Attenuator Calculator

Version 1.0 27 April 2015

Summary

This is a special purpose calculator for the design of passive resistive attenuators

Instructions

The widget can perform single calculations and (in some cases) generate tables for later use.

Single calculations may be performed for both symmetrical (equal source and load impedances) and asymmetrical attenuators. Tables may be generated only for symmetrical attenuators.

In the asymmetrical case, the gain may not exceed a critical value which the calculator will indicate if the critical value is exceeded. At the critical gain, both T- and PI-networks reduce to L-networks.

Users should enter the source and load impedances to be matched, the input power and the gain required. The last can be entered as a power ratio in the range 0 to 1, or in decibels, expressed as a negative number. The widget then calculates the output power and the values of the two, three or four resistors that are needed to construct the attenuator.

The widget displays a schematic of the attenuator and specifications of the resistors. The schematic or the data can be copied to the clipboard using the normal browser methods.

In the case of a PI-Network or a T-Network:

In the case of a B-Network or a BT-Network:

Modes of Operation

The widget has eleven modes of operation which can be chosen by clicking on the Calculation Mode menu button.

The user may choose to do a PI-, T-, BT-, B-, L-, LS-, or LL-network calculation, or generate a table for a symmetrical network. In the latter case, the widget computes a table which covers a range of attenuation values from 1 to 50 dB. The table is displayed in a new window.

Input Units

Powers can be entered and displayed in watts, or in decibels referenced to 1 W (dBW) or 1 mW (dBmW).

In the case of L-network attenuators, the user must specify the source and load impedances to be matched and the input power. The widget then calculates the output power and the values of the two resistors that are needed to construct the attenuator.The maximum gain value (minimum attenuation value) is calculated by the widget.

In the case of LS-network attenuators, the user must also specify the gain required. The network matches the source impedance. In general, the load impedance will not be correctly matched.

In the case of LL-network attenuators, the user must also specify the gain required. The network matches the load impedance. In general, the source impedance will not be correctly matched and the gain of the network will not match the specified gain exactly.

License

The Attenuator Calculator is Copyright © 2013,2015 Harry Whitfield (G6AUC).

This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA

Widget Concept, Coding and Documentation

Harry Whitfield (G6AUC)