Electronic and Communications Interview Questions - Part 2
Difference between mobile and a cell phone.
There is no difference, just language use, which differs from country to country, so in Britain it is called a mobile, and in USA and South Africa and other places a cell phone. Even in Europe the name differs. The Germans call it a "handy", which in English has completely another meaning as an adjective, meaning useful. In Italy it is called a telofonino or "little phone". This difference in British and American English is also evident in many other things we use every day, like lifts and elevators, nappies and diapers, pickups and trucks. The list goes on and on, any student of English has to decide which he or she will use, as the default setting.
Explain RF ?
Radio frequency (RF) is a frequency or rate of oscillation within the range of about 3 Hz to 300 GHz. This range corresponds to frequency of alternating current electrical signals used to produce and detect radio waves. Since most of this range is beyond the vibration rate that most mechanical systems can respond to, RF usually refers to oscillations in electrical circuits or electromagnetic radiation.
What is modulation? And where it is utilized?
Modulation is the process of varying some characteristic of a periodic wave with an external signals. Radio communication superimposes this information bearing signal onto a carrier signal.These high frequency carrier signals can be transmitted over the air easily and are capable of travelling long distances. The characteristics (amplitude, frequency, or phase) of the carrier signal are varied in accordance with the information bearing signal. Modulation is utilized to send an information bearing signal over long distances.
What is demodulation ?
Demodulation is the act of removing the modulation from an analog signal to get the original baseband signal back. Demodulating is necessary because the receiver system receives a modulated signal with specific characteristics and it needs to turn it to base-band.
Name the modulation techniques.
For Analog modulation--AM, SSB, FM, PM and SM Digital modulation--OOK, FSK, ASK, Psk, QAM, MSK, CPM, PPM, TCM, OFDM
Explain AM and FM.
AM-Amplitude modulation is a type of modulation where the amplitude of the carrier signal is varied in accordance with the information bearing signal. FM-Frequency modulation is a type of modulation where the frequency of the carrier signal is varied in accordance with the information bearing signal.
Where do we use AM and FM ?
AM is used for video signals for example TV. Ranges from 535 to 1705 kHz. FM is used for audio signals for example Radio. Ranges from 88 to 108 MHz.
How does a mobile work ?
When you talk into a mobile telephone it converts the sound of your voice to radiofrequency energy (radio waves). The radio waves are transmitted through the air to a nearby base station . The base station then sends the call through the telephone network until it reaches the person you are calling. When you receive a call on your mobile phone the message travels through the telephone network until it reaches a base station near to you. The base station sends out radio waves, which are detected by your telephone and converted back to speech. Depending on the equipment and the operator, the frequency that each operator utilises is 900MHz, 1800MHz or 2100MHz. The mobile phone network operates on the basis of a series of cells. Each cell requires a radio base station to enable it to function. There are three types of base station and each has a particular purpose:
The Macrocell is the largest type and provides the main coverage for mobile phone networks.
The Microcell is used to improve capacity in areas where demand to make calls is high, such as shopping centers.
The Picocell only has a range of a few hundred metres and may be used to boost weak signals within large buildings.
Each base station can only cope with a certain number of calls at any one time. So if demandexceeds the capacity of a base station an additional base station is needed.
What is a base station ?
Base station is a radio receiver /transmitter that serves as the hub of the local wireless network, and may also be the gateway between a wired network and the wireless network.
How many satellites are required to cover the earth ?
3 satellites are required to cover the entire earth, which is placed at 120 degree to each other. The life span of the satellite is about 15 years.