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desperado1
Joined: 04 Sep 2006
Posts: 194
Helped: 6
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 05 May 2009 9:09 am broadcast radiated power |
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| What is the power levels of AM and FM broadcast ?
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hakeen
Joined: 16 Jun 2005
Posts: 153
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05 May 2009 15:56 Re: what is the power of AM and FM broadcast ? |
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Hi
For AM/FM in USA, you can refer to FCC page.
MINIMUM POWER LEVELS for LICENSED BROADCAST OPERATION
The minimum power for a standard FM broadcast station which a construction permit applicant may request is 100 watts (0.100 kilowatts). Alternatively, if an effective radiated power of less than 100 watts is sought, the combination of the proposed effective radiated power and antenna height above average terrain must cause the distance to the predicted 1 millivolt per meter (mV/m) contour (or 60 dBu contour) to be greater than 6 km. See 47 C.F.R. Section 73.211 of the Commission's Rules. Please note that new FM stations will not be authorized to operate with less than these minimums. While there are a few Class D FM noncommercial educational stations (also called "10 watt stations") which are permitted to continue operations with smaller facilities, authorizations for new Class D FM stations were discontinued in 1978. No new Class D FM stations will be authorized outside the state of Alaska. See our Information Sheet about How To Apply For A Broadcast Station for additional information on application preparation.
Stations authorized in the new LPFM service will operate with effective radiated powers (ERP) between 1 watt (0.001 kW) and 100 watts (0.100 kW). In any case, the distance to the 1 mV/m (60 dBu) contour from an LPFM station or application will not be permitted to exceed a reference distance of 5.6 km. LPFM applications which would require operation with less than 1 watt ERP will not be accepted for filing.
The minimum power for an AM broadcast station which a construction permit applicant may request is 250 watts (0.250 kilowatts). Alternatively, if an effective radiated power of less than 250 watts is sought, an equivalent RMS value of at least 141 millivolts per meter (mV/m) at a distance of 1 km from the tower site must be proposed. See 47 CFR Section 73.21(a)(2) of the Commission's Rules. No AM broadcast station will be authorized with less than these minimums. See our Information Sheet about How To Apply For A Broadcast Station for additional information on application preparation.
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desperado1
Joined: 04 Sep 2006
Posts: 194
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06 May 2009 2:43 what is the power of AM and FM broadcast ? |
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Thanks for the answer .......................it was awesome........
I have one more query. Why is the range of AM transmission greater than the FM ?
Also Why the FM transmits at higher frequencies than AM ? Is it possible to transmit FM signals at lower frequencies ?
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Kral
Joined: 28 Mar 2005
Posts: 1182
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06 May 2009 18:00 Re: what is the power of AM and FM broadcast ? |
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desperado1,
Regarding your 20:43 reply: AM signals travel farther because of the lower carrier frequency. It has nothing to do with the modulation type. FM transmission uses higher carrier frequencies because the FM scheme inherently produces a wider sideband bandwidth. Theoretically, the sidebands extend to infinity, although in real world applications the bandwidth is limited. If a lower carrier frequency were used, the sidebands would occupy a higher percentage of the assigned spectrum.
Regards,
Kral
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desperado1
Joined: 04 Sep 2006
Posts: 194
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08 May 2009 2:54 Re: what is the power of AM and FM broadcast ? |
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| thanks for the reply. i.e. can we use the lower frequencies in FM to achieve greater distance ? Why the FM has inherently wider bandwidth ? Is it because of it's higher frequency usage ?
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Kral
Joined: 28 Mar 2005
Posts: 1182
Helped: 187
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19 May 2009 19:46 Re: what is the power of AM and FM broadcast ? |
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desperado1,
FM inherently occupies a wider bandwidth because, unlike AM, the carrier frequency deviation depends on the amplitude of the mudulating signal, not the frequency of the modulating signal. The frequency deviation is described by a series of Bessel functions. As the first reference shown below graphically illustrates, the deviation theoretically extends to infinity, depending on the amplitude of the modulating signal.
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Contrast the FM sidebands with the AM sidebands. Take for example the case where the carrier is amplitude modulated by a single sine wave of frequency fm. Let the carrier frequency = fc. The only sidebands present are the frequencies (fc + fm) and (fc - fm).
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The references below illustrate the properties of frequency modulation.
Regards,
Kral
Added after 1 minutes:
Oops! I forgot to include the references. Here they are:
http://cnyack.homestead.com/files/modulation/modfmbs.htm
http://en.wikipedia.org/wiki/Frequency_modulation
http://www.st-andrews.ac.uk/~www_pa/Scots_Guide/RadCom/part12/page1.html
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