Why FM Radio gives very clear sound ? Fact File 36


FM frequency is widely used in telecommunication devices to transmit voice without disturbances. Its important feature is the Resilience to signal level variations. The modulation is carried only as variations in frequency. That is, any signal level variations will not affect the audio output, provided that the signal does not fall to a level where the receiver cannot cope. FM wave has property of resilience to noise and interference. It is for this reason that FM is used for high quality broadcast transmissions.

Frequency modulation (FM) is the method of conveying informations over a carrier wave by varying its frequency. FM broadcasting is a broadcast technology invented by Edwin Howard Armstrong to provide high-fidelity sound transmission over broadcast radio. The history of FM dates back to 1936 when Edwin Howard Armstrong described the FM frequency as a method of reducing disturbances in radio transmission in a conference of Radio Engineers New York in November 6, 1936.

Throughout the world, the broadcast band falls within the VHF part of the radio spectrum. Usually 88 – 108 MHz is used. The range of an FM mono transmission is related to the transmitter RF power, the antenna gain and antenna height.For FM stereo, the maximum distance covered is significantly reduced. This is due to the presence of the 38 kHz sub carrier modulation. Vigorous audio processing improves the coverage area of an FM stereo station.

FM is commonly used at VHF radio frequencies for high-fidelity broadcasts of music and speech. Normal TV sound is also broadcast using FM. The FM band used in broadcast is generally called wide-FM, or W-FM. In two-way radio, Narrowband-FM (N-FM) is used to conserve bandwidth. In addition, it is used to send signals into space.

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How Cellphone tapping occurs? Fact File 35


We believe that Cellphone conversation is  private. But it is not so private. It can be tapped from the source. Cellphone tapping may be legal or illegal. Government agencies can collect the details of cellphone conversation to abort illegal activities or as part of law. But so many spying softwares are now available for the illegal intrusion into the privacy of people. These mobile phone Spywares were developed as a measure of Parental control and tracking purpose in emergency situations.

These are mainly used for child safety to watch the online activities of children and to prevent Sexting (Sending or receiving sexually explicit messages).But now the Cell phone spywares are becoming the product of choice for many people who like to eves drop other’s private speech. Using the Cell phone spyware, one can access to all text messages, call history, email and even to listen the live calls.

The Spywares are not the accidental downloading but a deliberate introduction into the phone. The spywares work well in Smart phones, Blackberry, iPhone etc. Here are some symptoms of Spyware attack in our cell phone.

1. If your good battery drops considerably even after regular charging, there is  chance for a spyware. Some spywares continuously send the data from the phone which causes severe battery drain. Don’t be anxious. An old battery shows same symptom.

2. If there is tapping software, clicking sounds will appear between the talks.

3. If your cell phone hesitates to shut down lighting the backlight continuously, there is a possibility of spyware.

4. Frequent lighting of the backlight without any phone activity may be due to a spyware. Don’t be confused. It may be due to poor signals.

5. If there is a background noise during speech or echo, there may be a spying

Don’t worry, we can catch such evesdroppers. There are tricks to find out the spy and destroy it.

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How Mobile phone communicates? Fact File 34


Definitely Mobile phone is an excellent communicating device. But it is not a new invention but the improvisation of the crude wireless device invented by Perry Long in 1940.The first fully Automatic mobile phone system, called MTA (Mobile Telephone system A), was developed by Ericsson and commercially released in Sweden in 1956.

In April 1973, Dr Martin Cooper, former general manager for the systems division at Motorola, invented the mobile phone prototype and he made the first call to Joel Engel, his research rival, head of research at Bell Labs. This is the first Mobile phone call.

Mobile phone is primarily designed for Voice communication. In addition to the standard voice function, new generation mobile phones support many additional services, and accessories, such as SMS ( Short Messaging Service) for text messaging, email, packet switching for access to the Internet, gaming, Bluetooth, camera with video recorder and MMS ( Multi Media Messaging Service) for sending and receiving images, video ,songs etc.

The mobile phone system is referred to as cellular telephone system because the coverage area is divided into “cells “each of which has a base station antenna.The mobile phone tower can communicate to 8 mobile phones in 1 second through time sharing method. The signals are in the form of packets to give two way transmission.

The secret of the mobile phone is its SIM (Subscriber Identification Module).The SIM is a form of digital Smart Card containing the user’s subscription information and a phone book. SIM Securely stores the service subscriber key having 15 digits. First 3 digits indicates Mobile country code, Second 2 digits indicate Mobile network code and the Third 10 digits indicates the Mobile station identification number ( Local station that is connecting).

When you first activates the SIM card, every details like, mobile phone make, pin number, area code, area of activation, server code etc will be recorded automatically in the SIM as well as in the server data base. So it is easy to trace the mobile communication and location if there is a complaint regarding misuse. Let us see what is happening when we use the Cell phone...

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Why ordinary battery is not suitable for Digital camera? Fact File 33


Digital camera is a high drain device consumes large amount of power in each click. Digital camera with LCD and flash light can draw over 1000 mA quickly and depleting the alkaline batteries after a few shots. Alkaline batteries have approximately 3000 mAh capacity with a 1000 mA load. So we have to use a high efficient battery such as NiMH ( Nickel Metal Hydride) battery. NiMH battery outperforms other rechargeable batteries and has higher capacity and less voltage depression. The toxic Cadmium is absent in NiMH battery so it is the most Eco friendly one.

Typical NiMH battery is rated 1.2 volts/cell. This is the nominal voltage of the cell that is discharging at the rate of C/10 at 25 degree centigrade to an end voltage of 1 volt. The battery pack has three 1.2 volt cells making a total 3.6 volts. When a fully charged battery is used, the discharge voltage starts from 1.5 volts followed by a sharp drop to 1.3 volts. The voltage in the cell remains 1.3 volts to 1.2 volts until another voltage drop occurs during a deep discharge.

The NiMH battery is similar to NiCd cells in structure but it uses a hydrogen absorbing alloy as negative electrode instead of cadmium. The positive electrode is a nickel oxy hydroxide (NiOOH).NiMH batteries can easily handle the high current levels and maintain their full capacity. AA type NiMH cells have a nominal capacity (C) ranging from 1000 mAh to 2700 mAh at 1.2 volts with a discharge rate of 0.2C / hour.

Important facts to be considered while using NiMH battery are

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What causes premature battery breakdown? Fact File 32


So many factors. Battery needs care to maintain its chemistry and its energy efficiency. The aging process starts at the moment the battery leaves the manufacturing factory. Self discharge ,sulphation, capacity loss, overcharging, dendrite growth, grid corrosion, excessive heat and water loss etc are some common reasons for the premature battery failure.

If the battery is not cycling for long period, self discharge takes place @ 4 % per week at 27 degree. For example, a 125 Ah battery shows self discharge @ 5 Amps current per week if it is not discharging through the Inverter. Sulphation is another important factor affecting battery efficiency. The lead sulphate accumulating on the plates prevents charge release/ acceptance cycles. Usually the lead sulphate crystals will be removed during water filling and charging. So it is better to charge the battery as soon as possible to prevent sulphation.

Another important reason is overcharging. The battery used in backup systems should have a charger cut off facility, otherwise the battery will get over charged due to float charging. When the battery is overcharged, the charge voltage increases above the Gassing voltage. This causes formation of excess hydrogen. The Gassing voltage of a 12 V lead acid battery is 14.3 at room temperature. The battery voltage crosses the gassing voltage level if one or more cells are damaged or weaker. The weaker cell will charge last since its resistance is lower than the good cells. So higher voltage appears across the good cells and may increase the voltage above the gassing voltage level.

By using the battery equalization method, it is easy to make the battery fully charged. All the cells in the battery will not be equally good due to aging. Some cells accept charge very fast and some in a slow rate. If this happens, the battery will not hold sufficient charge and will discharge very fast through the load. Equalization is done by giving slight overcharge to the battery even after the terminal voltage rises to maximum. Due to this overcharging, the weaker cells also get time to accept full charge. A fully charged 12 volt lead acid battery will show 13.8 V terminal voltage and a 12 V tubular battery will show 14.8 V in the fully charged state.

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