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I am building an FM transmitter. It is going to be designed to transmit only for a short range of around 50 to 100 meters. My question is whether it is illegal to transmit signals in the FM band over this short range without owning a license? If yes, what should I do to test it?

P.S. I live in India.

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  • \$\begingroup\$ dunno about India, but in the U.S., you can get away with it if the transmitter is less than 100 mW. the signal will not get far, probably less than 200 meters. \$\endgroup\$ – robert bristow-johnson Nov 28 '15 at 6:09
  • \$\begingroup\$ Try the Telecom Regulatory Authority of India here. \$\endgroup\$ – EM Fields Nov 28 '15 at 6:22
  • \$\begingroup\$ I can't get 40 feet / 9 meters on a commercial fcc authorized personal fm transmitter in the us. Let alone double or triple digit meters. \$\endgroup\$ – Passerby Nov 28 '15 at 6:46
  • \$\begingroup\$ I don't get you. Can you please elaborate? \$\endgroup\$ – Sâu Nov 28 '15 at 6:50
  • \$\begingroup\$ @Passerby, you're probably right. long ago i had a walkie-talkie that was about 30 Mhz and 100 mW (but it was AM, not FM, but that should matter less, IMO) and we could get it to work for about 1/8 mile. \$\endgroup\$ – robert bristow-johnson Nov 28 '15 at 6:52
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Different locations will have different rules. If you live in India, check the regulations for India.

Generally, powerful transmissions in licensed bands like FM audio must be licensed, to prevent interference with other users. If other users complain, you may get tracked down, and your equipment confiscated or destroyed.

Most places have unlicensed bands as well, like the so called ISM frequencies, and usually a few other bands for other purposes as well, like garage door openers and short range personal comms.

If your transmitter is very low power, and operated at times and at frequencies when it could not interfere with any stations your neighbours in range are tuned to, then you can probably figure out what the actual chances of causing trouble or getting caught are.

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