Any wire that carries AC current creates RF. Shielded cable might shield it, but all conductors with an electric current that changes emit EM radiation.
Only the amount is insignificant since: 1 - the length of the circuit is insignificant compared to the wavelength 2 - there are 2 conductors carrying current in opposing directions effectively canceling the field.
For all practical purposes the field generated is 0.
Any wire that carries AC current creates RF. Shielded cable might shield it, but all conductors with an electric current that changes emit EM radiation.
Only the amount is insignificant since: 1 - the length of the circuit is insignificant compared to the wavelength 2 - there are 2 conductors carrying current in opposing directions effectively canceling the field.
For all practical purposes the field generated is 0.
Take the input to any audio amplifier, and attach a small piece of wire or even your finger and touch it.
The 'hummmmmmm' you hear is radiation from the AC powerline.
Take the input to any audio amplifier, and attach a small piece of wire or even your finger and touch it.
The 'hummmmmmm' you hear is radiation from the AC powerline.
It's capacitive coupling. Not to be confused with electromagnetic radiation. If you unplug all loads from a house the measured active power is pretty much the amount of power radiated. Zero. If any significant amount of energy would be radiated then a GFI would trip instantly.
[2 - there are 2 conductors carrying current in opposing directions effectively canceling the field.
I don't think it works like that.
You might not think it does, but the reality of it is, cowboyro is quite correct.
The primary factor required in order to generate a decent amount of a radiated signal, canceling excluded, is one needs a radiator tuned to the to the frequency to be radiated, which for a 60Hz quarter wave antenna is roughly 4 million feet, and unless you are dealing with a rather large structure I am willing to bet that is probably not going to be found in a straight run.
It's capacitive coupling. Not to be confused with electromagnetic radiation.
Wait, what?
It's the same thing.
Nope. Capacitive coupling and RF pickup are 2 very different things. Capaqcitive coupling works only over relatively short distances while RF pickup, as long you have a powerful enough transmitter and a sensitive enough receiver, can work over very-very long distances.
It's capacitive coupling. Not to be confused with electromagnetic radiation.
Wait, what? It's the same thing.
Nope. Capacitive coupling and RF pickup are 2 very different things.
The actions of any capacitor work because of an electromagnetic field. Nothing more, nothing less. Radio waves are also due to electromagnetic fields. See: Electromagnetic fields, Maxwell's equations. The only difference between the two is that at a capacitor the near-field equations apply & the 'electric' portion of the field is stronger. It is still an EMF based on moving electric charges and does indeed radiate. Unless its part of resonant circuit, its not very useful as a transmitter.
quote:In the past, electrically charged objects were thought to produce two different, unrelated types of field associated with their charge property. An electric field is produced when the charge is stationary with respect to an observer measuring the properties of the charge, and a magnetic field (as well as an electric field) is produced when the charge moves (creating an electric current) with respect to this observer. Over time, it was realized that the electric and magnetic fields are better thought of as two parts of a greater whole — the electromagnetic field.
if either the electric or magnetic field has a time-dependence, then both fields must be considered together as a coupled electromagnetic field using Maxwell's equations. A changing electromagnetic field which is physically close to currents and charges (see near and far field for a definition of “close”) will have a dipole characteristic that is dominated by either a changing electric dipole, or a changing magnetic dipole. This type of dipole field near sources is called an electromagnetic near-field.
It is still an EMF based on moving electric charges and does indeed radiate. Unless its part of resonant circuit, its not very useful as a transmitter.
Which in turn means that the amount of energy radiated is negligible.
It is still an EMF based on moving electric charges and does indeed radiate. Unless its part of resonant circuit, its not very useful as a transmitter.
Which in turn means that the amount of energy radiated is negligible.
Doesn't mean anything. He's just shunting the air gap between the lines and the ground creating a path for the current to flow. You can make a fluorescent tube glow from the static charge you collect.
Doesn't mean anything. He's just shunting the air gap between the lines and the ground creating a path for the current to flow. You can make a fluorescent tube glow from the static charge you collect.
Actually most of what is radiated from powerlines is through electromagnetic induction or EM which is how this works. There is still some ELF being radiated but it is pretty small. It is still there though, and it's how touch lamps and other touch controls used to work (I have no idea if they still use that).
Actually most of what is radiated from powerlines is through electromagnetic induction or EM which is how this works. There is still some ELF being radiated but it is pretty small. It is still there though, and it's how touch lamps and other touch controls used to work (I have no idea if they still use that).
Those are capacitive sensors. The vectors of the electric and magnetic field are perpendicular to the direction of propagation. EM radiation would induce a current in a receiving "antenna" placed parallel to the wire.
Actually most of what is radiated from powerlines is through electromagnetic induction or EM which is how this works. There is still some ELF being radiated but it is pretty small. It is still there though, and it's how touch lamps and other touch controls used to work (I have no idea if they still use that).
Those are capacitive sensors. The vectors of the electric and magnetic field are perpendicular to the direction of propagation. EM radiation would induce a current in a receiving "antenna" placed parallel to the wire.
I think that's what my Samsung LNT5271F has (silver strip below the SAMSUNG logo)
The vectors of the electric and magnetic field are perpendicular to the direction of propagation. EM radiation would induce a current in a receiving "antenna" placed parallel to the wire.
Even if it weren't parallel there would still be some induction.
Even if it weren't parallel there would still be some induction.
Not if the "antenna" is perpendicular. Those tubes would glow even if the lines were carrying DC. DC does not generate EM radiation. Example of fluorescent glow with a Van de Graaff generator:
