Calculator to support Manual Testing of Field-Strength Levels Using Conventional Receivers

This is a simple calculator to support the technique described by Ed Hare of the ARRL in "Manual Testing of Field-Strength Levels Using Conventional Receivers" and should be used in conjunction with that document. The field names used in this calculator are those described in the reference document.


Receiver Bandwidth (Hz) Receiver noise floor  (dBm)
Attenuator (dB) Additional loss (dB)
Frequency (MHz) Antenna gain (dBi)
Vterminated (mV) Vmeasured (mV)

Example 1: An IC706IIG with an effective noise bandwidth of 1900Hz and Noise Figure of 6dB is used to measure field strength at 7.1MHz with an antenna of gain -1dBi, additional cable loss of 0.4dB and a 30dB attenuator. Using the Receiver sensitivity metric converter, the receiver noise floor is found to be -135.2dBm. Vterminated is 85mV and Vmeasured is 125mV. Calculated field strength is -8.9dBμV/m, normalised field strength (1Hz) is -41.7dBμV/m.

Additional resources:

The algorithm in Ed's paper is an approximation that is valid where the external noise is large compared to the noise power in the termination (which usually applies over most of HF), and is convenient for hand calculation. The Improved button executes the more accurate algorithm.

If you're clever, you will have worked out you can download this page to your hard disk. If you're smart, you won't, you will run it from the web site and automatically take advantage of any updates.

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© Copyright: Owen Duffy 1995, 2021. All rights reserved. Disclaimer.