Calculates the resistor values, attenuation, minimum attenuation, impedance, reflection coefficient, VSWR and return loss of a resistive matching Pi attenuator.
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The required input and output impedance are used to calculate the minimum attenuation possible for correct impedance matching with a formula from RF Design Guide, Systems, Circuits and Equations by Peter Vizmuller Published by Artech House ISBN 0-89006-754-6
Where Zin is the systems characteristic input impedance and Zout the system characteristic output impedance
Peter Vizmuller also gives formulas for calculating the resistor values directly. This calculator uses formulas that have been derived and first finds the output voltage with a source EMF of 2 Volts and therefore an input PD of 1 Volt.
The individual ideal resistor values can now be found.
After selecting preferred values, simple series and parallel resistor calculations are used to find the attenuator input impedance, input voltage and output voltage. The source EMF is again assumed to be 2 Volts.
The remaining formulas for Attenuation, Voltage Reflection Coefficient and VSWR are available at:-
http://www.kathrein-scala.com/tech_bulletins/EngRef.pdf
Note: With the Mismatch Losses box ticked the calculator will return an attenuation calculated from the source power in relation to the attenuator output power which is suitable for calculations at RF and Microwave frequencies, particularly if the attenuator is located away from the source at the end of a transmission line. Without the Mismatch Losses box ticked the calculator will return an attenuation calculated from the actual input power to the attenuator in relation to the output power which is more suitable for calculations at audio frequencies. The difference in attenuation with the two methods is only noticeable when there is a significant mismatch.