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Emergency Power Problems on the Power Grid
Published in Michael F. Hordeski, Emergency and Backup Power Sources:, 2020
Facilities with generators should run them for one to four hours under load quarterly as part of a regular maintenance program. A dummy load can be created by connecting a generator to a resistive load bank (an electrical unit load with resistors). Allow the water and oil temperatures to stabilize, then monitor performance over the testing time.
Testing Coaxial Transmission Line
Published in Jerry C. Whitaker, The RF Transmission Systems Handbook, 2017
The facility’s dummy load must next be matched to the transmission line. Do not assume that the dummy load is an appropriate termination by itself, or a station reference. The primary function of a dummy load is to dissipate power in a manner that allows easy measurement. It is neither a calibration standard nor a reference. Experience proves it is necessary to match dummy and transmission line sections to maintain a good reference. The load is matched by looking into the transmission line at the patch panel (or other appropriate point). Measurements are then taken at locations progressively closer to the transmitter, until the last measurement is made at the output connection of the transmitter. After the dummy load is checked, it serves as a termination.
From launch to transmission: satellite communication theory and SNG
Published in Jonathan Higgins, Satellite Newsgathering, 2012
A dummy load is a device that will absorb most of the power from the HPAs safely, and enables the uplink to be tested at full power as if it was transmitting to the satellite. The huge amounts of energy are dissipated as heat, and it is a routine procedure to test the uplink by running it up to full transmit power into the dummy load. Because of the small amount of leakage of the antenna, it should be ‘skyed’ (pointed in the opposite azimuth to the geostationary arc – North when in the Northern Hemisphere and South in the Southern Hemisphere) with no risk of directing the small leakage power toward people.
High-power shortwave DRM transmitter in solid-state technology
Published in Automatika, 2018
Goran Pavlakovic, Silvio Hrabar
The transmitter output was then connected to a dummy load and tuned. Voltage and current waveforms at PA module output were measured and can be seen in Figures 23 and 24. Higher operating frequency currents show the existence of not only the carrier frequency but also harmonic components that are caused by the non-ideal behaviour of the RF output stage elements. These harmonic components produce additional power dissipation in the RF output stage components. Measured RF system efficiency, ratio of average RF output power and PA modules input DC power, for RF carrier conditions without modulation applied, was from 65 to 75% depending on the frequency (smaller value for higher operating frequencies). With AM modulation applied, values from 70% to 80% were measured. In DRM mode, RF system efficiency values of 55–65% were measured. Observing the RF circuit, power is being dissipated mainly in the transistors due to switching losses, in the combiner transformer cores, and in lesser amount in the RF output stage inductors, capacitors and copper conductors. Overall transmitter efficiency, ratio of average RF output power and input AC power that includes all transmitter losses and auxiliary systems consumption, was found to be in the range from 60% to 70% in AM mode, 50–60% in DRM mode.
Low-cost leaky feeder communication for mines rescue
Published in Mining Technology, 2020
Michael D. Bedford, Angel J. A. Rodríguez López, Patrick J. Foster
The transmitter was a Yaesu FT-857D amateur radio transceiver. It was configured to transmit a CW (continuous) signal with an output power of 5W. The cable was hard wired to the transmitter and the end of the cable distant from the transmitter was terminated with a 75 ohm ‘dummy load’ resistor, this being the characteristic impedance of the cables. This corresponds to normal practice with leaky feeders, and is necessary to provide an acceptable match between the transmitter and the cable. The receiver was an Aeroflex 9103 spectrum analyser which was used with a 1.5 m whip antenna in a vertical configuration. The effective noise floor of this configuration, taking into account background noise, varied from −65 dB at 7 MHz to −73 dB at 144 MHz.
Design and implementation of a versatile H-bridge power supply for experiments on the STOR-M Tokamak
Published in Radiation Effects and Defects in Solids, 2023
H. Bsharat, M. Patterson, C. Xiao
The bipolar biasing H-bridge power supply was initially tested using a 5Ω dummy load. Figure 12 shows the measured waveforms of current through and voltage across the dummy load when the capacitor bank was charged to 100 V. The current was measured with a Pearson probe and the voltage was measured using a floating oscilloscope. Three positive and three negative pulses were generated. Calculation shows that the total charge delivered from the capacitor bank is much smaller than the total charge stored initially on the capacitor bank. Therefore, the bank voltage remains almost constant for the test. As expected, the amplitude of the negative pulses is larger than the positive pulses.