Monday, March 19, 2018

RF Probe for DVM

So many projects and the list is growing. How can you do RF work without a scope? Maybe a good RF meter would be a reasonable substitute. Even my cheap DVM has a 200mv DC scale. With a RF detector built into a probe this becomes a sensitive RF meter. If you rectify an AC signal and send the signal to a DC meter you read peak. RMS is .707 peak so the 200mv DC is about 140mv RMS. For signal tracing and checking to see if a circuit is oscillating you just need a relative reading. So the last project added to the list is one of these.
Or one of these.

As always the project is open to modification. Either of these two would be a good start. Ummm? I had a TV antenna come apart when the tree hit it in one of the hurricanes. I saved that aluminum tubing for just such an occasion as this.
A little tubing, a finishing nail filed to a point, a diode, capacitor and resistor. Need two to check an amp input and output. Using the same meter and probe will give a relative reading that could be used to determine gain. You could use a signal generator and 'calibrate' the meter against it.

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