Beverage antenna

Herold beverage discovered in 20 that an otherwise nearly bidirectional long wire antenna becomes uni-directional by placing it close to the lossy earth and by terminating one end of the wire with a non-inductive resistor with a resistance approximately matched to the characteristics or surge impedance of the antenna. This was the fundamental discovery in his 1921 patent. From the transmission line theory we know that the line terminated with load impedance equal to characteristic impedance (Z๐), there is only a traveling wave present on the line. Since there is no reflected wave, there is no standing wave on the line. Then the line is said to be non resonant.

   

It consists of a wire one or two wavelength long. Note that the length of 1 or 2λ is not a small length at LF or MF; it is hundreds of feet at MF to several kilometers for LF. The wire runs parallel to the earth’s surface from the receiver towards the direction of the desired signal. The wire is suspended by insulated supports approximately two meters above the ground. A non-inductive resistor of value equal to characteristic impedance is installed from the far end of the wire to the ground. As the wire is properly terminated, the structure becomes a non resonant antenna.

Emulator

An emulator is a piece of hardware that is placed into application circuit to run and observe that operation of the system without developing stimulus files.

Types of emulators 

Software emulators: 

A software emulator allows computer programs to run on a platform (computer architecture and/ or operating system) other than the one for which they were originally written. Unlike simulation, which only attempts to reproduce a program’s behavior, emulation attempts to model to various degrees the state of the device being emulated. High- level emulation uses a combination of the two approaches in an attempt to retain as much accuracy as possible while having the advantages of simplicity and speed provided by simulation. 

Hardware emulator:

A hardware emulator is an emulator which takes the form of a hardware device. Examples include printer emulators inside the ROM of the printer, and FPGA based emulators.

A popular use of emulators is to mimic the experience of running arcade games or console games on personal computers. Emulating these on modern desktop computers is usually less cumbersome and more reliable than relaying on the original machines, which are often old and hard to find. Emulation of arcade and console systems on home PCs usually includes the practice of illegally downloading software from various electronic distribution sources. 

In a theoretical sense, any operating environment can be emulated within any other. In practice, it can be quite difficult, particularly when the exact behavior of the system to be emulated is not documented and has to be deduced through reverse engineering. It also says nothing about timing constraints; if the emulator does not perform as quickly as the original hardware, the emulated software may run much more slowly than it would have on the original hardware, or it may run too fast to be usable.

Simulators

A simulator is a program that simulates the functioning of electronic circuits. Simulator allows the designer to determine the correctness and efficiency of a design before the system is actually constructed.

 

A stimulus file is used for simulating input from external hardware. The stimulus file provides a series of inputs to the simulator to observe the overall behavior of system. The stimulus file for micro controller process consists for cycle counter and pin states.

An important consideration while selecting a simulator is its execution speed i.e. how fast it can execute the application’s instructions. If the execution speed of simulator is less compare to the processor then the simulator may take hours in a simulated environment. The delay may be due to complex interactions within the system being simulated. Therefore the simulator’s result are deviated from the actual operation.

Unit Loudspeaker

    For public address and street announcement purpose we require such type of loudspeaker and a power amplifier which can reproduce the sound waves up to thousand of listeners in a public place. The loudspeaker used for the purposes is called unit loudspeaker. it consists of following two main parts.

1.       Pressure units: Its construction is similar to that or p.m. dynamic loudspeaker. The difference is that it has a large voice coil with a small cone. The impedance of voice coil may be up to 160 ohms whereas the impedance of an ordinary loudspeaker is not more than 20 ohms. It employs metallic cone in place of a paper cone. The power rating of a pressure unit varies between 16 and 20 watts whereas that of an ordinary loudspeaker lies between 3 to 8 watts.

            The pressure units convert the a.f. voltage received from an a. f. amplifier into powerful sound waves. It is known as drive unit.

Horn: if the sound waves reproduced by a pressure unit are allowed to radiate directly in the atmosphere then they would not be able sound waves in a hemisphere then they would not be able sound waves in a hemisphere area only around it. A pressure unit radiates the of aluminum sheet is attached to the pressure unit. The horn converts sound waves of low pressure and high pressure and low velocity in to sound waves of low pressure and high velocity.

            A horn is constructed in such a way that its diameter from its throat to mouth increase in a parabolic or exponential ratio. The total length of an ordinary type of horn is large enough and it does not suit for it to be used on vehicles. Hence, the horns on vehicles are of reflex or folded type. In a reflex horn, the total length of the horn is divided in to two parts and both the parts are fitted in such a way that the total length of the horn is reduced to almost half, whereas its effective length remains the same as of an original type.

COLUMN SPEAKER 

         It is almost impossible to reproduce the entire a.f. range of 20Hz to 20 KHz with a single loudspeaker, even more; the reproduction of the practical a.f. range of 30 Hz to 12 KHz with a single loudspeaker is quite difficult. If the size of the cone is kept between 25 to 35cm then it can reproduce frequencies above 8,000 Hz at the same level. Similarly, if the size of the between 5 to 15  cm then it can reproduce frequencies of the a.f. range of 8000 Hz to 20,000 Hz is reduced to lower level. Hence, the following two alternatives are employed for the faithful and equal level reproduction of the a.f. range of 30 Hz to 12 KHz.  

1.       Coaxial and Triaxial speaker: 

 A coaxial speaker consists of two cones of small and large sizes respectively fitted on the same axis. The smaller speaker is called tweeter and the larger one is called woofer. Tweeter improves high frequency reproduction while woofer improves low frequency reproduction.

               Similarly, a triaxial speaker consists of tweeter for high frequencies, a diaphragm for medium frequencies and woofer for low frequencies.

2.       Multi speaker system  : In this system two of three speakers of different sizes, especially designed to produce maximum output for a low pass filter (a choke of suitable value or a MFD value capacitor) is connected in series with the woofer. Similarly, a high pass filter ( a paper capacitor of suitable value) is connected in series with the tweeter. A box consisting more than one speaker is also known as column speaker.

Microphone mirror

               In sound recording, for adding the echos to the fundamental sound of a singer, polished metallic reflectors are used which are called microphone are also microphone mirrors. Besides, it high impedance microphones are called microphone mirrors. 

Earphone

     A headphone consists of two receiver units joined together with an iron strip in such a way that the strip rests on the head and both the receiver units  rest  close to the  ears of the listener. An earphone consists if a single receiver unit. Some earphones are made so small in size that they can be easily fitted inside the external cavity of the ear.

    An earphone is the miniature form of a loudspeaker. It is used with transistorized receivers and hearings aids.

Loudspeaker

The instrument which converts electrical a.f. waves into sound waves is called a loudspeaker. there are mainly following two types of loudspeakers:

1     Magnetic loudspeaker 

2    Dynamic loudspeaker

1.       Magnetic loudspeaker: It consists of a permanent magnet and a voice coil wound on it. A diaphragm made of fine iron sheet and a paper cone is mounted in front of the magnet. Its working is identical to that of headphone. It is also known as cone type loudspeaker.

Sometimes, a horn is also attached to the loudspeaker for increasing the loudness of the sound. Such loudspeaker is called horn type loudspeakers.

Both the above explained loudspeakers are outdated since the performance of dynamic loudspeaker is more satisfactory than magnetic loudspeakers.

2.       Dynamic loudspeaker: This type of loudspeaker consists of moving or dynamic loudspeakers. There are following two types of loudspeakers :

1.      Permanent magnet dynamic loudspeakers :

2.       Electro magnet dynamic loudspeakers :

Permanent Magnet Dynamic Loudspeaker   

1.       Principle. If two magnetic fields are acting at one place than a magnet or magnetic field producing coil can be moved of vibrated due to attraction or repulsion between the two fields.

2.       Construction: Its construction is similar to that of a dynamic microphone. The only difference is this that the size of loudspeaker is much bigger than that of a microphone. The diameter of the cone of a microphone is usually 2-3 cm while that of a loudspeaker is usually 3 to 30 cm. it employs an ALNICO magnet. 

3.       Working: the voice coil established an alternating magnetic field on applying a.f. voltage to it. The coils magnetic field will start to be added to or subtracted from the magnetic field of the permanent magnet consequently, the voice coil will start to vibrate to and fro. The cone sound waves. The frequency and amplitude of cones vibration and the corresponding sound waves are exact replica of a.f. waves applied.

4.       Users: Loudspeaker are used for listening a broadcast program from a receiver or for listening a public address through an a.f. amplifier by more than one person at a time.

Electro Magnet Dynamic Loudspeaker  

   In this of loudspeaker an electromagnet is used in place of the loudspeaker construction is the is same as of a p. m. dynamic loudspeaker.

       The coil used in electromagnetic is called humbeking coil of field coil. It is excited with a D.C. source. This type of loudspeaker were used in early type of receiver since the technique of making small sized powerful permanent magnets was not developed till then. Now, those loudspeakers are obsolete.