> "It all depends ".... on what ? Finish the thought for the benefit of
> the poor guy out there that's trying to learn.
>
> This discussion has completely overlooked the attenuation of harmonics
> as a function of tank Q. You guys need to keep in mind that this
> thread started with a request for advice from someone wanting to build
> their first 4-1000 amp. I haven't seen all that much good advice so
> far; just a bunch of incomplete thoughts and a 4-1000 "expert" that
> has repeatedly "bespoken" himself.
Someone else made a post explaining this one way, but there are
several ways to look at it.
Consider the pi two back-to-back L's. If the center impedance is
not lower than the load and source impedance, the network will not
behave like a pi. That requires a phase shift of more than 90
degrees.
90 degree phase shift occurs when the loading and tuning
capacitors are equal values, and the network electrically looks like
a 1/4 wl long transmission line with a Zo the geometric mean of the
input and output impedances.
You need some value of Q more than just over the square root of
the ratio of the two impedances. So with a 5000 ohm source and
50 ohm load you need a Q of sqrt 100, or ten. When you do that,
phase shift is over 90 degrees lagging and the center impedance in
the pi is less than the lowest end impedance, and the control
behave normally.
Setting Q for harmonics is mostly a waste of time except on paper,
the layout and wiring often has much more effect on harmonics
than the Q of the tank.
If you are really short on harmonic suppression, it is unlikely you
can get enough Q to cure the problem.
73, Tom W8JI
W8JI@contesting.com
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