On Nov 20, 4:36 pm, "Joel Kolstad"
wrote:
Hi Roy,

"Roy Lewallen" wrote in ...

Sorry, no. EH antenna inventors and apologists notwithstanding, the phase of
current doesn't change as it goes through a capacitor.Agreed. I'm being rather loose in my terminology here, what I mean by "you
get 90 degrees of phase shift going through the capacitor" is that the voltage
across the capacitor ends up (must be) 90 degrees out of phase with respect to
the reference current as you consider the capacitor's effect.

You don't disagree that the voltage at the top of a tapped capacitor L-C tank
is 180 degrees out of phase what that at the bottom at resonance, do you?

---Joel

Joel, what do you mean by "at the top" and "at the bottom"? Voltage
measured with respect to what point? Clearly, if there is the same
current through two capacitors in series, the voltages across each of
them must be in phase, so the total voltage across the two is the
simple arithmetic sum of the voltage across each. That assumes that
they are ideal capacitors, but practical ones will come close. On the
other hand, the currents in the two may not be exactly in phase, as you
perhaps discovered with your low-Q tank. If the current at the node
between the capacitors is contributed to by some external load or
source, and if that additional current is not small compared with the
tank's circulating current, then the capacitor currents may not be in
phase, and the voltages then would also not be in phase, and you'd need
to add them vectorially to get the right result.

Of course, Spice will simulate all this for you very nicely, using
either a transient analysis, or a frequency-domain analysis if all the
parts can be assumed to behave linearly.

Cheers,
Tom