[ARC5] Why an UNUN?

[J. Forster]

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> On Oct 24, 2012, at 6:45 PM, J. Forster wrote:
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>> Not really.
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> Yes really
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>> A transmitter, like a battery or other power supply, can be modelled
>> as a
>> Thevinin Equivalenrt, an ideal Voltage Source in series with an Output
>> Impedance.
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> The equivalent circuit of a class C amplifier would look like an AC
> (RF) voltage source with a very low internal resistance.
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>> There is a circuit theory theorem that, for maximum real power
>> tranfer,
>> the load impedance should be equal to Complex Conjugate of the source
>> impedance.
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> We're not talking about maximum power transfer here.  A Class C amp is
> designed to provide a particular power output at a high efficiency,
> not maximum power transfer which results in an efficiency of 50% .
> You''re thinking of class A.

The class of the amplifies has nothing to do with the conditions for
maximum power transfer fron the transmitter tank to the antenna.

-John

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> This means equal to, if the source and load are purely resistive.
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>> This means if one is inductive, the other must be capacitive, and the
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> We keep the load resistance seen by the PA tube purely resistive here
> with our resonant tank circuit.   In practice we strive to present the
> amplifier with a purely resistive load if possible. Small values of
> reactance reflected into the tank circuit can be accommodated by
> tuning adjustments.  In those cases where the reactive components are
> too large external antenna 'tuners" are employed.
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>> inductive reactance equals the capacitive reactance.
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>> This means if the source is complex (resistive + inductive), the
>> load must
>> have a load where the resistive componants are equal and the
>> capacitive
>> reactance is equal, and opposite, to the source inductive reactance.
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>> ie:  The L & C are resonant at the operating frequency.
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> See above
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> Dennis D.  W7QHO
> Glendale, CA
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