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And although we haven’t talked yet about sampling and the associated artifacts, basically, as we’ll see in the upcoming lectures, in order to sample a wave form and convert it into digital form, it requires that the wave modulation pdf download first be low pass filtered.
And, in fact, we can flip modulation pdf download cursor on modulafion I happen to just magically have it positioned correctly.
And in that case, the modulation pdf download were all scaled up by a factor of 2. Modulation pdf download red lead here is a ground. And this will act as the antenna. Might be interesting, Al, to go and look at a richer set of signals, such as the triangle wave and the square wave– things modu,ation are conveniently on the signal generator itself.
AMPLITUDE 01 download – 2shared
And that will be the signal that will be modulated, according to the carrier. But maybe we can begin just with the modulation pdf download generator. And Sandy, I’d really like to thank you for joining us, for sharing your insights with us, as well as sharing your equipment with us.
OK, now, modulation pdf download can change also the carrier frequency and, as Sandy’s indicated, various parameters. And let’s position the cursor on the frequency of the sine wave.
modulation pdf download And what we had done there was to record a modulation pdf download glockenspiel note, and then we played that back at half speed. And these side bands then correspond to dowmload side bands associated with the modulating signal. And so here the power transmitted required is higher, but the demodulator, based on using an envelope detector, is considerably simpler. And so this is the spectrum then of the original glockenspiel note.
Another thing we can do is to vary the frequency of the sinusoidal signal that’s modulating it. Now you haven’t seen any change on this particular displaybut let me change the frequency scale.
And also, we can change the wave shape itself from a sine wave to a triangle modulation pdf download and you notice that has a richer sound to it– and then finally to a square wave, which is an even brighter sound.
And I can switch to square wave– doesn’t look much modulahion a square wave.
So what we’re computing, of course, modulation pdf download samples of the Fourier transform. Moving over towards the left, we can change the DC offset which varies the signal, the level upon which the signal rides. And those harmonics will go away when doownload go back to a sinusoidal carrier. And, once again, you see that the time wave form over here has been scaled by a factor of modulation pdf download. And so the modulated output can have a variable pdd modulation– the percent modulation being changed, depending on how we set this variable gain.
I’ll give it a little bit more game.
And actually, as you realize from the previous lectures, with the triangle and square wave with the same fundamental modulation pdf download the sine wave, the richness comes in modulation pdf download of the higher harmonics in the Fourier series representation. Here we have the first spectral line. Make some adjustments there. Those are the side bands due to the square wave modulation. And this is the signal into the envelope detector, in this particular radio.
It computes the Fourier transform or the spectrum. And this is the actual intermediate frequency, modulated by the audio.
I’ll switch over to a square wave now. I set this up so that what’s coming into my microphone modulation pdf download indeed what you’re going to see on the two screens.
And in fact, a envelope detector of the type that we’ve talked about before is exactly what is used in AM radios, modulaton of the fact that it’s so inexpensive. OK, let’s look quickly at the various buttons downnload. And this is the frequency modulation pdf download of the sine wave.
This is the third harmonic, fifth harmonic, et cetera. And just to point out, again, the fact that modulation pdf download sine wave spectrum, of course, is just a single line corresponding to the fundamental frequency. And we can dpwnload out, in fact, that it’s cycles. Now I’ve modulation pdf download this up so it’s tuned to a particular radio station, and I hope I can find it now.
And then you simply filter out the higher order harmonics. There’s significant distortion, because of all the downolad that the signal is going through. And what you see is modulation pdf download the harmonics coming up, being displayed. And there are modulatoon ways of controlling it. And of course, the fifth. One is the wave form of the carrier itself– and this is typically sinusoidal in the broadcast industry, but others are interesting to look at as well.
And having the equipment that we have here gives modulation pdf download kind of a nice opportunity to do that. This is coming from the signal generator up here.
While you do that, let me just position the cursor modulation pdf download I can on the sine wave. OK, and it’s really kind of interesting and dramatic We’ll look at a block modulation pdf download of the spectrum analyzer shortly, but first let’s just look at a few quick things to get a feel for downpoad. And Sandy, maybe you could just give us a quick tour of what we have here. OK, I’ll make the frequency higher.