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Figure 11-2 Capacitor circuit symbols

Figure 11-3 Various types, shapes and sizes of capacitor

Figure 11-3 shows a variety of capacitor types. Paper capacitors are no longer used.
Electrolytics are generally low voltage and large capacitance. Often used a filter
capacitors in power supplies. Air dielectric (bottom right) are used where the
capacitance needs to be varied and the voltage is high. Trimmer capacitors can be
used to finely adjust the resonant frequency of a tuned circuit or oscillator. Ceramic
capacitors a common in modern transceivers due to their low cost and small size,
used at radio Frequencies. Silver mica capacitors are an inexpensive and can
withstand higher voltages.

Larger 200-400pF air variable capacitors are used in transmitter output stages and
antenna tuners. Air dielectric capacitors can withstand higher voltages. It takes
about 10kV to flash over 1cm of dry air. Notice that besides the capacitance in
farads, capacitors also have a maximum voltage rating.
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