Interference Levels

National authorities are responsible for setting levels and enforcing them, and acceptable transmission varies from country to country. Transmitting equipment is therefore covered by national licences, and the licensing authority will set up the constraints under which transmission is lawful.

For example, using the 27MHz amplitude-modulated Citizens Band equipment designed for use in the USA is unlawful in the UK and users can be prosecuted. The UK has a 27MHz frequency-modulated Citizens Band service, and usable equipment is stamped 27/81 in a circle on the front, the 81 standing for 1981, the year the service was standardised. There is a slight overlap between the bands, though that part of the 27MHz spectrum used in the USA for AM CB is partly used for remote control systems in the UK; unlawful use of CB equipment in remote control frequencies exposes risk to life and limb were the remote control to be servicing, say, a powered model aircraft, which is why enforcement is necessary.

So the actual power levels, SNR, interference etc are therefore locally regulated in each country? Which means inter-operability across different countries may cause an issue?

It may, though it rarely does, as use of the electromagnetic spectrum for radio communication is regulated by international treaties.

http://en.wikipedia.org/wiki/Transmitter

http://en.wikipedia.org/wiki/Radio_spectrum

That is true. Thanks

Common items such as marine, aircraft and amateur are more or less trans national. Cellular to a lesser extent. The rest of the spectrum is allocated among various services, AM & FM commercial radio, military and government, railroad, police and fire etc. Each of these entities have power, bandwidth, and spectrum limitations. Along our Canadian border, further restrictions apply. These change over time, e.g. UHF Television used to be 470 MHZ to 800 MHZ Channels 14 to 83 has been re-farmed to other users.