# Multi Resonant Circuit

#### pionixstar90

Nov 22, 2011
4
I am looking for the RLC circuit which can be resonant at more than one frequency.
In other words, the frequency response of this circuit should show more than one peak (maximum gain).

#### duke37

Jan 9, 2011
5,364
I do not think that this can be done.
A series resonant circuit with a capacitor across it will have a parallel and series resonant frequency but this will give maximumm gain in one case and minimum gain in the other.

Intermediate transformers in superhet radios use two tuned circuits coupled together. The coupling is normally adjusted to give a single peak but if it is increased, a double peak can be attained.

What is the application?

#### KrisBlueNZ

##### Sadly passed away in 2015
Nov 28, 2011
8,393
You should be able to use two L-C circuits together. If you're using parallel tuned circuits, connect the two of them in series, and vice versa.

#### CDRIVE

##### Hauling 10' pipe on a Trek Shift3
May 8, 2012
4,960
I can assure you that supplying us with pertinent information will not hurt.

#### Laplace

Apr 4, 2010
1,252
Here is a MathCAD analysis of one such multi-resonant circuit, including a magnitude plot for a sample set of component values.

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#### CDRIVE

##### Hauling 10' pipe on a Trek Shift3
May 8, 2012
4,960
I do not think that this can be done.
A series resonant circuit with a capacitor across it will have a parallel and series resonant frequency but this will give maximumm gain in one case and minimum gain in the other.

Intermediate transformers in superhet radios use two tuned circuits coupled together. The coupling is normally adjusted to give a single peak but if it is increased, a double peak can be attained.

What is the application?

Actually, the bandpass shape is dependent on the number of poles, coupling coefficient and the Q of each pole. I've worked with such bandpass stages that produced three peaks (F1 - Fc - F2) where F1 and F2 were spec'd @ -3dB min. Fr, Coupling and Q were played with until we got virtually a flat top between F1 & F2 (-3dB bandpass) that made the Pentagon brass happy. These were RF Log Amps that were used in some hush, hush anti radar system.

Chris

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