the same frequency. Problematically however, frequency drift or lack of selectivity may cause one station or signal to be suddenly overtaken by another on an adjacent channel. Frequency drift typically constituted a problem on very old or inexpensive receivers, while inadequate selectivity may plague any tuner.

           

            An FM signal can also be used to carry a stereo signal: see FM stereo. However, this is done by using multiplexing and de-multiplexing before and after the FM process. The rest of this article ignores the stereo multiplexing and de-multiplexing process used in "stereo FM", and concentrates on the FM modulation and demodulation process, which is identical in stereo and mono processes.

            A high-efficiency radio-frequency switching amplifier can be used to transmit FM signals (and other constant-amplitude signals). For a given signal strength (measured at the receiver antenna), switching amplifiers use less battery power and typically cost less than a linear amplifier. This gives FM another advantage over other modulation schemes that require linear amplifiers, such as AM and QAM.

      5.8 MISCELLANEOUS

            Frequency-shift keying is the frequency modulation using only a discrete number of frequencies. Morse code transmission has been implemented this way, as were most early telephone-line modems Radio teletype also use FSK.

FM modulation is also used in telemetry applications, radar, seismic prospecting and newborn EEG seizures modeling.

5.9 SUPER HETERODYNE RECIEVER

In electronics, a super heterodyne receiver (sometimes shortened to superhets) uses frequency mixing or heterodyning to convert a received signal to a fixed intermediate frequency, which can be more conveniently processed than the original radio carrier frequency. Virtually all modern radio and television receivers use the super heterodyne principle.

The diagram at right shows the minimum requirements for a single-conversion super heterodyne receiver design. The following essential elements are common to all superhet circuits:^[ a receiving antenna, a tuned stage which may optionally contain amplification (RF amplifier), a variable frequency local oscillator, a frequency mixer, a band pass filter and intermediate frequency (IF) amplifier, and a demodulator plus

additional circuitry to amplify or process the original audio signal (or other transmitted information).

 

Figure : Block Diagram of Super heterodyne Receiver

 

5.10 CIRCUIT DESCRIPTION

To receive a radio signal, a suitable antenna is required. This is often built into a receiver, especially in the case of AM broadcast band radios. The output of the antenna may be very small, often only a few microvolts. The signal from the antenna is tuned and may be amplified in a so-called radio frequency (RF) amplifier, although this stage is often omitted. One or more tuned circuits at this stage block frequencies which are far removed from the intended reception frequency. In order to tune the receiver to a particular station, the frequency of the local oscillator is controlled by the tuning knob (for instance). Tuning of the local oscillator and the RF stage may use a variable capacitor, or varicap diode. The tuning of one (or more) tuned circuits in the RF stage must track the tuning of the local oscillator.

5.11 MIXER STAGE

The signal is then fed into a circuit where it is mixed with a sine wave from a variable frequency oscillator known as the local oscillator (LO). The mixer uses a non-linear component to produce both sum and difference beat frequencies signals, each one containing the modulation contained in the desired signal. The output of the mixer may include the original RF signal at f_d, the local

oscillator signal at f_LO, and the two new frequencies f_d+f_LO and f_d-f_LO. The mixer may inadvertently produce additional frequencies such as 3rd- and higher-order intermediation products. The undesired signals are removed by the IF bandpass filter, leaving only the desired offset IF signal at f_IF which contains the original modulation (transmitted information) as the received radio signal had at f_d.

Historically, broadcast AM receivers using vacuum tubes would save costs by employing a single tube as a mixer and also as the local oscillator. The pentagrid converter tube would oscillate and also provide signal amplification as well as frequency shifting.

5.12 INTERMEDIATE FREQUENCY STAGE

The stages of an intermediate frequency amplifier are tuned to a particular frequency not dependent on the receiving frequency; this greatly simplifies optimization of the circuit. The IF amplifier (or IF strip) can be made highly selective around its center frequency f_IF, whereas achieving such a selectivity at a much higher RF frequency would be much more difficult. By tuning the frequency of the local oscillator f_LO, the resulting difference frequency f_LO - f_d (or f_d-f_LO when using so-called low-side injection) will be matched to the IF amplifier's frequencyf_IF for the desired reception frequency f_d. One section of the tuning capacitor will thus adjust the local oscillator's frequency f_LO to f_d + f_IF (or. less often, to f_d - f_IF) while the RF stage is tuned to f_d. Engineering the multi-section tuning capacitor and coils to fulfill this condition across the tuning range is known as tracking.Other signals produced by the mixer (such as due to stations at nearby frequencies) can be very well filtered out in the IF stage, giving the superheterodyne receiver its superior performance. However, if f_LO is set to f_d + f_IF , then an incoming radio signal at f_LO + f_IF will also produce a heterodyne at f_IF; this is called the image frequency and must be rejected by the tuned circuits in the RF stage. The image frequency is 2f_IF higher (or lower) than f_d, so employing a higher IF frequency f_IF increases the receiver's image rejection without requiring additional selectivity in the RF stage.

Usually the intermediate frequency is lower than the reception frequency f_d, but in some modern receivers (e.g. scanners and spectrum analyzers) it is more convenient to first convert an entire band to a much higher intermediate frequency; this eliminates the problem of image rejection. Then a tunable local oscillator and mixer converts that signal to a second much lower intermediate frequency where the selectivity of the receiver is accomplished. In order to avoid interference to receivers, licensing authorities will avoid assigning common

IF frequencies to transmitting stations. Standard intermediate frequencies used are 455 KHz for medium-wave AM radio, 10.7 MHz for broadcast FM receivers, 38.9 MHz (Europe) or 45 MHz (US) for television, and 70 MHz for satellite and terrestrial microwave equipment.

5.13 BANDPASS FILTER

            The received The IF stage includes a filter and/or multiple tuned circuits in order to achieve the desired selectivity. This filtering must therefore have a band pass equal to or less than the frequency spacing between adjacent broadcast channels. Ideally a filter would have a high attenuation to adjacent channels, but maintain a flat response across the desired signal spectrum in order to retain the quality of signal. This may be obtained using one or more dual tuned IF transformers or a multipole ceramic crystal filter.

5.14 DEMODULATION

The received signal is now processed by the demodulator stage where the audio signal (or other baseband signal) is recovered and then further amplified. AM

demodulation requires the simple rectification of the RF signal (so-called envelope detection), and a simple RC low pass filter to remove remnants of the intermediate frequency. FM signals may be detected using a discriminator, ratio detector, or phase-locked loop. Continuous wave (morse code) and single sideband signals require a product detector using a so-called beat frequency oscillator, and there are other

techniques used for different types of modulation. The resulting audio signal (for instance) is then amplified and drives a loudspeaker. When so-called high-side injection has been used, where the local oscillator is at a higher frequency than the received signal (as is common), then the frequency spectrum of the original signal will be reversed. This must be taken into account by the demodulator (and in the IF filtering) in the case of certain types of modulation such as single sideband.

6. CIRCUIT DIAGRAM OF   WIRELESS FM     MICROPHONE

7. CIRCUIT DESCRIPTION

The above figure shows the circuit diagram of wireless FM microphone .It has two transistor stages. The first one is the common emitter amplifier .The second stage is the voltage controlled oscillator. Capacitor and self-made inductor will vibrate at frequencies in the FM radio band (88 to 108 MHz) and it constitutes the L-C circuit. It is also called tank circuit. It consists of one inductor and two capacitors. This is called Colpitt's oscillator. The physics lying behind this is that the capacitor stores charges between its plates, while the inductor coil stores energy in the magnetic field induced by the coil winding. The tank circuit vibrates at resonant frequency. The resonant frequency is given by

f = 1 / 2 π √LC Hz

Where f is the frequency in hertz, C is the capacitance of trimmer in Farads, and L is the inductance of coil in Henry. The performance of an FM transmitter depends on two important aspects

·         Tuning of the FM transmitter to the desired frequency. Even a slight change in the coil    specification or slight change in the variable capacitor value can shift the harmonic frequency of  the 88 to 108 MHz FM band.

·         Length of the Antenna used to transmit the frequency.

The important parameters for the optimum performance of an FM transmitter are :

·         Transmitter frequency, output power and range of transmission.

·         Antenna length.

·         Coil diameter, length, number of turns and gauge of the wire used for coil winding.

The electric microphone has a resistance that depends on how loudly you speak into it. This microphone is battery powered and according to the V=IR Ohm’s Law,

changes in resistance for fixed voltage will result in proportional changes in current. This wireless FM microphone is easy to construct and its transmissions can be picked up on any standard FM radio. It has a range of up to 1/4-mile (400 meters) or more, depending on the   line of sight, obstructions by large buildings, etc.  If you decide to substitute transistors with something similar you already have, it may be necessary to adjust the collector voltage of Q1 by changing the value of R2 or R3 (because you change transistors, it changes this bias on the base of Q1). It should be about half the supply voltage (about 4 or 5). To find the signal on receiver, make sure there is a signal coming in to the microphone, otherwise the circuit won't work.

          To use the microphone, set up a radio in the area at least 10 feet (3 meters) from the project. Find a blank spot on the FM dial and tune the radio up so you can hear the static. Connect a 9-volt battery to the transmitter and listed to the radio. Slowly adjust the trimmer capacitor until "quiet" the receiver; this is the tuned spot.  When move hand from the transmitter, then detune the circuit somewhat. It is usually best to leave it detuned and tune the radio in to get the best reception. If you get the tuning range you desire, you can squeeze the coils in the tank circuit closer together to raise the frequency, or pull them apart just a little to lower it.

8. PCB DESIGN

8. 1 PCB   DESIGN PROCEDURE

PCB preparation can be done using the following steps.

·         Prepare the PCB layout of the circuit in a graph sheet.

·         Cut the copper clad sheet in proper dimension and wash it.

·         PCB layout is coated with paint or sticker.

·         Prepare the ferric chloride solution

·         Dip the PCB in to Ferric chloride solution for etching non printed surface.

·         Wash cleanly with detergent.

·         Drill the holes in necessary any position.

                              

9. PCB LAYOUT

10. SOLDERING

Soldering is the process of joining two or more similar or dissimilar maters by melting another meters having lower melting points. Soldering is an alloy of tin and lead, used for fusing the metals at relatively low temperature about 260uk to 315uk.The joint where the two metal conductors are to be fused is heated and solder is applied so that it can melt and cover the connection. The reason for soldering connections is that it makes a good bond between the joining metals , covering the joints completely to prevent oxidization. The coating of solder provides protection for practically long period of time. The trick in soldering is to heat the joint, not the solder. When the soldering is hot enough to melt the solder, it follows smoothly to fill all cracks forming a shiny cover without any space. Do not move the joint until the solder has set. Either the soldering iron or soldering gun can be used rated at 25W to 100W.In addition to this solder flux is used to remove any oxide films on the metal being joint. Otherwise they cannot be joined together.

9.1 SOLDERING FLUXES

In order to make the surface accept the solder readily, the component terminals should be for from order and other abstractly films. Soldering flux cleans the orders from the surface of the metal. Zinc chloride, aluminums chloride, and rosin at the commonly used fluxes.

9.2 SOLDER

Solder is used for joining two or more mental at temperature below their melting point. The popularly used solders on alloy are alloys of tin (60%) and lead (40%) that metals at stiff and solidifies when it cools.

9.3 SOLDERING IRON

It is used the melt the solder and apply at the joints in the circuit.

11. ADVANTAGE

Ø  Working with a simple dry cell power supply.

Ø  It is user friendly.

Ø  Low cost.

Ø  Easy to install.

Ø  Simple circuit.

Ø  Greater freedom of movement for the artist or speaker.

Ø  Avoidance of cabling problems common with wired microphones, caused by constant moving and stressing the cables.

12. DISADVANTAGE         

Ø  Sometimes limited range (a wired balanced XLR microphone can run up to 300 ft or 100 meters). Some wireless systems have a shorter range, while more expensive models can exceed that distance.

Ø  Possible interference with or, more often, from other radio equipment or other radio microphones, though models with many frequency-synthesized switch-selectable channels are now plentiful and cost effective.

Ø  Operation time is limited relative to battery life; it is shorter than a normal condenser microphone due to greater drain on batteries from transmitting circuitry, and from circuitry giving extra features, if present.

Ø  Noise or dead spots (places where it doesn't work, especially in non-diversity systems).

Ø  Limited number of operating microphones at the same time and place, due to the limited number of radio channels (frequencies).

13. APPLICATION

Ø  It is used in seminar halls, class rooms, for a school or college radio etc.

Ø  

14. CONCLUSION

The mini project 'wireless FM microphone' is developed from the elementary idea of making a wireless hand piece, which can be used in a seminar hall, auditorium etc. This idea forced us to proceed with our project. As our project deals with transmitter & the most common receiver is FM receiver, we decided to make the FM Transmitter.

15. FUTURE SCOPE

As the field of Information Technology and Communication is developing day-by-day, the necessity of more sophisticated equipments and discoveries is raising up. Hence, more enhanced version of our project, wireless FM microphone can be implemented in various circuits.

APPENDIX