20 august 2022

Home made HF PWR/SWR-meter - revisited

Three years ago I played with a Stockton Bridge and made (just because I had it on my shelf) a nice portable HF power meter and SWR meter with cross-needles.

In the first iteration, it was meant to work with QRP radios; it has an impressive 5-600 mW range but on a second thought, I though what if I can use it for a broader range.

And I put a double potentiometer to change the range. 

But that was not a reliable solution because the range was somehow too "variable" and I never knew the real power.

So, a new iteration was born.

The PWR and the SWR voltage came from the Stockton bridge to a set of 2 x 4 * 1 MOhm potentiometers that will set the range for each position on the switch.

The switch is a dual pole-4 position and the ranges will be 10 W, 50 W, 100W and 200 W.

The calibration was made with a NRP-Z11 power sensor. While it is not a very reliable measurement tool, it helps to see the approximative value of the average or CW power. The 10W scale is pretty precise but the others are not so good.
The values are consistent through 1.5 MHz - 80 MHz.

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