According to information from Nikola Tesla's patent US1119732A, the EXTRA coil serves the Wardenclyffe tower, which is related to the wireless power transmission legend.
Apparatus for transmitting electrical energy
Tesla's EXTRA coil is a coil consisting of 2 ends, one end is connected to a longitudinal waveform electromagnetic resonance circuit, and the other end is connected to two overhead metal hemispheres.
Extra coil on Apparatus for transmitting electrical energy:
Figure 1: The system to promote the longitudinal solenoid behind the resonance process. Extra coil is connected in series with the oscillator circuit
Circuit for position of Extra coil:
Figure 2: The Extra Coil is featured on the Colorado Springs Notes
Thus, the Extra coil is only a small part of a longitudinal electromagnetic wave resonant electronic circuit. According to the circuit diagram, this coil works when connected in series with the famous Tesla Coil, and it was used to develop radio technology. Note: "longitudinal electromagnetic wave" is exactly called Longitudinal Magneto-Dielectric, denoted by LMD. Strictly speaking, it is the longitudinal disturbance of the dielectric in the Ether.
The question is: how does the electronic circuit resonate? What does it mean ?
The meaning is said in one brief sentence: Create Ether tension on another level.
The secret behind the Extra coil: longitudinal electromagnetic wave resonant circuit
Master Ivo is Tesla's Radiant Energy expert, he has studied many documents and found that the Extra coil is connected to the resonant circuit. And even in patent US37181707A it says the same.
Nikola Tesla's EXTRA Coil by Master Ivo:
Master Ivo: Nikola Tesla's Extra coil, was used in his Colorado Springs experiments, and in his Wardenclyffe Tower. But what purpose dit it serve? I series connected an extra coil to my secondary, and measured voltage an current, which opened my eyes wide.
Extra coil and resonator circuit diagram:
This is an improved Radiant Energy circuit in 2020, especially with an Extra coil.
See the circuit in 2020:
Resonant circuit with 3 Bifilar coils, generating radiant energy - Free energy
If you don't know about Bifilar coil, and why it can generate longitudinal electromagnetic waves, then check out this article: Bifilar Coil
As you can see, if Tesla's Extra coil is omitted, the free energy is still present, meaning the output power is greater than the input power (Overunity). So what is the Extra coil for? Or, an equivalent question: What does Tesla's Wardenclyffe Tower use the Extra coil for?
The answer is for readers!
Master Ivo himself did not want to answer that question. Because he wants to leave it to the readers to find out for themselves.
Developing today's Extra coil And the problem of developing Ether field physics technology
Eric Dollard is an expert on Ether technology. He was trained by the American corporation RCA to develop radio technology. Which means what he learned was real Tesla technology, not fake. In a book by Eric Dollard it is said that the Extra coil is connected to the secondary coil of the Tesla Coil, for the purpose of broadcasting radio waves, In fact, to generate longitudinal electromagnetic waves.
Therefore, today's telecommunications technology still uses Extra coils to transmit information. Can Extra coils and circuits in today's radio and telecommunications technology have improved circuitry. But in essence, it must have the Extra reel.
Today's mobile phones also use Extra coils to broadcast to the switchboard, then the total decompresses the frequency and broadcasts to other phones for communication. A phone with a small battery, with a capacity of a few watts, can broadcast to a switchboard a few tens of kilometers away, hundreds of kilometers away. If it weren't for longitudinal electromagnetic waves, it wouldn't be able to travel that far. The transverse electromagnetic waves described by Maxwell's equations cannot travel that far, even compressed at high frequencies.
Evolution of today's Ether field physical technology:
Tesla Radiant Energy is essentially a technology based on the understanding of Ether. Today, scholars, students, they are taught that Ether does not exist. It's just a belief that comes from word of mouth from official documents. If studied closely, mainstream science itself does not dare to completely disprove Ether.
At the moment there are Eric Dollard, Ken Wheeler, Master Ivo,... and some other experts who are developing and researching Ether field theory. Ken Wheeler and Master Ivo are more liberal than Eric Dollard. Because Eric Dollard at the present time doesn't talk much about the truth anymore, he is still developing high frequency radiant energy. Earlier, Eric Dollard revealed quite a lot about alternating current (AC) generators, which are actually free energy generator. Maybe he's banned from developing and disclosing free energy AC generators.
Kenneth Wheeler: “The day science begins to study non-physical phenomena, it will make more progress in one century than in all the previous centuries of its existence.” — Nikola Tesla. Let us simplify this in saying "Science will advance father and faster when Fields & Metaphysics are comprehended and studied". All 'things' (phenomena) are from, by, and due to FIELDS, which are non-physical phenomena. No branch of science has or can define the term FIELD (Khora), nor the term energy for that matter. The most wise minds who ever lived, Pythagoras, Plato, Plotinus, etc. were metaphysicians. The study of metaphysics is the quest to grasp the substrate, or foundation for all else that comes after and from the same. Genuine metaphysics is both hyper-rational, logical, & is a lost field of study which is most important. Only an upside-down world would choose not to study that which is MOST important.
Problem of developing Ether field physics technology
Finally, If you want to make a free energy generator - radiant energy; or start with an experiment to study Ether and Electricity, or in the future develop Ether technology with flying saucers - anti-gravity, you can start with these electronic components:
List of necessary electronic components for Radiant Energy generator