I have a project that requires applying audio frequency noise to an emitter coil. The signal strength is about 4 watts.
Are there any regulations in the US restricting broadcasts in this frequency band?
Robert Martin
There are plenty of loudspeakers doing almost the same thing at higher powers although they are trying to move the speaker cone to pump air.
How much of that input power do you really expect to actually broadcast and how much of it will simply be dissipated as resistive heating?
It will obviously interfere with any nearby deaf aids on their T setting for inductive loops. There may be some restrictions on some spot frequencies used for ULF communications with submarines but I expect they will come and kick your door down if you start jamming them.
-- Regards, Martin Brown
If over 9 kHz, I believe the answer is "yes". That's from memory, and I have not had my morning cup of coffee yet. You'll need to check FCC Rules Part-15 (Unlicensed, low power operation).
You won't make enough field for anyone to notice.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
RIGHT! I mean, look at the power utilities! They've got hundreds of amps flowing through wires hundreds of miles long. Technically, anything over 9 KHz can be a problem, but the fields you cause with a 4 W drive is very unlikely to be detectable outside a building.
Jon
OK. Sounds good. I will look out for hearing impaired people on submarines.I expect there will soon be a law protecting them that will put us all out of business.
Robert Martin
ITU (International Telecommunication Union) Radio Regulations defines frequency allocations for frequencies above 9 kHz and most national rules are based on ITU RR, so frequencies below 9 kHz should be free for all i most countries.
The EU RED directive goes below 9kHz, which is targeted directly on radio equipment:
"This is also the first time that equipment operating below 9 kHz requires radio testing as the RED scope is for products operating below 3000 GHz, whereas the R&TTE scope started at 9 kHz."
It might be useful to see what natural phenomenon and radio services you might be interfering with. Not that these are all ITU bands:
ELF 3 to 30 Hz. Schumann resonances and submarine communications.
SLF 30 to 300 Hz. More submarine communications.
ULF 300 - 3000 Hz. Magnetosphere science and seismology.
VLF 3KHz to 30KHz. Radio Navigation, time signals, submarine communications.
LF 30KHz to 300KHz. Longwave broadcast, time signals, and old Loran navigation system.
However, don't worry. 4 watts of RF into any sort of small coil antenna is not going to be seriously inefficient and therefore not have much range. If you're at a university, check if anyone is doing atmospheric research as you're likely to create some local interference.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
Jabbut look out for harmonics. Any distortion will flip part of the power into the forbidden zone.......
This page might help: "Radio Waves Below 22KHz"
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
** Hearing aid loops use far more power to cover large areas, like whole rooms or auditoriums.
Don't bother one of them and your " emitter coil " whatever that is never likely to be noticed.
.... Phil
** Long distance distribution cables operate in 3 conductor / 3 phase and are carefully balanced. Even fairly close to the cables, there is very little residual electric or magnetic field.
Even the conductors installed in your house travel in pairs, carrying equal currents in opposite directions so cancelling external fields.
.... Phil
Yes, the house conductors are closely paired, and don't generate much field. But, the high tension lines are a hundred feet (or more) above the ground, and while the currents are balanced, the height of the wires varies in some systems, and the outer phase wires are quite far apart in others. The fact that radiation losses are significant and ground heating is a measurable loss tells me that the fields are not so little. Look on Youtube for pictures of guys holding fluorescent tubes under power lines to see the magnitude of the electric field. And, check out how people who tap power off metal fences get prosecuted for stealing power, that shows that the magnetic fields are pretty strong, too.
Jon
True for cables and at least for the fundamental frequency, not so sure about harmonics.
For more than a decade many companies tried to use PLC (Power Line Communication) over mains low voltage distribution wires for Internet connectivity. Typically frequencies up to a few MHz were used. Unfortunately it radiates like hell from light switch wiring with no neutral to the light switch. These wire stubs are typically a few meters long, so conveniently a 1/4 wavelength on some of the PLC frequencies, being very effective radiators :-(. For this reason, there were a lot of opposition from legitimate radio services.
Do they get prosecuted for the warming of their rose gardens and swimming pools?
I figure that if someone dumps a magnetic field onto my property, it's mine.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
Trust the EU to make life difficult.
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The real issue is the stray capacitance between the phase conductor and ground on long lines. For this reason, the position of a specific phase conductor is varied in different poles, so there is about an equal stray capacitance from each phase conductor to ground.
For long lines, a significant amount of current is needed to charge and discharge this stray capacitance. Ultimately no current carrying capacity is available to carry any real power [W], when the full apparent power [VA] goes into reactive power [VAr]. You need to insert compensation stations at regular intervals to compensate for the capacitive reactive power so that real power can be transported.
While it would be possible to touch one conductor of a ground isolated delta feed and the two phase conductors would just be at higher potential, touching one phase conductor will kill you due to the energy stored in these stray capacitances.
The capacitance issue is much worse for underground and undersea cables, one is forced to use HVDC feeds on long submarine cables.
To get some glow out of such tubes only requires a milliamp or two.
snipped-for-privacy@downunder.com wrote in news:f2j00e97gon41dblggg0c2jkt711g74r0s@
4ax.com:
Not if you are wearing a (full body) mesh suit.
John Larkin wrote in news: snipped-for-privacy@4ax.com:
I made a VLF design a couple years ago.
The antenna was 18 inches long, an inch thick and an inch and a half wide (just the core). Each one weighed like 6 lbs. We also incorporated a nice Delrin box for it. It was 50 strips of mu metal I hand cut from a coil of it. And the wire was 14Ga. and we fired it with 1500 W.
We were able to recv over a mile away.
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