Talk:Amplitude modulation
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[edit] Formulas
I am not sure, but as far as I remmber the formulas should be 
and 
so ![\ X_{AM}(t)=[C + M(t)]\cos(\omega_c t)=[C + M \cos(\omega_m t + \phi)]\cos(\omega_c t)](../../../../math/6/2/1/621dd25d8dd8ec0061959896350db399.png)
, i.e., ![\ X_{AM}(t)= C\cos(\omega_ct)+{M \over 2} [\cos(\phi +(\omega_m+\omega_c)t)+\cos(\phi +(\omega_m-\omega_c)t)]](../../../../math/6/e/5/6e5b46447bfe16b961543411b0e46390.png)
, thus, ![\ X_{AM}(t)=C[1+m_a\cos(\omega_mt)]\cos(\omega_ct)](../../../../math/1/1/7/11706c2f0f1df3ac25e097de314b8370.png)
while 
. The first formulas, here in this article, include sines but only the last one include cosines. I scammed the other Wikipedias and I found cosines in every forgin Wikipedia I checked. Am I mistaken? --Shimonnaim 13:25, 31 March 2007 (UTC)
[edit] Image
The FM article uses Image:Frequency-modulation.png as a static image showing the waveform. It seems like it would wise to include the equivalent image for AM on this page: Image:Amplitude-modulation.png. Thoughts? Tacvek 18:20, 29 June 2007 (UTC)
[edit] 'Telephone' example
I don't think that the telephone is a good example. We can't consider a baseband medium 'modulated', even with DC bias, IMO. A better example is needed. Or am I missing a historical AM telephone? --Ktims 07:28, 31 August 2007 (UTC)
- I am inclined to agree. But I will play devil's advocate for a moment. Rather than looking at it as "DC bias" or "transmission medium", the implication is that it is a 0 Hz "carrier", with a measureable power level of its own. Without that power source, the telephone apparently doesn't work.
- In contrast, consider acoustic transmission of the same voice signal through air. The air provides no energy. It is truly just a medium. The only measureable power comes from the information source itself.
- But I agree that the distinction is unnecessarily subtle.
- --Bob K 14:17, 31 August 2007 (UTC)
[edit] amplitude modulation index
I don't think the amplitude modulation index is correctly explained.
See http://www.rfcafe.com/references/electrical/amplitude_modulation.htm —Preceding unsigned comment added by 192.91.172.36 (talk) 02:08, 2 October 2007 (UTC)
I agree the calculation for the modulation index is obviously wrong because earlier it the article it is explained that A=0 is used for carrier suppression. This equation therefore implies that m = M/0 = infinity when the carrier is suppressed.
Kris —Preceding unsigned comment added by 203.97.235.82 (talk) 07:49, 8 February 2008 (UTC)
