The WM-2 QRP Wattmeter from Oak Hills Research

The WM-2 from Oak Hills Research is a cool QRP wattmeter kit, which can measure forward and reflected power in three ranges: 100mW, 1W and 10W. With an accuracy of 5% of the full scale it should be possible to measure powers down to 5mW using this instrument. The WM-2 has a big, easy to read scale and can operate either from a built-in 9V battery or an external DC source.

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OHR WM-2 Alignment

Now that my OHW WM-2 is assembled, it is time to align it. The manual has detailed step by step instructions on this as well and the alignment procedure is relatively straight forward. On the other hand, adjusting the potentiometers can be a little difficult, partly because some of them are hidden below the wires and partly because R6 has to be adjusted with a precision of 1 mV while it has a full scale of several volts. It would have been very nice with a multi-turn potentiometer instead.

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OHR WM-2 Progress Report 3

I’m continuing with the connectors switches and the instruments. I don’t quite understand why the assembly manual wants me to use the bottom row on the power switch instead of the top row. The switch is already mounted on the cabinet and thus the bottom row is much more difficult to access than the top row. I just ignore this step and use the top row.

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