Introduction

The Chemandy calculators are designed to be easy to use and follow a common theme and layout where possible. Most of them have been used for several years now and complaints about their accuracy or functionality are very rare. We do welcome these however and there is a contact link on the bottom of every page for this purpose.

Instructions for use

Simply enter the characteristics required as a decimal number and hit the "Calculate" button. Couldn't be easier! If the answer given is NaN (not a number) then it is most likely that the number was not entered as a decimal or perhaps you used a comma instead of a full stop/period for the decimal point.

There are two basic methods of calculation used. The simple analysis type which will only calculate ideal component values and a more comprehensive type which can also work backwards from preferred component values giving a simulation of the circuit performance.

For instance you may require a 10 dB attenuator working in a 50 Ohm system. If you use the Pi Attenuator calculator with results for resistance, attenuation, return loss, VSWR and reflection coefficient the analysis will give you an ideal series resistor of 71.151 Ohms and an ideal shunt resistor of 96.247 Ohms. Neither of these values exist and a suitable value has to be selected. This may be from components that are to hand or maybe from the list of appropriate Preferred Resistor Values. The first time that the calculate button is used, the calculated ideal resistance values will be loaded into the preferred value (amber) text boxes as a starting point. It is now possible to change the preferred values to those available and calculate again. The calculator now simulates the circuit and gives the Attenuation, Input Impedance, Reflection Coefficient, VSWR and Return Loss for the preferred values entered. This makes it possible to select the component values for a particular characteristic i.e. most accurate attenuation or the best return loss.

Accessibility

The facility of selecting text boxes by use of the keyboard only has been added on some calculators and will eventually be added to all of them. The Key Letters are underlined in the text box label and can be selected on most browsers using Alt + Shift + Key Letter although Internet Explorer is a little easier because the Alt key does not have to be depressed. The Opera browser is a little different and first Shift + Esc has to be selected to get into the access key mode and then Alt + Shift + Key Letter can be used as per the other browsers. Text boxes can also be selected by left clicking the labels with the mouse. Further text boxes and the calculate button can be selected by stepping through the calculator using the tab key. Some users may find it is easier to use Sticky Keys or AccessX which makes all of the key presses sequential and so avoids multiple key presses.

Microstrip Calculator Accuracy

The different formulas used for the microstrip calculators give different results. Which gives the best absolute accuracy with different PCB types has not been assessed by us and the choice is yours. The following table compares bench mark values used by Polar Instruments with the results obtained with our calculators. They are based on a 1 oz copper track, ε_{r} at 4.2 and a 0.79375 mm substrate.

Track Width (mm) | Numerical Method Zo (Ohms) | IPC-2141 JavaScript Zo (Ohms) | Wadell JavaScript Zo (Ohms) | Hartley JavaScript Zo (Ohms) |

3.3 | 30.09 | 21.06 | 30.14 | 30.39 |

1.5 | 50.63 | 49.45 | 50.71 | 51.51 |

0.45 | 89.63 | 91.33 | 89.03 | 92.79 |

Coplanar Waveguide Calculator Accuracy

The results obtained from the Coplanar Waveguide calculators were compared to those of Sonnnet 3D. For all calculations, W = 3
mm and ε_{r} = 2.94.

Track Width
S (mm) |
Dielectric Thickness
h (mm) |
Sonnet 3D
Zo (Ohms) |
Chemandy Calculator
Zo (Ohms) |

10 | 10 | 67.6 | 65.8 |

10 | 20 | 73.8 | 71.8 |

10 | 30 | 75.2 | 73.1 |

10 | 40 | 75.5 | 73.6 |

10 | 50 | 76.0 | 73.9 |

20 | 10 | 49.1 | 47.8 |

20 | 20 | 58.1 | 56.7 |

20 | 30 | 60.7 | 59.2 |

20 | 40 | 61.8 | 60.3 |

20 | 50 | 62.3 | 60.8 |

20 | 60 | 62.5 | 61.1 |

Script Language

The original calculators used VBScript to perform the calculations. This was adequate when the majority of people used Internet Explorer but now Microsoft is dis-continuing the use of VBScript in their browsers. Virtually all modern browsers have JavaScript and this has now been adopted as the standard for our new calculators. All JavaScript calculators are tested for functionality and appearance using Explorer 11.0, Google Chrome 73.0, Mozilla Firefox 66.0.3 and Opera 58.0 browsers.