FREQUENCY RESPONSE OF RESISTORS.
Program METALFLM.exe 41 Kbytes.
This program models small low-wattage wire-ended resistors including spiralled metal-film resistors. The model's equivalent circuit is a chain of T and L networks. Values of lumped inductance and stray capacitance are estimated by the program from the component's physical dimensions.
The component with it's terminating leads is treated as a lumped L and C non-uniform transmission line. The program computes input impedance from 10 KHz up to 5 GHz with the other end grounded. Fast and slow frequency sweeps are available to observe maxima and minima of Zin.
Max and min Zin are approximately related to the physical length of the component, including connecting leads, but occur at frequencies far higher than the usual and useful working frequency range.
The reflection cefficient and standing-wave-ratio are calculated with reference to Zo, Zo being the DC value of the resistor. The usefulness of the component as a dummy load or for other purposes at any frequency can then be ascertained.
The effectiveness versus frequency of solid carbon-rod resistors and multi-turn UHF chokes, which are of similar wire-end construction, can also be determined. Chokes can be wound over the bodies of high-value wire-ended resistors, the parallel resistance value perhaps having some desirable effect on the ultimate response.
Another use for resistors having a good high frequency response, or at least a known frequency response, is for ratio arms and switched resistors in impedance bridges and other measuring instruments.
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