Efficiency Calculator
for QRP Small Loop Antennas


    This is the download page for a calculator of the efficiency of QRP small loop antennas. The calculator is based on the bandwidth method described by A. Findling, K9CHP, and K. Siwiak, KE4PT, in The QRP Quarterly. [1]

   The page you are reading is a supplement to an article on this web site,  “Measuring the Efficiency of a QRP Small Loop Antenna”, which includes a summary of the bandwidth method and examples.

   The inputs for the calculator include the unloaded, -3 dB bandwidth that you measure with an antenna analyzer as explained in Ref. 1 and on a separate page. The calculator doubles the unloaded bandwidth to arrive at the loaded bandwidth and the loaded Q factor. You can scroll to the second page of the spreadsheet to see the formulas and intermediate results.

   Here is a screenshot of the calculator:


   To use the calculator you will need the free LibreOffice Calc spreadsheet program (Windows, Mac OS, and Linux) or Excel.

Download Links


English units:

   Libre Office LoopCalc-v1.0 (.ods)

   Excel 2007–2013 XML LoopCalc-v1.0 (.xlxs)*


   Libre Office Metric-LoopCalc-v1.0 (.ods)

   Excel 2007-2013 XML Metric-LoopCalc-v1.0 (.xlxs)*

*The Excel version was formatted by LibreOffice Calc. Before it opens in Excel a format alert is displayed, and then it runs properly.


1. A. Findling and K. Siwiak, “How Efficient Is Your QRP Small Loop?” The QRP Quarterly, Summer,2012, pp 22-23.




Author Information

   Peter DeNeef, AE7PD, is an Extra Class amateur radio operator in the U.S.  This Web site has no ads or conflicts of interest.
Email:  HamRadioAndVision "at" gmail "dot" com.

Measuring the Efficiency of a QRP Small Loop Antenna

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rev. 8/21/2016