In Reply to: Re: Ah, jj! posted by morricab on June 21, 2006 at 01:43:27:
Digital is not poor capturing signals that are close to Nyquist, AS LONG AS THEY DON'T GO OVER NYQUIST.But when you vary a signal "close to nyquist" you expand its bandwidth, and you go OVER fs/2 in real spectrum.
Do not forget that the only zero-bandwidth signal is an infinitely long sine wave.
Even a switched sine wave has a heavily spread spectrum. That's all it takes. All. It. Takes.
Btw, I suspect this is a prophead subject. It involves understanding the duality theorem, for instance, to see how mulitplying in the time domain convolves spectra in the frequency domain (never mind what some people seem to think).
This post is made possible by the generous support of people like you and our sponsors:
Follow Ups
- Um, no. - real_jj 06/21/0610:41:04 06/21/06 (52)
- Re: Um, no. - morricab 02:28:03 06/22/06 (3)
- Well, the "how' is not hard to understand. - real_jj 12:14:03 06/22/06 (2)
- Re: Well, the "how' is not hard to understand. - morricab 06:04:01 06/23/06 (1)
- Hm, not sure where to start... - real_jj 10:56:12 06/23/06 (0)
- Not true - Christine Tham 17:40:04 06/21/06 (42)
- Instantaneous freq of FM signal vs Fourier spectrum - andy_c 06:55:38 06/24/06 (0)
- Re: Not true - Todd Krieger 21:39:39 06/21/06 (17)
- Again, you fail to realize... - real_jj 22:18:36 06/21/06 (16)
- I Don't Think That's the Case..... - Todd Krieger 23:09:51 06/21/06 (15)
- whatever you think of wikipedia - tunenut 10:27:16 06/22/06 (4)
- I Still Don't Think It's the Case..... - Todd Krieger 13:40:46 06/22/06 (2)
- did you read the link? - tunenut 14:02:59 06/22/06 (1)
- Did you see where he denied that the sinc function can be applied in frequency? - real_jj 14:17:07 06/22/06 (0)
- link - tunenut 10:31:10 06/22/06 (0)
- No, Todd, the "period" that the sum repeats at can be "infinity". - real_jj 10:21:23 06/22/06 (9)
- Re: No, Todd, the "period" that the sum repeats at can be "infinity". - Todd Krieger 13:54:18 06/22/06 (8)
- Stop denying the obvious, Todd. Go study the delta function. GO DO THE WORK! - real_jj 14:13:12 06/22/06 (7)
- Context..... - Todd Krieger 15:32:22 06/22/06 (6)
- You say: Granted for general Fourier analysis.... - real_jj 15:51:40 06/22/06 (5)
- Re: You say: Granted for general Fourier analysis.... - Todd Krieger 16:46:58 06/22/06 (3)
- No, Todd, that's not what I think they would say... - real_jj 16:54:46 06/22/06 (2)
- Do a Google Search.... - Todd Krieger 17:04:08 06/22/06 (1)
- Do a google search on "delta function", Todd... - real_jj 17:15:55 06/22/06 (0)
- Oh, and ... - real_jj 15:54:44 06/22/06 (0)
- Totally, absolutely wrong, Christine! - real_jj 19:58:54 06/21/06 (8)
- Again, a little less arrogance would perhaps be advisable - Christine Tham 20:18:42 06/21/06 (7)
- Let's see, is it arrogant to announce completely incorrect things in public? - real_jj 22:03:59 06/21/06 (6)
- OK, this is my final post - Christine Tham 03:22:08 06/22/06 (5)
- Re: OK, this is my final post - Dave Kingsland 10:16:42 06/22/06 (3)
- Re: OK, this is my final post - Christine Tham 17:32:19 06/22/06 (1)
- Tsk. You've embarrassed yourself, now you add insult to injury - real_jj 17:52:46 06/22/06 (0)
- Exactly. - real_jj 10:45:20 06/22/06 (0)
- You've taken things completely out of context. - real_jj 10:09:48 06/22/06 (0)
- strange statement - tunenut 19:21:21 06/21/06 (13)
- You'll find sidebands at the modulation spectrum/frequencies... - real_jj 20:01:38 06/21/06 (12)
- This is just absolutely irrelevant - Christine Tham 20:43:33 06/21/06 (11)
- Yes, I certainly have done Fourier analysis of a chirp. - real_jj 22:04:58 06/21/06 (0)
- why don't you just do a frequency analysis? - tunenut 20:54:24 06/21/06 (9)
- What makes you think I haven't? - Christine Tham 21:05:58 06/21/06 (8)
- Re: What makes you think I haven't? - andy_c 09:12:01 06/24/06 (0)
- questions - tunenut 08:52:06 06/22/06 (5)
- Re: questions - Christine Tham 17:46:05 06/22/06 (4)
- I was with you up to the last sentence - tunenut 18:07:43 06/22/06 (2)
- Re: I was with you up to the last sentence - Christine Tham 18:14:17 06/22/06 (1)
- And, of course, as the window gets shorter, - real_jj 21:10:44 06/22/06 (0)
- Sigh. - real_jj 17:54:04 06/22/06 (0)
- And, then, you assert a problem with sampling. - real_jj 22:05:54 06/21/06 (0)
- Here We Go Again..... - Todd Krieger 11:01:58 06/21/06 (4)
- Re: Here We Go Again..... - andy_c 19:38:48 06/23/06 (0)
- FYI..... - Todd Krieger 11:43:07 06/21/06 (1)
- That's good, Todd, that's part of what happens... - real_jj 13:06:47 06/21/06 (0)
- I see you're still misteaching. GET LOST - real_jj 11:31:30 06/21/06 (0)