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One trick I've used? is to see how hot a 50 ohm resistor gets,
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Compare that to how hot a resistor on a variable voltage DC supply gets, vary the voltage till the heating is about the same then compute watts from V*V/R A diode RF probe is trivial to build, though involves a wee bit more math to interpret properly.. V*V/R = Watts, so V*V=Watts*R, and five watts into 50 ohms is sqrt(Watts*50ohms) = sqrt(5*50) = 15.8 volts rms. If the RF probe is peak reading, you will see 15.8 * 1.414 = 22.4 volts peak into a DC voltmeter. Many RF probe designs include a 4.7meg scaling resistor so it reads rms? on the assumption that the RF is a sine wave and the DVM has an input resistance of around 10meg. Those are some very large assumptions, I prefer to have it honestly tell me the peak voltage. Let's assume a 1n4148 diode has a forward drop of about 0.6 volts, a schottky Bat54s a drop of 0.2 volts. So errors get beyond 10% if below 6v peak for the 1n4148, or (6/1.414)*(6/1.414)/50 = 0.35 Watts. And errors get beyond 10% if below 2v peak for a Bat54s, or (2/1.414)*(2/1.414)/50 = 0.04 Watts. Taking that diode drop into account, the Bat54s can give useful results to well under a milliwatt. If you want an SWR meter that also shows power, consider Diz's $12 Tandem Match kit: ? ?? Item 18:?? If you want a full antenna analyzer, consider the nanoVNA and it's newer variants, as cheap as $40: ? ??/g/nanovna-users/messages?expanded=1 A steep learning curve, but very powerful. Jerry, KE7ER On Thu, Jan 9, 2020 at 01:50 PM, Alex Netherton wrote:
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