21 Aug Measure RF Voltages with a Multimeter
Bob Snyder
Engineer American Environments Company, Inc
It is possible to enable an ordinary multimeter to measure RF voltages with can prove very handy in many troubleshooting situations to measure RF voltage and power, trace unwanted EMI noise, and troubleshoot oscillator circuits.
The circuit is extremely simple to build and very inexpensive.
The diode is a high speed small signal Schottky type. Your basic silicon diodes will not work in this application. The Leads need to be kept as short as possible. The circuit can be housed in almost anything, but there is an advantage in shielding the probe.
The probe is very easy to use, but there a few things to keep in mind.
- Do not use the probe in a circuit where the DC supply voltage is greater than the diode’s reverse breakdown voltage.
- Do not measure the Peak RF power in a circuit where the peak voltage will exceed the rated value of the capacitors.
- Don’t reverse the polarity if the banana plug leads to the multimeter
- Plug the banana plug leads into the DC input of the multimeter.
In summation even though this circuit is merely a simple series detector it is a very useful piece of equipment to have in your arsenal of troubleshooting tricks.
Noel C
Posted at 22:58h, 09 SeptemberHi Bob
Nice little article, thank you!
Now I’m starting to build an impedance analyzer the difference between R and Z is becoming important!
When measuring an RF voltage across a complex impedance with a detector such as in your example
is the resultant voltage measurement derived from V = I x R or from V = I x Z ?
I hope my question makes sense!
Noel
John Knott
Posted at 21:38h, 12 SeptemberNoel,
Thank you for reviewing our blog and I hope you found it useful. Basically what you are asking is the difference between resistance and impedance. I suggest you read this article which has a good explanation http://www.physlink.com/education/askexperts/ae517.cfm Let me know if you have any other questions after reading this.