Showing the two resonance frequencies.

wrote in message
...
Showing the two resonance frequencies.


I picked these two formula from;
http://www.rfcafe.com/references/ele...rmulas-rlc.htm

This one is labeled;

Impedance Z



This one is labeled;

Magnitude [Z]



I don't understand the difference, although the top one has an imaginary
part to it.
I don't know how you can get the answer without j but it does go away at
resonance.
Can you explain the two, Impedance Z vs. Magnitude [Z] to me.
Is this just the two resonant frequencies?

Also which one applies to a tuned crystal radio.

Thanks, MikeK

On Fri, 22 Oct 2010 07:08:19 -0700, Fred Abse
wrote:

On Sun, 17 Oct 2010 10:10:26 -0500
"amdx" wrote:

wrote in message
...
Showing the two resonance frequencies.


I picked these two formula from;
http://www.rfcafe.com/references/ele...rmulas-rlc.htm

This one is labeled;

Impedance Z



This one is labeled;

Magnitude [Z]



I don't understand the difference, although the top one has an imaginary part to it.
I don't know how you can get the answer without j but it does go away at resonance.
Can you explain the two, Impedance Z vs. Magnitude [Z] to me.

I threw together the attached pdf that might help.


Is this just the two resonant frequencies?

No it isn't, the two resonant frequencies a

1. The frequency at which the impedance of the parallel tuned circuit is
maximum magnitude.

2. The frequency at which the current into the parallel tuned circuit is
in phase with the voltage across it, ie. the impedance is purely
resistive.


Also which one applies to a tuned crystal radio.

Probably the first, since you are wanting to tune for maximum voltage.
Unfortunately, this is the more complicated case to calculate. If the Q is reasonably high (50 or above), the difference between the two is
negligible.

With the capacitors generally used in tuned RF circuits (polystyrene,
silver-mica, if you can still get it), capacitor losses may be neglected, and you can assume that all the resistive losses are in the inductor, which simplifies things a lot.

I use "p" for normalized frequency: "s/omega-naught"

...Jim Thompson
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