[AMPS] parasitic suppressors

[Peter Chadwick]

Something I don't understand - maybe Carl or Rich or Jon can explain.

If I take an inductor (start with a 'perfect' inductor) and put a resistor
in series with it, at LF it looks like the inductor isn't there. If I make
the inductor out of resistance wire, it still looks like a resistor. 

Now increase the frequency. Inductive reactance rises, and the Q, given by
2*pi*F*L /R increases, eventually becoming infinite at infinite frequency
(OK, 
3-500s don't have any gain there!) So I have a series inductive reactance
with Q increasing with frequency.

Now take the coil, wind it out of silver tape if you like, and put a 33 ohm
resistor across it. At this stage, it's a perfect resistor. At LF, the low
reactance of the coil shorts out the resistor, but as the frequency rises,
so does the coil reactance. Because it's a parallel circuit, the impedance
tends asymptotically to 33 + j0. Even a practical resistor will tend that
way. As Q is Rp/1*pi*F*L, the Q is falling with frequency - in fact, it will
have a maximum value at VLF.

If I understand Rich's argument, the Q of a paraistic suppressor should fall
with increasing frequency. So there seems to me to be an anomaly - from the
above argument, an L-R shyunt circuit is indicated.

can someone explain?

73

Peter G3RZP

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