Re: Analog Cell Phones: Why AM is better than FM - it is not (generally speaking)

In article <1180056431.463704.325710@q19g2000prn.googlegroups.com>,
Radium <glucegen1@gmail.com> wrote:

> > > Why do analog cell phones use FM? Why not AM?
>
> > Do you even know if they do?
>
> Yes. I read about it.
>
> > > Microwave-frequencies can be done in AM just as well
> > > as FM? Why not use AM?
>
> > Why not use FM?
>
> FM is limited to line of sight.

No, this is only related to the frequency range, not the modulation
method. Microwaves (mobile phones etc) are rather similar to light,
short wave transmission bends around buildings, and if you are lucky,
even gets reflected by certain layers of the atmosphere.

> AM provides the ability to converse
> over significantly longer distances than FM.

FM has less noise, as long as the signal is strong vs noise.
You can even improve on that with digital coding (can be used both with
AM and FM), and this is what is typically used with mobile phones.
The advantages with good digital coding are so big, most of our current
transmissions either are already digitally coded or will soon be (eg
analog tv being switched off by the end of the year in Switzerland,
radio to follow in a few years, mobile phones, CD's instead of vinyl,
digital cameras, the internet, etc).

As soon as the signal to noise ratio gets low, FM detoriates rapidly. If
you use digital coding (adding redundant bits to be able to recover from
transmission errors), this effect is even more pronounced.

These are the conditions where AM is better - because of the superior
filtering capabilities of our ear and brain. This is typically the case
on the border of the reception range.

Also bear in mind that receivers differ markedly in their sensitivity,
also in mobile phones (brands, models). Shop around and compare - for
reception quality, range and battery life.

HTH

Marc

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