RF Inductance Meter

Description: This RF inductance meter measures RF chokes in the 500 nH to 50 µH range. A simple solution was required to measure hand-wound RF inductors in a secondary lab setting. The user intended to utilize this device occasionally and did not require advanced features. Plans were made to create a more sophisticated version based on an AT90S1200 design once a friend's project was completed. The existing circuit, which was more complex and included a zero adjustment and range switch, was originally designed for higher inductances. Modifications were made to accommodate available components and to enable operation within the 500 nanohenry to 50 microhenry range. The original circuit was published a few years ago by the American Radio Relay League (ARRL), and this adaptation is shared with appreciation for their work.

The RF inductance meter is designed to accurately measure the inductance of RF chokes, specifically within the range of 500 nH to 50 µH. This application is particularly relevant for hobbyists and engineers working with hand-wound RF inductors, where precision is essential for ensuring optimal circuit performance. The circuit operates by employing a resonant frequency method, where the inductor under test is connected to an oscillator circuit. The frequency of oscillation is influenced by the inductance value, allowing for the calculation of inductance based on the measured frequency.

The circuit includes a simple oscillator, which can be built using a transistor or operational amplifier, and a frequency counter or a microcontroller to measure the oscillation frequency. The design should incorporate a variable capacitor to allow tuning of the oscillation frequency, enabling the user to match the resonance point accurately.

In terms of construction, the circuit can be assembled on a breadboard or a printed circuit board (PCB) for more permanent use. Care should be taken to minimize parasitic capacitance and inductance in the layout, as these can affect measurement accuracy, especially at lower inductance values.

The modifications made to the original design to accommodate lower inductance values involve selecting appropriate component values for the oscillator circuit and ensuring that the measurement range is suitable for the desired applications. The inclusion of a simple calibration procedure is recommended to ensure accurate readings across the entire measurement range.

Overall, this RF inductance meter serves as a practical tool for measuring RF chokes, providing a straightforward and effective solution for those working with low-value inductors in RF applications.This RF inductance meter measures RF chokes in the 500 nH to 50 uH range. I needed a way to measure hand-wound RF inductors in my second lab, and since I would only be doing this occasionally, I didn`t need anything fancy, and since once a friend finishes his AT90S1200-based design, I plan to make one myself, I figured I`d use this for less than a year, so I didn`t want to invest a lot of time in making it . I had run across the forerunner of this circuit, one that is more sophisticated in that it has a zero adjustment and range switch, but it was limited to higher inductances.

I adapted it to the components I had on hand and changed it so that it would work in the 500 nanohenry to 50 microhenry range.The original circuit was reportedly published a few years ago by the Amrican Radio Relay League, so it is with appreciation of the ARRL that I make this circuit available.