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MARCH NEWS LETTERISOTRON 600 NETHERLANDS FOR THE AM BROADCAST BAND THE BEST WAY TO OPERATE HF & MW EASY INSTALLATION EXCELLENT PERFORMANCE DURABLE CONSTRUCTION CC&R FRIENDLY (XYL ALSO) I have been publishing this technical article since January of 2013. For the past 44 years I have manufactured the Isotron Antennas. This also involved helping many with their very difficult installations. Some of the information will be from what we learned solve these problems. Some information will be right from a text book or credible article. WHAT IS IN A CAPACITOR? - PART 2 The last issue described some basics of a capacitor. This issue will continue on this subject. How do we measure the size of a capacitor? The fundamental unit of capacitance is the farad, but this unit is much too large for practical work. Capacitance is usually measured in "microfarads" (uf) or picofarads (pf). The microfarad is one-millionth of a farad, and the picofarad is one-millionth of a microfarad. Capacitors nearly always have more than 2 plates, the alternate plates being connected together to form two sets. This makes it possible to attain a fairly large capacitance in a small space, since several plates of smaller individual area can be stacked to form the equivalent of a single large plate of the same total area. Also, all plates, except the two on the ends, are exposed to plates of the other group on both sides, and so are twice as affective in increasing capacitance. What type of capacitors are used in our radios? The types of capacitors used in radio work differ considerably in physical size, construction and capacitance. In variable capacitors (almost always constructed with air for the dielectric) one set of plates is made movable with respect to the other set so that the capacitance can be varied. Fixed capacitors, that is, assemblies having a single, non-adjustable value of capacitance, also can be made with metal plates and with air as a dielectric, but usually are constructed from plates of metal foil with a thin solid or liquid dielectric sandwiched in between, so that a relatively large capacitance can be secured in a small unit. The solid dielectric commonly used are mica, paper, certain plastics and special ceramics. The "electrolytic" capacitor uses aluminum foil plates with a semi-liquid conducting chemical compound between them; the actual dielectric is a very thin film of insulating material that forms on one set of plates through electrochemical action when a DC voltage is applied to the capacitor. The capacitance obtained with a given plate area in an electrolytic capacitor is very large, compared with capacitors that have other dielectrics, because the film is so thin, much less than any thickness that is practicable with a solid dielectric. A word of caution about electrolytics, be sure to watch the polarity. The capacitors are always marked negative and positive. Reversing polarity can be quite exciting. However, some would feel more at home if there was a bit of an explosion associated with their project. The use of electrolytic capacitors is mainly used in power supply filtering and audio bypass applications. Other types of capacitors are used throughout the frequency range from audio to the high RF spectrum. 73, Ralph WD0EJA 10-16 BILAL COMPANY 137 MANCHESTER DR. FLORISSANT, CO. 80816 U.S.A PH/FX: 719/687-0650 OUR EMAIL LIST IS ACQUIRED BY PERSONS WHO HAVE CONTACTED US IN THE PAST. IF YOU DESIRE NOT TO BE CONTACTED PLEASE EMAIL YOUR REQUEST. |
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