Variable Capacitors

Most of our air-dielectric variable capacitors work on the principle of two oppositely-charged intermeshing banks of plates; capacitance varies when the shaft is rotated, varying the degree to which the two banks "shade" one another. Applications of our capacitors are myriad: They include everything from plasma etching and deposition equipment to crystal radios. All of these applications share a few common traits, however: They require a capacitor capable of virtually instantaneous tuning, with high Q and low loss at high frequencies.

The family of configurations represented by the M73, M90, and M97 consists of large, high-quality units, overbuilt in terms of physical and electrical durability. They are used in applications that require a high maximum voltage, large capacitance, and durability. A typical application is in RF matching networks; M73s are generally used in pi networks, while M90s and m97s can often be used to replace vacuum variables in L networks.  Each of these configurations lends itself well to customization and can be economically produced in small or large quantities.

>The APL, APC, and ATM are small capacitors built around a ceramic insulator. They are much smaller and more economical than the M73, especially in large quantities, and are used in RF tuning equipment where loss and Q are critical.

The N50, S2, and S3 are built into a C-shaped frame with ball bearings, and are used in applications that require an economical price in large quantities, high capacitance in confined spaces, and special relationships between rotation and capacitance.

OEP also manufactures custom capacitors; we can design a capacitor to meet a specific set of performance criteria, or we can manufacture a capacitor to a customer's design spec. Custom capacitors that we've manufactured include (but aren't limited to) fixed air-dielectric capacitors, screw-type trimmer caps with air and Teflon dielectrics, and several modifications of our own capacitors with special mounting features, drive units, hybrid designs incorporating other elements of the customer's design (like pc boards or inductors) into the structure of the capacitor itself, or modifications that replace the air dielectric in a variable cap with Teflonę, paralene, pressurized gas, or oil.

The graph and chart below can serve as a guide to which of our configurations can meet your needs. Voltage is graphed along the horizontal axis and capacitance along the vertical; to determine which configuration would be best suited to an application requiring a particular maximum voltage and maximum capacitance, plot the point determined by these two coordinates, and determine the region in which it lies. If, for example, you need a 400 pF capacitor that can withstand 1500 Vrms, plot the point (1500,400); it lies in the pink colored zone, so an M73 would work.


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