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Diode laser FM/AM modulation

Started by George Herold February 9, 2017
On 10.2.17 16:24, George Herold wrote:
> On Friday, February 10, 2017 at 8:05:03 AM UTC-5, Tauno Voipio wrote: >> On 9.2.17 19:39, George Herold wrote: >>> >>> Hmm can I ask a silly radio question. If I've got >>> (say) 50% AM, modulation index = 0.5, how big are the side bands compared >>> to the central carrier? (I guess I should be able to go look that up somewhere.) >>> (Or measure it myself) >>> >>> I could then go measure the AM MI for the laser and get some number. >>> >>> George H. >> >> >> There's no such thing as modulation index in AM. MI belongs to >> angle modulation (PM, FM). >> >> An AM signal modulated with a single sine wave is >> >> AM(t) = A(1 + M cos(omega_m t)) cos(omega_c t), >> >> where >> >> A = carrier amplitude >> M = modulation depth (0 .. 1) >> omega_m = modulation signal angle frequency >> omega_c = carrier signal angle frequency >> t = time. >> >> The expansion of the expression and cranking out the sideband >> signals from the cos(omega_m t) cos(omega_c t) is left as homework. >> >> -- >> >> -TV > > Right, Thanks Tauno. (I scribbled down the math...(I missed the 1+ term.. > so thanks for that.) > > I should let you all know that when I post questions like this, I'll often > send a link to whomever asked me the question... saves me having to repeat > what others say here. > > A quote from my last customer. > > "cheers George - impressive backup you have there! " > > I just wanted to second that! > > George h. >
If you leave the 1+ away, you'll get what is called DSB-SC or, with square wave modulation, BPSK. -- -TV