Building the QRPometer

One thing that all QRPers  seem interested in is just how much (or is it little?) power their rigs put out. I am no exception. You see, QRP is all about making contact with someone using as little power as possible.

Until now, the way I have worked out how much power I am using is by using a great piece of kit produced by Doug Hendricks called the Dummy Load/Power Meter, It requires you to make use of a mathematical formula to compute your output power.

Recently the Four State QRP Group produced a fabulous piece of gear they call the QRPometer. This is an inexpensive, highly accurate VSWR and Power Meter for QRP levels. They say it permits the testing of a QRP transmitter to an accuracy of 2% or better from 100 mW to over 10W. It also has a resistive bridge type circuit which inerts 6 dB of attenuation between the rig and the antenna for tune up purposes. This is great, especially if your rig has no VSWR protection.

The kit came beautifully packed and sorted into component groups. All components were there, something that isn’t all that common these days.

The components as unpacked.

The instructions were easy to follow and it took me about 4 hours to complete. Calibration was super simple, requiring a trim pot to be adjusted until a voltage reading of 5V was obtained on a digital multimeter. Once that was done, an RF signal from a QRP rig was inserted and the calibration pot on the back of the display was adjusted until a reading of 1.00 was obtained. That was all there was to it. Simple.

An interesting aspect to this kit is that the two PCBs fit together to form the enclosure.

The two PCBs ready to be connected together to form the enclosure.

The kit came with the necessary hardware to secure the two boards together.

The completed QRPometer with the two boards screwed together to form a nice looking enclosure.

So how does it perform?

Using my DC40A 1W transmitter, I got a reading of 900mW at 13.8v supply. This computes well compared to the mathematical method in which I got 942mW.

My DC40A rig is putting out 900mW.

Power levels for my two RockMites are as follows:

RM80 = 460mW at 13.8v

RM20 = 330mW at 13.8v

Turning now to my PFR-3 rig, these are the readings I obtained for the three operational bands:

20m = 5.29W

30m = 4.70W

40m = 5.11W

So now I have an accurate indication of just how much my QRP rigs put out.

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3 thoughts on “Building the QRPometer

  1. I recently built one of these. The only problem I found was getting the 3 pins of the voltage regulator into holes in the green circuit board: they were too large! There’s a fix on the website, by the way. For the money (about 50 UK Sterling by the time VAT and other fees were included) it’s a remarkable bargain.

    I’ve been using it as an RF probe on a WSPR beacon kit which I built recently. I’ve also used it to calibrate the QRP range on my Elecraft K2 – it was way off!

    Bob
    MM0RKT

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