[Amps] Tuned Input

[Roger D Johnson]

Tony King - W4ZT wrote:
> I don't know if any of you have looked into this particular product but 
> at first glance it appears that this is one solution for the tuned input 
> problem many of us face and at the right price too:
> 
> <http://www.ldgelectronics.com/manuals/AT-100AMP%20Manual.pdf>
> 
> 73, Tony W4ZT

The purpose of the tuned input is to provide a "flywheel" effect to
smooth out the variations of amplifier input impedance over the
operating cycle. The Q of the circuit determines how much "flywheel"
effect we have. The lowest recommended value I've seen is 2. Solid
state transceivers want even more...perhaps 3 to 5.

The LDG tuner is an L network in which the Q is dependent on the ratio
of impedances to be matched. For normal input impedances, the resulting
Q will be very low. It's hard to write the formula in text format but
in words it's as follows: divide the higher impedance by the lower,
subtract 1 and then take the square root. For example to match an
impedance of 100 ohms to 50 ohms, the resulting Q is only 1!

With a 3 terminal network you can choose the Q independently of the
matching and would seem to be the way to go.

73, Roger


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