A useful tool that can be easily crafted out from your junk box is this rf voltmeter. I discovered this circuit online and created a prototype out of it. I found this project very useful in reading RMS voltage in my HF /VHF projects. I use it to determine the output power of my rf amplifier, set the null in my balanced modulator, determining the peak voltage output of my oscillator, peaking a band pass filter, etc...
It takes only 3 components to start with. I use 1N60 germanium diode to rectify the high-frequency AC signal into a DC voltage compatible with any digital multimeter. My prototype rf voltmeter is mounted in a small PCB assembled in surface mount fashion. Two connectors soldered on the edge of the pc board to accommodate the positive and negative probe of my digital multimeter.
Connect the alligator clip to the common ground of the circuit you are measuring. Minimize the length of the alligator clip wire to avoid introduction of errors in your measurements, particularly on higher hf bands. In my prototype the lead wire for the alligator clip is just over 6 inches.
When reading the Vrms, take the measurement across the 50 ohm dummy load. For instance, if you measure 13V using your digital tester, the computed power is around 3.38watts, calculated using the formula P = (Vmeasured)² / 50. ---73 de du1vss
