About decibench

Engineering calculators for people who have to make a link work in the field, not just describe it on a drawing.

Why this exists

There is no shortage of online calculators for network and RF work. There is a shortage of ones that get the hard parts right. Most are a single formula wrapped in a form, and they quietly skip the cases that actually bite you on site: the constraint that is not the one you were watching, the limit that has a minimum as well as a maximum, the component everyone forgets to count.

A worked example from the PoE calculator here. A powered device draws constant power, so the current depends on the voltage that survives the cable, which depends on the current. Calculators that use I = P / V under-report the drop. The honest answer needs the quadratic solved, and that is a few extra lines nobody writes because nobody checks.

From the PON calculator: every ITU-T ODN class is a window. Go below its minimum and the receiver overloads. It is a real failure on short drops behind a small splitter, and in the field it does not present as an optical budget problem at all — the power meter reads healthy, so people go hunting for a fault that is not there. Almost no budget calculator checks that end of the window.

How the tools are built

Every calculator here follows the same three rules.

The constants are shown, not hidden

Where a figure comes from a standard, the standard is named. Where it is a typical value rather than a specified one, it says so, and you can replace it with the number from your own datasheet. Splitter insertion loss is presented as the theoretical split plus the device's excess loss rather than as a single constant, so you can audit it rather than trust it.

Design values, not best-case values

The defaults are what you should budget against, not the prettiest number on a datasheet. Fibre attenuation figures are design maxima. The PoE calculator offers the TIA conductor resistance limit as an option precisely because the cable you are handed is rarely the cable in the brochure. A tool that flatters your design is worse than no tool.

Each tool ships with its own checks

The calculation behind every tool is a separate module with an executable test suite, and the strongest tests are the ones that reproduce the governing standard's own arithmetic. For PoE, at each type's worst-case operating point — minimum PSE voltage, maximum channel resistance, maximum current — the model has to land on the exact figures IEEE publishes for powered-device voltage and power. It does, to the decimal. If the equations were wrong, those numbers would not close.

What these tools are not

They are design aids, not a substitute for the standard, for the manufacturer's specifications, or for measurement. Every one of them states its own limitations on its page, and those sections are worth reading: they tell you what the model does not cover. On installed plant, a measured value beats a calculated one every time.

Nothing here is professional engineering certification. See the terms of use.

Corrections

If a figure here is wrong, or a tool misses a case that matters in the field, say so — that is the most useful message this site can receive. Working results, datasheets and standard references are all welcome. Write to [email protected].

Privacy, briefly

Every calculation runs in your browser. Nothing you type is transmitted, logged or stored anywhere. There are no accounts and no tracking. The privacy policy has the detail.