Several of the more common RF calculations are presented here in the form of online calculators.
Note that the results given by these calculators should be considered as estimates, and not the absolute truth. In practice, many factors can affect RF link performance, some of which are described here.
Transmitter power is generally specified in terms of Watts, or mW (milliWatts), but RF calculations generally require power in terms of dBm (dB relative to a milliWatt).
| Power in mW |
| Power in dBm |
The loss in signal strength of an electromagnetic wave as it passes through free space. Measured as a line-of-sight path, with no reflections, or diffraction.
This is the effect that causes shorter range on higher frequencies in FPV links.
| Frequency in GHz |
| Distance (km) |
| Path Loss |
The estimated range of a line-of-sight RF link, given the transmitter power, transmitter and receiver antenna gains, receiver sensitivty, and the link margin.
This calculation should be considered a best-case number, other effects can significantly reduce this range.
| Frequency | GHz | |
| Tx Power | dBm | |
| Rx Antenna Gain | dBi | |
| Tx Antenna Gain | dBi | |
| Link Margin | dB | |
| Rx Sensitivity | dBm | |
| Range (km) | km |
A simple, but quite useful calculator, to determine how many times further your RF link can go given a number of dB increase (or decrease) in power.
As an example, your 500mW (27dB) transmitter is putting out 1dB less than it should (26dBm, or 400mW), what effect does that have on range?
Answer: 0.89 times, or 90% of the specified range
As another example, what kind of range increase should you expect if you increase your antenna gain by 11dB (e.g. upgrading from a SpiroNET Omni to a SpiroNET 13dBi patch antenna)?
Answer: 3.55 times, so if your range was 1km before, it will now be closer 3.55km
| Power increase (decrease) in dB |
| Times further |
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