HF Forward Power & Return Loss (SWR) Meter

This meter displays forward power, within about 10% or +/-0.4 dB, from 10 milliwatts(-20 dBw) to 300 watts(+24.8 dBW) on one scale. A second scale displays return loss, which is related to SWR, from 0 to 30 dB with as little as 1 milliwatt of forward power. Indicated return loss is essentially constant for forward power ranging from 1 milliwatt to 300 watts. It is no longer necessary to try to read SWR from the intersection point of two swinging needles! Maximum return loss indicates the lowest SWR.  Meter Scale

With the addition of an external DVM, forward and reflected power can be measured from 3 microwatts to 300 watts, which is equivalent to an 80 dB power range and extends its utility to the test bench as well. It's all done with two 8-pin DIPs, one 14-pin DIP, some resistors, capacitors, and a transformer.

To view or download an Adobe Acrobat PDF file that shows how to build this meter, click here. This article also appeared in "QRP Quarterly", Oct. 2002.

To download a copy of Adobe Acrobat Reader which is needed to view PDF files, click here.

Here is a standalone version that uses a meter with its unmodified 0-50 scale for both forward power in dBm and return loss in dB. 0 dBm is 1 milliwatt and +50 dBm is 100 watts. There are also some minor circuit modifications required that can be e-mailed to the interested reader.

Click to enlarge
(Click on pictures to enlarge.)
It runs on a single 9V battery that can be clipped on the back or an external +6 to +16 VDC power supply. Click to enlarge

Please feel free to contact me with any comments or questions at:


Paul Kiciak, N2PK

URL: http://n2pk.com/RLPmtr/RLPmeter.html
Last updated: 20 Oct. 2006
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