please

bloguetronica

Joined Apr 27, 2007
1,372
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).
 

Eplanet

Joined Oct 25, 2007
42
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.
 

thingmaker3

Joined May 16, 2005
5,084
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.
 

Papabravo

Joined Feb 24, 2006
12,767
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.
 

Dave

Joined Nov 17, 2003
6,970
Please i want make comparing between FM and AM and which is better to use?
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
 

Papabravo

Joined Feb 24, 2006
12,767
ssb is for radio police and it is illegal
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
 

Nomad

Joined Oct 21, 2007
43
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
 

GS3

Joined Sep 21, 2007
408
Please i want make comparing between FM and AM and which is better to use?
Use for what? Each has its uses, its pros and its cons.

ssb is for radio police and it is illegal
This is just a silly, meaningless, assertion. More interesting are illegal numbers.

Ahh...this is a picky point but the modulation technique used has absolutely nothing whatsoever to do with propagation characteristics.
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
 

JoeJester

Joined Apr 26, 2005
4,130
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.
 
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