I cannot seem to find any information on this subject for the United States. Are there any public bands one might be able to use for an AM transmitter? Is it legal to transmit over an unused AM radio channel if your transmitter has a really small output power? My idea is to attempt a wireless intercom circuit in my own house, but I don't want the FCC knocking at my door or to get into any legal trouble if I can succesfully accomplish this. My circuit will just operate on a 9V battery or less.

 

I think you need a licence after 200ft? I am not sure. Someone else know the exact distance?

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The keywords to use are "low power broadcast" when searching. Here is a good site with info:

http://www.fcc.gov/mb/audio/lowpwr.html

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RadioRon

 

I believe for the AM broadcast band (540 to 1700 kHz), output is limited to 1/10th watt and antenna length is limited to 3 meters to be legal without a license.

How will your intercom work? Just one transmitter and an AM radio to receive?
Could be a fun project, but keep in mind anyone in the area will be able to eves drop on you. Be carful what you use it for.

Commercial made wireless intercoms operate on a much higher freq.

 

If you filled in your location we might be able to provide you with more help.

In the UK the AM mediumwave band is runs from 530kHz to 1610kHz with a channel spacing of 9kHz and in the US it's 520kHz to 1700kHz with a channel spacing of 10kHz.

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You can read the US rules at CFR47, part 15. (Sometimes known as 47CFR15).

If you're using an antenna, section 15.219 would apply (100 milliwatt DC input to the final) with a limit of 3 meters ground, transmission line, and antenna.

If you're using the power line to carry the RF, then 15.221 would apply: 15 uV/m (basically can't hear it) beyond Lambda/2Pi away from wherever that power line goes.

 

If you don't cause interference to radios then nobody will complain and the FCC won't know that you have an illegal transmitter.

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"It is not illegal.... unless you are caught"

Them are words of wisdom right there, i tell you what.

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I believe the only am band that you can transmit on without a liscence is the citizens band. otherwise refered to as "CB". but like everyone else said. if you don't cause interference no one will know. a good place for information would be the arrl

 

A better place for the information would be the fcc, as I wrote before. You can read the US rules at CFR47, part 15. (Abbreviated as 47CFR15). The rules clearly state that it is legal to use the AM band from 520 to 1610 KHz for low power communications.

Further, Citizens Band isn't license free. As with many other frequencies a license is generally required above 100 mW.

 

Not Sure about the USA or Other Countrys.
But "CB in Canada is Licence FREE", as long as you don't Exceed the Legal wattage rating.
"3 Watts Input to the otupt stage and 5 Watts Out".

Low Power AM and FM Transmitters are Also Legal. But I don't have the Precise Specs for these.

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I just looked up 47CFR95; it appears that US has also removed the license requirement for the 11 meter Citizens Band, but you have to use FCC approved equipment.

 

Mind you not only do you have to use licensed bands you have to use licensed hardware. Without a HAM license using any home made transmitter is technically illegal. But that's just the letter of the law. If you don't have the knowledge to pass the written tests on the Amateur Radio Licensing exam you probably shouldn't be playing with electronics in the first place, and after that it makes everything legal and even gives you the ability to use much higher power transmitters on different bands. If it's just a one off or hobby project don't worry yourself about it though as Marks said it's only illegal if they catch you. But you need to be very sure your device is emitting a clean spectrum and not putting out noise on other bands because of a poorly designs circuit, and you're not using excessive power.

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