Understand the Functionality of Variable Capacitors

What You Need to Know About Variable Capacitors

If you have noticed a large variable capacitor, you may have observed that some of its plates have slots cut into them. Why is this the case? The answer is simple: you can bend the tabs formed by these slots to increase or decrease the capacitance in small amounts for tuning purposes. For instance, if you have a radio receiver with a dial, you can adjust the capacitor so that certain positions on the dial correspond to exact frequencies. It’s evident that adjustments can only be made within bands, depending on the number of slots that the capacitor features. Sometimes, adjustments do not set the oscillator's frequency. For example, the Delco radio discussed uses the capacitor to maximize tuning at a specified frequency. Typically, the slots are found only on the plates at the ends, and as you can see in the video, not all capacitors possess these slots. Of course, bending the plates, whether they have slots or not, will cause changes. However, it is advisable to avoid bending too much to prevent contacting an adjacent plate or fixed plates when the capacitor is engaged. Not all variable capacitors share the same design; numerous unusual configurations have been encountered.