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## -SEPTEMBER NEWS LETTERIsotron 10Take advantage of the DX openings.Easy InstallationExcellent PerformanceDurable ConstructionCC&R Friendly (XYL also) You are welcome to contact me at wd0eja@isotronantennas.com with question you may have.RESONANCE IN A PARALLEL CIRCUITThe last article described a Series Resonant circuit. At resonance the voltages across the inductor (L) and capacitor (C) cancelled. This caused the voltage to be minimum and the current maximum. At resonance the series resonant circuit dissipates maximum power. The parallel resonant circuit reacts opposite of the series circuit. When a variable frequency source of constant voltage is applied to a parallel circuit there is a resonance affect similar to the that in a series circuit. However, in this case the applied current is smallest at the frequency for which the inductive (X _{L})and capacitive (X_{C}) reactance are equal (or resonant). At that frequency the current through L is exactly cancelled by the out of phase current through C, so that only a current taken by a resistance (R) flows in the line. R is normally quite high in a parallel circuit.At frequencies below resonance the current through L is larger than that through C, because the reactance of L is smaller and that of C higher at low frequencies. At frequencies above resonance the reverse is true. Where is the parallel resonant circuit used? In our radio equipment it is used where a high resistance is needed at resonance. Such as the input and output of an amplifier stage. To block a specific frequency from affecting a circuit. What about an antenna? Most antennas are series resonant circuits. However, not all are. There are a variety of loop antennas. Some small and some very large. In either case the impedance of the antenna at resonance looks like a pure resistor, but with a maximum value. It can be in the thousands of ohms. This condition does not directly match the 50 ohms of our radios. Therefore, a matching circuit is needed to use it as an antenna. Since the parallel or loop type antennas operate at maximum voltage, losses can be incurred easily. If you are aware of this, the loss may be avoided. Another common area that the parallel resonant circuit is used is in our series resonant antennas. "Traps". Multi-band antennas can use a parallel resonant circuit at a specific distance in the dipole or vertical to block a frequency. Usually the one you want to use. This makes the antenna look shorter for that frequency electrically. The series and parallel resonant circuits give us a variety of ways we can use resonant circuits in our equipment and antennas. 73, Ralph WD0EJA 08-15 If you have questions about the product or articles feel free to contact me. BILAL COMPANY137 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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