"Dave" wrote in message ...
Bob Eldred wrote:

Impedance varies with frequency if there are reactive components, L's and
C's.

That is not always true.

Take
1) A resistor of resistance R in series with a capacitor of capacitance C.

2) Another identical resistor of resistance R, but in series with an
inductor L.

Make R=sqrt(L/C)

and put 1 and 2 in parallel and measure the impedance across that
combination. The impedance is always R, and is independent of frequency.

A useless fact I would admit!!




Not exactly useless, you just described a Zobel network.

It is used as crossover to feed two loudspeaker on HI range and LOW range
presenting a constant resistive load to the Amp.

It is used to compensate a shunt at higher freq. The transfer function is
perfectly flat even with two reactances in the circuit.

It is used to terminate a DC distribution line R+L with a R+C to avoid
resonances, the line is perfectly damped, when the load current steps there
are no oscillatory transients.

MG

MG