why FM is preffered for high frequency and AM for low ?????

[wajahat]

Hi all, i know what is FM and AM but i dont know why FM is preffered for high frequency and AM preffered for low frequency .
Any response in this regard would be helpful.
Thanks
Wajahat

 

[IanP]

Re: why FM is preffered for high frequency and AM for low ??

Everything is about bandwidths and about how many channels can exist within dedicated rf bands ..
Without going into technical details, AM channel spacing is ≈10kHz, whereas FM channel spacing is ≈200kHz ..
So, if FM stations were allowed to broadcast in the AM-dedicated-bands (LW or MW), how many channels could function in one area?
Not many ..

Regards,
IanP

 

[Nab]

Re: why FM is preffered for high frequency and AM for low ??

but how about noise.
I think that FM is more stronger then AM which has a lower SNR , doesn't it?

 

[mhtplsh]

Re: why FM is preffered for high frequency and AM for low ??

Before FM radio transmission was in mw & sw. Both were am only. The mw means medium wave which u r calling now am. sw-short wave was upto 30 Mhz,
As technology advanced FM used for transmission. Fm is low noise. Further the bandwidth is more for high quality.
This like LP & CD.

 

[Yahia Muhammad]

Re: why FM is preffered for high frequency and AM for low ??

fm is higher band width than fm so it's used with higher carriers

 

[System.out]

Re: why FM is preffered for high frequency and AM for low ??

Everything is about bandwidths and about how many channels can exist within dedicated rf bands ..

And it is also about transmission power. While AM Spectrum has a delta on the origin, FM(Frequency Modulation) avoids that delta, so it needs less power to transmit. It is hard-difficult-useless-expensive to build an AM power amplifier at FM frequancy band.

Also the channel affects, AM is less tolerant to noise at FM frequencies.

And there are a lot more reasons, that you could learn if you read all about it.

 

[mark123]

Re: why FM is preffered for high frequency and AM for low ??

AM is generally used at lf and FM above 30 Mhz. However CB radio was 27 Mhz AM and when it came to UK it was on FM the main reason for this was that the FM transmittion caused much less interfearence on systems- an old tv or amplifier could easilly pivk up an am cb er several hundered yards away allowing the full audio to be heard. FM would interfear but the audio would not be heard.
FM has a capture ration that AM hasnt- 2 stations on the same frequency if one was several db more powerful than the other fm the strongest one would be heard clearly- am they would both be heard mixed

 

[Borber]

Re: why FM is preffered for high frequency and AM for low ??

The reasons for AM at low and FM at high frequencies are historical. Radio apeared somewhere in twenties and it was AM and at low frequencies maybe because of it's simplicity and technical posibilities. Increasing demands on audio quality has later lead to FM and higher frequencies because of the greater channel bandwidth needed.

 

[betty1007]

FM need more bandwidth than AM , but FM has a better transmission characteristic than AM