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![]() "Bill Hennessy" wrote Is their a set rule on how meny turns of the antenna coil is to the tuneing coil? And would it depend on if you wind it over or next to the tuneing coil? ================================= There are no rules except normal network analysis rules. The generator is the antenna with its internal impedance Ra - jXa. Generator volts is field strength times effective height of antenna. The primary coil has optimum inductance when it resonates with -Xa. The secondary coil inductance resonates with its parallel tuning capacitor at the same frequency. The coefficient of coupling beween the two coils is set to its optimum value of - K = 1 / Sqrt( Q1 * Q2 ) or somewhat greater. where Q1 is the primary circuit Q taking antenna resistance Ra into account, and Q2 is the Q of the secondary circuit coil. So everything depends on frequency, antenna length, ground loss resistance, coil Q, coupling coefficient, and value of tuning capacitor. The calculations are quite simple. For the medium waves and a 40 feet antenna, the primary coil has a wave-winding of many turns spaced a little apart from the secondary coil. The coupling is fairly loose, K about 0.1 The secondary coil is wound on the same former and is usually a single-layer, high Q solenoid. But everything is very non-critical and almost anything will work. Over the wide medium wave band it is impossible to keep anything near optimum. Just find some wire and start winding. ---- Reg, G4FGQ |
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