Field strength / receive power converter

This little converter transforms a selected specification of field strength or received power to the other.

This calculator assumes a point source and plane wave conditions. Plane wave conditions do not apply very close to the source.

Calculated Antenna Factor assumes lossless transformation to 50Ω, irrespective of the specified receiver input resistance.

Example 1: calculate the noise power in a 2000Hz wide receiver at 7MHz with a -1dBi antenna at 1000m distance from the source, if the broadband source has a field strength of 30μV/m in 9000Hz bandwidth at 30m distance from the source (FCC 15.209 limit). Answer: -103dBm (S4 in S-meter terms, and well above expected lowest ambient noise).

Example 2: if the noise power in a 2500Hz wide receiver at 7MHz with a -1dBi antenna is -53dBm (~S9+20dB), what is the field strength of a broadband source in 9000Hz bandwidth in dBμV/m? Answer: 47.7dBμV/m (hint: use the same distance to source for both Field Strength and Receiver, the value doesn't matter, so long as it is greater than zero).

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