Simple RF Probe

The RF Probe is one of the handiest accessories you can have when you are working with RF and transmitters. This probe may rank as one of the simplest and cheapest project. It uses only 3 electronic components. When used with a high-impedance DC Voltmeter, it can be used to measure RF voltage (and power), trace RF signals in a new design, and troubleshoot malfunctioning RF circuits.

This RF Probe is used in conjunction with a high-impedance-input Voltmeter or Digital Voltmeter (DVM). With a 1-Meg DVM, it reads 25% of the sinusoidal RMS voltage. Reasonable accuracy (+/- 10%) can be expected over the HF/VHF range (2-150 MHz), although this hasn't been verified.

The RF probe can also used to measure RF power with reasonable accuracy, up to about 50 watts in a 50-ohm circuit. By 50-ohm circuit, I mean a 50-ohm antenna system at 1:1 SWR (higher SWRs are not 50 ohms), or a 50-ohm dummy load. Assuming the resistor in your RF probe is sized to match your DC Voltmeter's input impedance.

Source: Classic RF Probe
Read more: Radio Spectrum