Found 1006 Articles for Electronics & Electrical

In this section, we will solve some problems on wireless channel noise based on the white noise model.Example Problem 1A white noise has a 2-sided power spectral density of 6 kW/MHz. It is passed through a low pass filter having a bandwidth of 1 kHz. Compute the output noise power.Solution −The 2-sided power spectral density is 6 kW/MHz. The power spectral density is usually represented in W/Hz.$$\frac{6kW}{MHz}=\frac{6000W}{1000000Hz}=\frac{0.006W}{Hz}=\frac{N_{0}}{2}$$The 2-sided power spectral density N0/2 is 0.006W/Hz. Therefore, N0 = 0.012W/Hz.The noise power is expressed as the product of the noise power spectral density and the noise bandwidth.$$N_{p}=N_{0}.BW$$$$N_{p}=\frac{0.012W}{Hz}.1kHz=12W$$The noise power of the given ... Read More

What is Wireless Channel Noise?It is not possible to have any wireless communication system/link with absolutely zero noise level. Noise is additive and hence at the receiver, we have the signal that contains both the transmitted data and noise. The most commonly used noise model is the Additive White Gaussian Noise (AWGN). The noise follows Gaussian distribution with zero mean.What are the effects of channel noise?The channel noise could distort the original user data signal.If the channel noise is too high, it will bring down the Signal-to-Noise Ratio (SNR) of the signal as a result of which the receiver might not be ... Read More

Let us look at some numerical on amplifiers to get a better grip of the theoretical understanding.The ratio of output to input voltage of an amplifier is 20. Compute the voltage gain.Solution − The voltage ratio is given as 20. We need to convert this linear ratio into logarithmic ratio to arrive at the solution.$$Voltage\:gain(dB)=20log_{10}(20)\sim\:26dB$$The positive voltage gain indicates that the output power is greater than the input power.What does amplification in power by 3 dB indicate?Solution − Let the output power be ‘y’ and input power be ‘x’. Representing this as an equation, we have$$3dB=10log_{10}(\frac{y}{x})$$$$log_{10}(\frac{y}{x})=0.3dB\Rightarrow\:\frac{y}{x}=10^{0.3}\sim\:2$$Thus, the output power is twice the ... Read More

Function of AmplifiersAmplifiers boost up or amplify weak signals. Repeaters are good examples of amplifying devices. They are present in few to several numbers at intermediate points between the transmitter and receiver, depending on the actual distance between the two. Periodic amplification at intermediate stations between the transmitter and receiver ensures that there is a desired level of signal-to-noise ratio (SNR) maintained with the signal to successfully complete the final mile of transmission.Understanding Amplifier GainsExample 1If in a two-amplifier system where the amplifiers are cascaded in series, the first amplifier provides a gain of 10 dB while the second amplifier ... Read More

Problem 1 on Power LevelFor a communication link, the received power level is measured as 5 dBm. What does this mean?Here, we have a positive ‘dBm’ and hence we can say that the received power level is greater than the reference power level which is 1 mW.$$5dBm=10log_{10}(\frac{P_{received}}{1mW})$$$$log_{10}(\frac{P_{received}}{1mW})=\frac{5}{10}=0.5$$$$(\frac{P_{received}}{1mW})=10^{0.5}=3.1622$$$$P_{received}=3.1622mW$$We can infer that the received power level is 3.1622 times greater than the reference power level. However, this doesn’t mean that the received power level is greater than the input or transmitted power level. In fact, the received power level can never be greater than the transmitter power. In practice, the received power ... Read More

In wireless communication, the magnitudes of certain parameters such as power and voltage vary over several orders- for example; the received signal power level in mobile communications can vary between tenths of a milli-watt to about a few hundred of a milli-watt. For certain wireless communication systems, the received power can vary between a few tens of a watt up to few tenths of a microwatt! This is due to the wireless channel conditions in the form of noise, fading and so on.The following equations represent the voltage and power gains with reference to 1 V and 1 W respectively.$$Voltage\:gain(dBV)=20log_{10}(\frac{Voltage\:Value}{1V})$$$$Power\:gain(dBV)=10log_{10}(\frac{Power\:Value}{1W})$$Since ... Read More

dBW, dBV, dBmW, dBµW, dBmV and dBµVLet us see some commonly used decibel based representation units in wireless communications. The difference between these entities lies in the type of ratio and the reference levels of the quantities. We can have power ratio, voltage ratio, current ratio, and so on. Reference levels can be 1 W, 1 V, 1 mW (milli-watt), 1 mV (milli-volt), 1 µW (microwatt), 1 µV (microvolt), and so on.Voltage based dB representation unitsThe ratio of two voltages will be mapped on to the decibel scale. Often, one of the two quantities of the ratio is a reference ... Read More

Valid and Invalid Operations on dBSome of the valid operations that can be performed with ‘dB' is discussed in this article. When we add ‘dB’ to a quantity, we are increasing its value and when we are subtracting ‘dB’ from a quantity, we are reducing its value.We can add ‘dB’ to ‘dBm’ but not ‘dBm’ to ‘dBm’.37 dBW + 3 dB gives 40 dBW. However, 37 dBm + 37 dBm doesn’t yield 74 dBm. This is an invalid operation.$$37\:dBm=10log_{10}(\frac{P_{out}}{1mW})$$$$log_{10}(\frac{P_{out}}{1mW})=3.7;\:P_{out}\sim\:10^{3.7}mW\sim\:5W$$Also, 74 dBm ≈ 25 MW. When we add 37 dBm to 37 dBm, all we get is around 10 kW, which ... Read More

Introduction to dB OperationsThe ‘decibel’ is a form of representing ratios on a logarithmic scale instead of linear scale. They are used across several disciplines of STEM. In this article, we will see how to perform calculations using decibels with examples pertaining to electrical engineering. We know that the ‘decibel’ represents the ratio of two quantities on the logarithmic scale. While comparing two quantities, one of them will be considered as a reference. This article discusses the basic operations that could be performed on decibels with some examples.Basic operations based on logarithmsLogarithmic MultiplicationThe logarithm of the product of two numbers ... Read More

What are the applications of decibel (dB) representations?For convenient representation of data for analysis, the decibel representation is used for various parameters such as amplifier gain, return loss, path loss, signal-to-noise ratio (SNR) and so on. Some of such representations are presented here.Quantity in decibel (dB) = log10(Compared Quantity)/(Reference Quantity)Amplifier GainRF (Radio Frequency) power amplifier gains are also usually expressed in ‘dB’. It is a practice to arrange amplifiers in series to achieve high gain at the output. This form of arrangement is called cascading. In a cascaded amplifier system, the output of one amplifier is fed as input to ... Read More