RF Circuit Assistant

Written by Shane Feek (KC8BRO) © 20th June 2008 & October 2, 2009.

What is RF Circuit Assistant?
RF Circuit Assistant is a small program written using the .NET 3.5 framework that allows one to perform many of  the calculations necessary for designing both transistor and tube based receivers and transmitters. It was created with an emphasis on ease of use, and provides a unique "table" based output form for many of its calculators. Each calculator is implemented on an individual form which allows for the testing of many "what if" scenarios simultaneously. RF Circuit Assistant makes it easy to find matching parts for existing "Junk Box" components to create useful circuits quickly.

Installation and System Requirements
Installing RF Circuit Assistant is easy! Simply unzip the files into a temporary directory and double click the Setup.exe file. If you do not already have .NET framework 3.5 installed, the program will give you the opportunity to download and install it during the setup process. If the .NET framework 3.5 fails to download or install during the Setup process, simply go to http://microsoft.com/downloads to download and install the .NET framework 3.5 (dotNetFx35setup.exe) file prior to running the RF Circuit Assistant Setup.exe. The program should show up in your Start Menu under the Geek’s Haven Lab folder.

The system requirements are as follows: Windows XP SP2 or higher and .NET Framework 3.5.

The Calculators

Turns -> Inductance (Torroid)

This calculator allows you to enter the Al (or turns per 100 uH) value of a ferrite torroid and a specified number of turns. Its output is a table of all of the Inductance values from 1 to #Turns in 1 turn increments. This assumes that all turns are uniformly spaced and wound in a single layer.

Turns -> Inductance (Air Core)

This calculator allows you to enter the coil diameter in mm, wire width (or thickness) in mm, and a specified number of turns. Its output is a table of all of the Inductance values from 1 to #Turns in 1 turn increments. This assumes that all turns are close wound in a single layer with enamel coated wire.

Capacitance -> Frequency

This calculator allows you to enter an Inductance in uH, Starting Capacitance in pF, Ending Capacitance in pF, and a Capacitance Step in pF. Its output is a table of resonant frequencies based on the inductance entered and the indicated capacitance for a parallel tank circuit. To calculate just one value, simply enter the Inductance and Starting Capacitance then click Calculate.

Inductance -> Frequency

This calculator allows you to enter a Capacitance in pF, Starting Inductance in uH, Ending Inductance in uH, and an Inductance Step in uH. Its output is a table of resonant frequencies based on the capacitance entered and the indicated inductance for a parallel tank circuit. To calculate just one value, simply enter the Capacitance and Starting Inductance then click Calculate.

Capacitive Reactance @ Frequency

This calculator allows you to enter a Frequency in MHz, Starting Capacitance in pF, Ending Capacitance in pF, and a Capacitance Step in pF. Its output is a table of reactance values in Ohms for the corresponding capacitance value. To calculate just one value, simply enter the Frequency and Starting Capacitance then click Calculate.

Inductive Reactance @ Frequency

This calculator allows you to enter a Frequency in MHz, Starting Inductance in uH, Ending Inductance in  uH, and an Inductance Step in uH. Its output is a table of reactance values in Ohms for the corresponding inductance value. To calculate just one value, simply enter the Frequency and Starting Inductance then click Calculate.

Capacitors Inductors Resistors

This multifunction calculator allows the computation of resistors, inductors, and capacitors in both series and parallel configurations. Simply enter the resistance, inductance, or capacitance in the appropriate box and click Enter. Each time another value is entered, the total for that box is updated. An infinite number of component values can be entered in each box. To reset a particular calculator box just click the appropriate Clear button.

Variable Capacitor Scaling

This calculator allows you to enter the Starting Capacitance in pF, Ending Capacitance in pF, the Variable Capacitor Starting Capacitance in pF, and the Variable Capacitor Ending Capacitance in pF. Its output is the required series and parallel capacitance values in pF (connected according to the diagram) necessary to transform the variable capacitor’s adjustment range to the indicated capacitance range. Note that the adjustment range of the variable capacitor must be sufficient to span the entire output capacitance range.

Transmitter Output Matching

This calculator allows you to enter the desired TX Output Power in W, Peak-to-Peak Collector or Plate Voltage in V, TX Output Resistance in Ohms, TX Center Frequency in MHZ, the Unloaded Q of the Matching Coil, and a Phase Shift in Degrees. The output contains the component values required for the match as well as their reactances. Also included are the resulting Input and Output Resistances, the Loaded Q of the entire PI network, the bandwidth of the 3dB power loss points, the overall Efficiency, and the amount of power lost in the matching coil.

Impedance Matching

This calculator allows you to enter the desired Input Resistance in (Ohms), Output Resistance in Ohms, Center Frequency in MHz, the Unloaded Q of the Matching Coil, and a Phase Shift in Degrees. The output contains the component values required for the match as well as their reactances. Also included are the resulting Input and Output Resistances, the Loaded Q of the entire PI network, the bandwidth of the 3dB power loss points, and the overall Efficiency.

Coax Stub Notch & Pass

This calculator allows you to enter a Frequency in MHz and a coax cable Velocity Factor. Its output is the length (not including the connector) of the required stub in cm. For a “Notch” filter stub, leave the coax open at the end. For a "Pass" filter stub, short the coax at the end.

Read the RF Circuit Assistant License Agreement

Download and Install the Most-Recent Version of RF Circuit Assistant
Download and unzip rf-circuit-assistant.zip Version 2.05. Uninstall any previously installed version, then unzip the downloaded zip file and run setup.exe to install the program.