Electronic and Communications Interview Questions - Part 8
What is EDFA ?
Erbium Doped Fiber Amplifier (EDFA) A device that boosts the signal in an optical fiber. EDFA is an optical repeater device that is used to boost the intensity of optical signals being carried through a fiber optic communications system. An optical fiber is doped with the rare earth element erbium so that the glass fiber can absorb light at one frequency and emit light at another frequency. An external semiconductor laser couples light into the fiber at infrared wavelengths of either 980 or 1480 nanometers. This action excites the erbium atoms. Additional optical signals at wavelengths between 1530 and 1620 nanometers enter the fiber and stimulate the excited erbium atoms to emit photons at the same wavelength as the incoming signal. This action amplifies a weak optical signal to a higher power, effecting a boost in the signal strength.
What are different types of antennas ?
An antenna (or aerial) is a transducer that transmits or receives electromagnetic waves. In other words, antennas convert electromagnetic radiation into electric current, or vice versa. They are used to transmit and receive electromagnetic radiation of radio frequency, that is, radio waves, and are a necessary part of all radio equipment There are different types of antennas, they can mainly divided into directional & undirectional a simply type of directional antennas: helical antenna a simple type of undirectional antennas: yagi & loop antennas
What is Yagi-Uda antenna ?
Directional antenna systemconsisting of an array of a dipole and additional closely coupled parasitic elements (usually a reflector and one or more directors). The dipole in the array is driven, and another element, typically 5% longer, effectively operates as a reflector. Other parasitic elements shorter than the dipole may be added in front of the dipole and are referred to as directors.
Why the input resistance of an op-amp is high whereas it's output resistance is low ?
Loading at the input point and to pass the maximum output to the load is the requirement of Op-Amp which is a current exchange device from input side to output side.
What do you understand by microwaves? Why these are called micro?
Micro waves are those waves whose wavelength is less than a foot(30 cms) or freq ranging from 1 GHz to 1000 GHz. Because of there tinyness these are called micro.
How do microwave oven works?
Heart of microwave oven is magnatron which generates frequency of appox. 2.4 GHz. Explain working of magnatron.
What is CMRR? Explain briefly.
CMRR stands for common mode rejection ratio. It is a measure of the ability of a test instrument to reject interference that is common to both of its measurement input terminals. It is expressed in decibels and it is the ratio of the actual or common signal level appearing on the two input terminals together to the measured level.
What is meant by D-FF ?
D Flip Flop The D ?ip-?op is the most common flip-flop in use today. It is better known as delay flip-flop or data latch.
What do you mean by an ideal voltage source ?
In electric circuit theory, an ideal voltage source is a circuit element where the voltage across it is independent of the current through it. Sources infinite current to any load without any change in o/p voltage.