Measurement of Power Transmission Lines: When power is applied to Measurement of Power Transmission Lines, the source to load impedance must be matched in its characteristics impedance (Z0). The impedance all along the line is equal to the characteristic impedance. Therefore, the transmission line is said to be correctly terminated. Hence no reflection or standing […]
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Heat Capacity of Calorimeter: Heat Capacity of Calorimeter – RF power may be directly converted into heat. Water acts as the load, and RF power may be used to heat an element such as a long transmission line, water being used as a coolant. The RF power may be absorbed directly in the calorimeter fluid.
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Bolometer: Bolometric measurements are based on the dissipation of RF power in a small temperature sensitive resistive element, called a Bolometer. This bolometer may be a short ultra thin wire having a positive temperature coefficient (PTC) of resistance, called Baretter, or a bead of semi-conductor having a negative temperature coefficient (NTC) called Thermistor. Both Baretters
Precision Frequency Standard: Most high precision frequency standard in use utilise a geometric transverse (GT) cut quartz crystal as the frequency controlling resonant elements having changes in frequency of less than 1 part in 10 million per day. This GT quartz has the outstanding characteristic of exhibiting little variation in frequency over a temperature range
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Primary Standard: Primary Standard – One arrangement is a carefully designed quartz crystal oscillator operating in the range 50 to 100 kHz, having a low temperature coefficient, constant amplitude output and voltage regulated power supply. The crystal oscillator has a long time (several months) frequency stability of a few parts in a 100 million, without
Modem Definition: The term Modem Definition is an acronym for modulator-demodulator. The primary modem function is to convert digital data into an analog form which is suitable for transmission on common carrier circuits (example telephone lines). Modulation is the D/A conversion in which the digital data is placed on the transmission line by modulation of
Pulse Wave Code Format: There are many different code formats of pulse wave. The classification is based on three criteria, namely, form of information transmission, relation to zero level, and direction. Based on the form of information transmission, the format used can be any one of the following Full binary transmission, where both 0 and
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Delta Modulation(DM): Delta modulation(DM) is process of modulation in which train of fixed width pulses is transmitted. Their polarity indicates whether the demodulator output should rise or fall at each pulse. The input is caused to rise or fall by a fixed step height at each pulse. Figure 18.20 shows the block diagram of a
Pulse Code Modulation(PCM): Pulse Code Modulation(PCM) is different from the other forms of pulse modulation studied so far, PCM also uses sampling techniques, but it differs from the others in that it is a digital process. Instead of sending a pulse train capable of continuously varying one of the parameters, the PCM generator produces a
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Pulse Position Modulation(PPM): In this Pulse Position Modulation system, the amplitude and width of pulses is kept constant, while the position of each pulse, in relation to the position of a recurrent reference pulse, is varied by each instantaneous sampled value of the modulating wave. PPM may be obtained very simply from PWM, as shown
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