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Old June 8th 04, 06:54 PM
Reg Edwards
 
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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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