I have a radio engineering question: What works better in a tank circuit, a coil at its natural frequency that matches the incoming frequency or a coil within range of the incoming frequency?

 

Can you define what you mean by "works better"? The reason I ask is that the resonant frequency of a tank circuit depends on the capacitance of the capacitor in parallel as well as the parasitics. The Q of the tank circuit will depend on the series and parallel resistances. As you may begin to appreciate "works better" is not exactly a measurable quantity by any means.

 

For 'Works better' I mean is there a Q difference?

 

Well, you certainly don’t want to use one with a self resonance below what you want.

 

For 'Works better' I mean is there a Q difference?

For that you basically have to look at the magnitudes of the real and imaginary parts of the impedance. The real part is governed by the DC resistance of the wire and the ESR of the capacitor in parallel.

 

By your reference to "tank circuit" I am guessing that the coil is to be part of a transmitter circuit. The resistance of the coil as well as of the connections, has a big effect on the effective "Q" of a coil in a tuned circuit, especially at resonance. In transmitters and other power circuits with a resonant circuit, a very high "Q" factor will tend toward high currents flowing tn the tuned circuit. THAT can cause problems. The theoretical "Natural resonance" of a coil is from the assorted capacitance between the turns. Normally that is not an issue.

So what are you building?? It sounds interesting.

 

By your reference to "tank circuit" I am guessing that the coil is to be part of a transmitter circuit. The resistance of the coil as well as of the connections, has a big effect on the effective "Q" of a coil in a tuned circuit, especially at resonance. In transmitters and other power circuits with a resonant circuit, a very high "Q" factor will tend toward high currents flowing tn the tuned circuit. THAT can cause problems. The theoretical "Natural resonance" of a coil is from the assorted capacitance between the turns. Normally that is not an issue.

So what are you building?? It sounds interesting.

I am trying to see what range I can put this transmitter into other than its nature one.

 

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I am trying to see what range I can put this transmitter into other than its nature one.

Why?

 

The reonance of your tank circuit is 390Hz.

 

Why?

I am wanting to see the prospect of using a single in ELF.

 

Certainly those capacitor values are way too large for an efficient tuned circuit.

 

I am wanting to see the prospect of using a single in ELF.

Translate that into something usable to mere mortals.

 

Translate that into something usable to mere mortals.

The range of Extremely Low Frequencies.

 

The range of Extremely Low Frequencies.

We know what ELF is but what do you want to do with those Extremely Low Frequencies?

 

Transmitting on those frequencies for any distance requires a lot of power. They were used by the NAVY at one time to communicate with submarines underwater.
In general, resonant circuits tend to greater efficiency when the inductive and capacitive reactances are similar.
NO, I do not have the math to back that claim, it is what I heard from those more familiar with designing resonant circuits than I am.

 

Transmitting on those frequencies for any distance requires a lot of power. They were used by the NAVY at one time to communicate with submarines underwater.
In general, resonant circuits tend to greater efficiency when the inductive and capacitive reactances are similar.
NO, I do not have the math to back that claim, it is what I heard from those more familiar with designing resonant circuits than I am.

https://klubnl.pl/wpr/en/index.php/2022/06/16/analysis-of-zevs-messages/
Russia still uses ELF (82 hertz) for sub communications.

Some have used this for traffic analysis to see if 'events' are planned. The messages are encrypted so you look for unique message signatures of time, periods and other factors instead of content.
https://klubnl.pl/wpr/en/index.php/2022/06/17/zevs-messages-during-the-russian-invasion-in-ukraine/

It’s interesting that the peak of activity is a few weeks before the russian invasion of Ukraine in 2022-02-22:

Today, VLF is the used in the USA sub and sometimes in surface fleet for EAM communications.