Vacuum Condenser Applications and Benefits

Inside a vacuum capacitor, two metal (usually copper) electrodes are separated by a vacuum. The outer part of the capacitor is made of glass or ceramic. They typically have low capacitance in the 10 to 1000 pF range and high voltages, typically 5000 volts and above. Vacuum capacitors find wide application in industrial radio frequency power applications. They are used in equipment such as high power broadcast transmitters, radio frequency amplifiers for radio amateurs, and large antenna tuners. Vacuum capacitors can also be used as part of the impedance variation in automatic matching. Variations of vacuum capacitors include fixed and variable. The main difference between fixed and variable is that variable vacuum capacitors can be adjusted.

Vacuum variable capacitors must be able to handle high voltages. A typical high power amateur radio or AM broadcast transmitter will have a DC potential of 1500 to 7500 V at the anode of the RF amplifier, depending on the type of tube. In the case of AM, this potential can be doubled. Certain faults within the system can also increase RF voltages, so a variable capacitor used in the final amplifier’s anode circuit must be able to withstand these potentials.

The vacuum is the most perfect of dielectrics with a zero loss tangent. What this means is that very high powers can be transferred without significant loss and heating; units repair themselves after moderate overloads. Compared to other variable capacitors, vacuum variables, due to the vacuum itself, are more accurate and stable. The sealed chamber means that the dielectric constant remains the same over a wider range of operating conditions. By using vacuum variable capacitors, designers have been able to produce smaller transmitters that offer better and more reliable performance, and are easier to tune and keep in tune.

For high power transmitters and other high voltage capacitor applications, vacuum capacitors are used for power amplifier tank circuits, output pi networks, neutralization circuits, plate and grid blocking circuits, antenna coupling, and circuits. bypass “rejection”, pulse shaping in the output circuit. magnetrons, bypass capacitors for harmonic attenuation, dielectric heating equipment tank circuits, high-current, low-inductance shunt applications, and non-magnetic capacitors for resonance imaging. Vacuum capacitors are used in longwave, mediumwave (MW or AM), shortwave, and VHF (FM and TV) broadcast transmitters. They also serve in broadcast antenna systems, particularly AM directional antenna phaser systems, diplexers, triplexers, and line tuners.