Within a vacuum capacitor, two material (copper usually) electrodes are separated by a cleaner. The exterior part of the capacitor is made from either glass or ceramic. They generally have a low capacitance in the range of 10 to 1000 pF and high voltages, typically 5000 v and higher. Vacuum capacitors find wide application in professional applications of r / c frequency energy. They are being used in equipment such as powerful broadcast transmitters, Novice radio RF Amplifiers and large antenna tuners. Pressure capacitors can even be used as the impedance variation part in computerized matching. Different versions of vacuum capacitors include fixed and variable. The main difference between preset and variable is the fact variable vacuum capacitors could be adjusted. rf capacitors
Vacuum varying capacitors need to be able to handle high voltages. A typical high power ham radio or AM broadcast transmitter will have a dc probable of 1500 to 7500 V on the RF amplifier anode, dependent on the sort of tube. In the case of AM, this potential can double. Particular defects within the system may also increase RF voltages, so a varying capacitor used in the ultimate amplifier anode circuit must be capable of stand these potentials.
Vacuum is the most perfect of dielectrics with an actually zero loss tangent. What this means is that quite high powers can be moved without significant loss and heating; the units are self-healing after moderate overloads. Compared to other changing capacitors, vacuum variables, due to vacuum itself, are more precise and stable. The sealed chamber means the dielectric frequent remains the same on the wider range of operating conditions. Through the use of cleaner variable capacitors, designers have been able to create smaller transmitters offering better, more reliable performance, and are much easier to tune and keep in touch.
For high power transmitters and other high voltage capacitor applications, vacuum capacitors are being used for power amplifier tank brake lines, output of pi sites, neutralizing circuits, grid and plate blocking circuits, antenna coupling and “rejecter” faucet circuits, pulse shaping in the output circuit of magnetrons, feed-through capacitors for harmonic attenuation, dielectric heating system equipment tank circuits, low-inductance, high-current bypass applications, and non-magnetic capacitors for reverberation imaging. Vacuum capacitors are utilized in broadcast transmitters for long wave, medium influx (MW or AM), brief wave, and VHF (FM and TV). They also serve in broadcast antenna systems, particularly in WAS directional antenna phasing systems, diplexers, triplexers and range tuning units.