# Creating resonance

Discussion in 'Wireless & RF Design' started by Gunnar H. Laier, Oct 5, 2015.

1. ### Gunnar H. Laier Thread Starter New Member

Mar 23, 2015
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Is there a relatively simple and efficient way of creating resonance within a broad range of the RF spectrum, such that the effect of existing RF fields are enlarged?

2. ### Papabravo Expert

Feb 24, 2006
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Generally speaking the answer is no. In physical terms a circuit exhibits resonant behavior when the inductive reactance is equal to the capacitative reactance.

$X_L= 2 \pi f L$
$X_C = \frac {1}{2 \pi f C$
$f=\frac{1}{2 \pi \sqrt{LC}}$

So the two quantities can only be equal at a given frequency for L and C constrained to a small range. Graphically you can see that the two curves (a line and a hyperbola) intersect at a single point.

Last edited: Oct 5, 2015
3. ### Alec_t AAC Fanatic!

Sep 17, 2013
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Almost by definition, resonance means a sharp peak or trough in response over a narrow frequency range.

4. ### Gunnar H. Laier Thread Starter New Member

Mar 23, 2015
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Theoretical speaking, you have a point when it comes to principles behind electronics.
Notice however the effect on other frequencies in the RF spectrum then emitting distorted RF signals with large near field effect, e.g. RF signals, generated by electronic circuits, consisting of convolutions of sinus wave and 'saw-tooth' waves at higher frequencies (multiple of frequency/wavelength).

5. ### Papabravo Expert

Feb 24, 2006
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Sounds like incoherent rambling, unless I'm missing something.

6. ### Gunnar H. Laier Thread Starter New Member

Mar 23, 2015
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I am saying radio fields aren't electronic circuits.
The phenomenon has been observed across a wide frequency range. Resonance effects observable in multiples of a particular frequency and with different effect proportional to the distance from the center frequency of the emitted field. A consequence of a less precise convolution of two signals.
However, there are more advanced examples, generating more uniform observable phenomena.

7. ### Alec_t AAC Fanatic!

Sep 17, 2013
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Are you talking about ways of generating broadband interference with many harmonics of some basic frequencies? That won't go down well with the authorities or your neighbours or ham radio enthusiasts .

8. ### Gunnar H. Laier Thread Starter New Member

Mar 23, 2015
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I am talking of countermeasures as much as experiments with only near field emissions.
Countermeasures might include setups to detect sources of emission, but also generic solutions to counteract brief attacks on wireless security systems and infrastructure.

The interpretation of the degree of destructiveness depends much on the antenna of an emitter.
No need to turn to mysticism, the enemy possess a knowledge, we should not deny our citizens.

9. ### Kermit2 AAC Fanatic!

Feb 5, 2010
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Is this a question or a diatribe?

10. ### nsaspook AAC Fanatic!

Aug 27, 2009
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What are you talking about? Electromagnetic energy is the same everywhere but you can modify it's local energy distribution by the introduction of a non-linear travel path for that energy for mixing/heterodyne to create new frequencies and/or 'beating' a near frequency for the superposition of signals creating a detectable envelope. Simple harmonic oscillator type resonance effects tend to store energy (Q) that normally would be dissipated in the background as undetectable heat quickly making detection possible above the noise level but all that is common knowledge.

With the correct equipment you can detect a passive resonator (that uses background radio signals as the carrier by modulating changes in the bug devices resonance Q that are then detectable as changes in the RF background noise) easily in a room size space but that's not special knowledge either as they operate like a grid-dip meter that measures the slight changes in energy movement in space as the power drawn from the detection device transmitter changes as it's coupled to the remote passive receiver.

Last edited: Oct 6, 2015
11. ### alfacliff Well-Known Member

Dec 13, 2013
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you sould not use any resonance for that, unless you knew what the frequency of it is. checkout the circuit labled "the fed detector" here. http://www.techlib.com/ for a circuit like that.

Aug 27, 2009
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Mar 23, 2015
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14. ### nsaspook AAC Fanatic!

Aug 27, 2009
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Dude, is your tin-foil hat too tight? Navy weapons systems are harden against nuclear EMP so no little plane can cause real damage. Sure, they could temporally jam the air waves if flying that close but having an IR seeker missile up their tailpipe in a real war far from the ship would make them think better of this childish game.

Last edited: Oct 6, 2015
15. ### Gunnar H. Laier Thread Starter New Member

Mar 23, 2015
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Alice, my tin-foil hat is not even on. I left it in the Faraday cage.

I just wanted you to straighten your imagination, since the topic moved to topics on bugs and not interference. Admittedly I do not bring much invention to this forum, but your directives was interesting.

So, what do you recommend for venturing into these shallow waters ... ?

16. ### Gunnar H. Laier Thread Starter New Member

Mar 23, 2015
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"Suddenly starting or stopping a sinusoidal signal generates a wide spectrum. Even though the frequency of that sinusoid is far removed from the resonance of the LC circuit, some of the sideband energy caused by a high dv/dt will cause the LC tuned circuit to ring a little bit, especially if it has a high Q. (Hams call this key clicks).

The circuit would be excited by any high dv/dt signal, regardless if it is a sharply keyed sinusoidal signal or something else"

17. ### nsaspook AAC Fanatic!

Aug 27, 2009
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Yes, electrically it's like ringing a bell with a quick rap from a solid rod or the drop of a piano hammer on the tight string of the sounding board. Instead of mechanical motion and moving mass you have the electrical energy entering the circuit being stored and released in time back and forth as electric and magnetic fields in the reactive components and/or parasitic impedance of the components.

If you visualize the spinning wheel as the LC circuit with the RF energy as the circular motion of its rotation you can see how RF waves are made.

Last edited: Oct 6, 2015
18. ### Gunnar H. Laier Thread Starter New Member

Mar 23, 2015
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Ok, and besides the poetry. Signal generators, RLC circuits, amplifiers and antennas - what is the point of building those in vain or of low quality, when others have already done so. Where are the adjustable, flexible designs, schema and simple affordable components lists and the textbook to rule them all.
Recommendations (English, German or Russian titles)

19. ### nsaspook AAC Fanatic!

Aug 27, 2009
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Read and understand this book to find out.
http://www.mhhe.com/engineering/electrical/hayt/

Last edited: Oct 6, 2015
20. ### Gunnar H. Laier Thread Starter New Member

Mar 23, 2015
13
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Thanks nsaspook! It seems to be a nice textbook.
Do you have recommendations for a lab book?