please

Discussion in 'General Electronics Chat' started by mute2, Nov 29, 2007.

  1. mute2

    Thread Starter New Member

    Aug 28, 2007
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    Please i want make comparing between FM and AM and which is better to use?
     
  2. eeboy

    Active Member

    Sep 27, 2007
    90
    1
    For what purpose?

    What country? Most countries have laws regarding RF communications.
     
  3. cumesoftware

    Senior Member

    Apr 27, 2007
    1,330
    10
    AM is easier to demodulate. You can build a simple AM receptor with very few components (a germanium diode, a coil as antenna and a headphone set).
     
  4. Eplanet

    Active Member

    Oct 25, 2007
    42
    0
    hi
    FM have high quality but for small distance and AM have bad quality but for long distance.
    because FM is Frequency Modulation and AM is amplitude Modulation.
    you can filtering FM for better quality but you cant filtering AM waves because with this work you eliminating All AM waves.
    in my idea for small distance and normal purpose FM is better.
     
  5. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    FM is line-of-sight only. The upper atmosphere does not reflect the higher frequency FM signals. Once over the horizon, FM is no good. AM will reflect and bounce around the whole world.

    FM signals require more bandwidth than AM signals.
     
  6. Papabravo

    Expert

    Feb 24, 2006
    10,164
    1,797
    Ahh...this is a picky point but the modulation technique used has absolutely nothing whatsoever to do with propagation characteristics. It is soley a function of frequency. For example Air Traffic Control uses AM on the band from 118 MHz. to 136 MHz. Those transmissions are also line of sight. It just so happens that at 40,000 ft. you get a pretty good line of sight.

    FM transmission is not commonly used below the 10M band at about 29.5 MHz. because the bandwidth required is a pretty large fraction of the available space.

    Nobody even mentioned SSB transmissions which are the prefered method of voice communication in the 1.6 MHz. to 30 MHz. range.
     
  7. Eplanet

    Active Member

    Oct 25, 2007
    42
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    ssb is for radio police and it is illegal
     
  8. Dave

    Retired Moderator

    Nov 17, 2003
    6,960
    145
    It is clear from the answers given that the definition of "better" is subjective and determines the answer. Can you define "better" in the context of your question?

    Dave
     
  9. Papabravo

    Expert

    Feb 24, 2006
    10,164
    1,797
    That is not true. Police VHF radios use narrow band FM. SSB is certainly legal on all of the Amateur Bands that I enjoy operating on. You are correct that it is illegal to operate with any modulation mode on the Police Radio Bands
     
  10. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
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    We used a lot of SSB when I was in the Navy. Does this mean that all of the sailors are going to be arrested?:eek: AGAIN?!:eek::D
     
  11. Nomad

    Active Member

    Oct 21, 2007
    43
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    ssb is also used on cb radios. you know that "breaker breaker good buddy thats a big 10-4" stuff you see on tv and in movies. yes i know cb's primarily am, truckers dont talk like that, and ham operators usually despise people like me who modify their cb's to listen in on their 10 meter beeping. j/k
     
  12. GS3

    Senior Member

    Sep 21, 2007
    408
    35
    Use for what? Each has its uses, its pros and its cons.

    This is just a silly, meaningless, assertion. More interesting are illegal numbers.

    I will start by agreeing with your overall point. It bugs me when people who know little say things like "NTSC is 60 Hz and PAL is 50 Hz" when in truth PAL and NTSC are color coding schemes which have absolutely nothing to do with frame frequency. Just because most 50 Hz systems use PAL does not mean you cannot use NTSC.

    Similarly, people, including in this thread, are wrongly associating characteristics to the modulation system which they should be associating with band and frequency.

    Having said that, sometimes certain modulation form will be more effective than the other due to several factors like the fact that in AM all the side frequencies may not transmit equally over the reflections in the atmosphere.

    This is not a simple question where one can say one system is better than another. There are multitude of modulation systems and they each have their strong points. If we are restricted to comparing AM and FM I would say AM makes more efficient use of bandwidth but is more subject to noise interference than FM.

    For more info on modulation check out http://en.wikipedia.org/wiki/Modulation
     
  13. JoeJester

    AAC Fanatic!

    Apr 26, 2005
    3,373
    1,159
    SSB is still used, not as much as before though.

    Sailors and dogs keep off the grass Signs on lawns at an earlier time in Norfolk.
     
  14. Papabravo

    Expert

    Feb 24, 2006
    10,164
    1,797
    Niether one can read so what's the point of the sign? Ahhh...cha..cha..cha
     
  15. JoeJester

    AAC Fanatic!

    Apr 26, 2005
    3,373
    1,159
    That is a question for those who posted the sign on their lawn. :)
     
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