Amplitude modulation -- misnamed?
in [DSP]
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From: Steve Pope on 2 May 2010 02:07 Shouldn't amplitude modulation really be called "Magnitude Modulation"? After all, in FM, the amplitude is still being modulated, but the magnitude is constant. Or maybe I have too much time on my hands. S.
From: Rune Allnor on 2 May 2010 03:35 On 2 Mai, 08:07, spop...(a)speedymail.org (Steve Pope) wrote: > Or maybe I have too much time on my hands. ....maybe... Rune
From: glen herrmannsfeldt on 2 May 2010 03:52 Steve Pope <spope33(a)speedymail.org> wrote: > Shouldn't amplitude modulation really be called "Magnitude > Modulation"? > After all, in FM, the amplitude is still being modulated, but > the magnitude is constant. When I learned it, in the expression A*sin(wt+b) A is the amplitude, w the angular frequency and b the phase offset. There are also expressions like "for the coherent case, add amplitude, for the incoherent case add magnitude." The magnitude, then, is proportional to A**2. So it seems to me that for radio, where the signal is coherent, it is amplitude modulation, but for optical communication, such as in optical fibers, it should be magnitude modulation. (Even for diode laser source, two sources aren't usually coherent with each other, and the coherence length and coherence time aren't all that long.) -- glen
From: Tauno Voipio on 2 May 2010 04:08 On 2.5.10 9:07 , Steve Pope wrote: > Shouldn't amplitude modulation really be called "Magnitude > Modulation"? > > After all, in FM, the amplitude is still being modulated, but > the magnitude is constant. Would you please explain. The creation of sidebands does not change the amplitude of the combination of carrier and all sidebands in FM. AM for sinusoidal modulation: f(t) = A*(1 + M*cos(omega_m*t))*cos(omega_c*t) FM for sinusoidal modulation: f(t) = A*cos(omega_c + d*cos(omega_m*t)) Asterisks (*) are for plain old multiplication. The amplitude of the FM signal is constant A. -- Tauno Voipio (MSEE, OH2UG) tauno voipio (at) iki fi
From: Magnum on 2 May 2010 04:16
"Steve Pope" <spope33(a)speedymail.org> wrote in message news:hrj4qa$j1e$1(a)blue.rahul.net... > Shouldn't amplitude modulation really be called "Magnitude > Modulation"? > After all, in FM, the amplitude is still being modulated, but > the magnitude is constant. Both signals, the modulating signal and the transmitted signal are broadly cisoidal in nature and have an amplitude, or magnitude, depending on how you choose to call it. You seem to want to restrict the use of amplitude to refer to the modualting signal and the use of magnitude to refer to the transmiited signal, when either term can legitimately be used for either signal. |