How to get envelope from AM signal without phase shift
in [DSP]
|
Prev: How Rune Allnor can attend the COMP.DSP Conference
Next: Inertial navigation (anyone familiar with this stuff here?)
From: WWalker on 2 Apr 2010 17:12 Eric, Do you accept now that the low pass filtered random signal I used in my simulation could be the information in certain experimental setups? For example, this band limited signal could be created directly, for instance, by slowly manually adjusting a variable voltage source. Each voltage point on the voltage vs time curve of the voltage source is information about what the voltage is at that time. Another possibility would be to record the low pass filtered random signal and just play back the signal during the transmission. William >On 4/1/2010 5:51 AM, WWalker wrote: >> Eric, >> >> I appreciate this discussion and I do understand the points all of you have >> been making very clearly. I teach advanced analog and digital signal >> processing, mathematics, as well as RF technique, and EM theory, and I have >> been looking at this problem for 20 years. I simply do not agree with some >> of the conclusions in this discussion for very logical reasons. >> >> I think maybe the problem is that we are all having difficulty >> understanding what is the information in the simulations being discussed, >> where is it located, and how does it propagate. Information is not well >> understood and I think it needs to be discussed to see if it can be defined >> better, as it applies to these simulations. > >> As I mentioned before, I agree that if the information is the edge of a >> sharp pulse, which is passed through a narrowband nearfield dipole AM >> transmission and detection system, then the time delay will be the time >> delay of the narrowband filter plus the freespace propagation time of the >> pulse edge, which propagates at speed c in both the nearfield and farfield. >> The pulse will distort in the nearfield but the edge will be clearly >> defined and can be used to trigger a bomb. With this type of setup, the >> overall time delay of the pulse edge will clearly be less than a light >> speed time delay. > >> But, if the information signal is directly input, bandlimited, in a >> narrowband nearfield dipole AM transmission and detection system, then the >> time delay of the bandlimited signal will only be the freespace propagation >> delay, which is less than light speed as shown in my simulations. > >I think you have not shown that. There is another, more likely, >explanation. Unless and until the more likely explanation is disproven >I think it is impossible to claim propagation faster than c. > >At least two fairly simple ways to further illuminate the issue have >been mentioned (interruption of the signal and measurement of initial >onset of energy from the zero state). I'm curious as to why you don't >seem interested in pursuing them. > >> For example, if the signal is created by a voltage source that is manualy >> slowly adjusted, and if the signal is then mixed with a carrier and sent >> though a nearfield dipole system, then the detected envelope will arrive >> undistorted earlier than a light propagated signal, as I showed in my >> simulations. Each voltage point on the voltage vs time curve of the voltage >> source is information about what the voltage was at that time. If that >> pattern is reproduced exactly a distance away, then the time delay of each >> information voltage point is the propagation time of the information. > >Except that such a signal is easily predicted, without accelerated >propagation, by certain practical processes, and that prediction is >easily mistaken for non-causality, time travel, or accelerated >propagation (as you seem to have done). Again, a couple simple >experiments may help show the difference. > >Your "accelerated" signals are well within the believable realm of phase >advance achieved by a bandlimited prediction process. I haven't noticed >you take any steps toward eliminating that explanation. Until you do, >expect skepticism and/or dismissal from many. > >-- >Eric Jacobsen >Minister of Algorithms >Abineau Communications >http://www.abineau.com >
From: Jerry Avins on 2 Apr 2010 17:34 On 4/2/2010 5:12 PM, WWalker wrote: > Eric, > > Do you accept now that the low pass filtered random signal I used in my > simulation could be the information in certain experimental setups? I'm not Eric, but no. > For example, this band limited signal could be created directly, for > instance, by slowly manually adjusting a variable voltage source. Each > voltage point on the voltage vs time curve of the voltage source is > information about what the voltage is at that time. I suppose so, but remember: random is not the same as arbitrarily chosen. If the signal represents information -- a winner at Belmont, say -- the time to construct the apparently low-passed signal will be no less than running an impulse through an actual filter. So what is gained? > Another possibility would be to record the low pass filtered random signal > and just play back the signal during the transmission. Then consider the time to play back the prerecorded signal after the decision to transmit it is made. This buys nothing. ... Jerry -- "It does me no injury for my neighbor to say there are 20 gods, or no God. It neither picks my pocket nor breaks my leg." Thomas Jefferson to the Virginia House of Delegates in 1776. ���������������������������������������������������������������������
From: Eric Jacobsen on 2 Apr 2010 17:45 On 4/2/2010 2:12 PM, WWalker wrote: > Eric, > > Do you accept now that the low pass filtered random signal I used in my > simulation could be the information in certain experimental setups? What do you mean by "the" information? What information? > For example, this band limited signal could be created directly, for > instance, by slowly manually adjusting a variable voltage source. Each > voltage point on the voltage vs time curve of the voltage source is > information about what the voltage is at that time. > > Another possibility would be to record the low pass filtered random signal > and just play back the signal during the transmission. > > > William The point is that ANY bandlimited signal, regardless of how much 'information' is in it, can be predicted by practical processes (e.g., a filter with negative group delay) in a manner that looks exactly like the phase advance you're seeing. You claim it reveals accelerated propagation, but it is more easily explained by mere bandlimited prediction. I see no significant difference between your plots and the plots on Andor's blog. See Andor's Fig. 4 or Fig. 6. The prediction mechanism may be somewhat different in your case (or it may not, I think of whatever your simulated process is as a black box), but the result is indistinguishable. I don't think you can claim accelerated propagation until you demonstrate that what's happening is not just bandlimited prediction. I've tried to make this point many times, and even suggested means by which you might try to disprove bandlimited prediction, but you seem to ignore all of that. I recently explained that the bandlimiting you're performing arguably spreads the information out over a time period which is essentially equal to the impulse response length of the bandlimiting process. This is what makes the signal predictable over a small time window, and it also makes it difficult to claim accelerated propagation when the time delta in question is a small fraction of the length of the impulse response. I pointed out a while back that the time advance you're claiming is less than a three degree phase advance at the highest frequency of the bandlimited pulse. That's a pretty small advance, and the fact that it is much smaller than the length of the pulse suggests that there is no chance that any sort of non-causality is involved. The pulse spreading over time also makes it hard to make any claims about differences in propagation times when the differences are much smaller than the pulse length. Unless and until you can demonstrate clear propagation of a triggering event (not explainable by bandlimited prediction), measured from the event itself (not a bandlimited version where the information has been spread out over time) that is explainable by no other means that exceeding c I don't think you can claim that that is the explanation. From my perspective you have a long way to go, but that doesn't seem to stop you from making the claims, anyway. Yet again, I've already mentioned, as have others, ways to try to clear this up. Your apparent reluctance to try them is likely to be interpreted by many as indicative that the more likely explanation of bandlimited prediction prevails. -- Eric Jacobsen Minister of Algorithms Abineau Communications http://www.abineau.com
From: WWalker on 2 Apr 2010 18:23 Jerry, Lambda refers to the farfield where: lambda*f = c . I am just using it as a reference distance to differentiate nearfield (<Lambda) and farfield (>Lambda). c also refers to the farfield speed. When the photon gets say 10*Lambda away from the source: dt=10*Lambda/c then dE*dT =10*hdv/c =h therefore: dv= c/10, so v=c+dv = 1.1*c When the photon is only 1/10*lambda away from the source: dt=1/10*Lambda/c then dE*dT=1/10*hdv/c =h therefore: dv= 10c ,so v=c+dv = 11*c William >On 4/1/2010 6:22 AM, WWalker wrote: >> Jerry, >> >> In my last post (argument pasted again below) I presented an analysis which >> showed in the nearfield dv>>c in the nearfield and dv<<c in the farfield. >> Once the photon is created, it is propagating in one direction away from >> the creation point with, lets assume, a possitive velocity. Lets say in the >> nearfield dv=10c therefore, the velocity of the photon will range between: >> 0-10c, with an average of 5c, which is much faster than light. >> >> "Lets calculate the uncertainty of the velocity of a photon that >> propagates >> one wavelength after it is created: According to the Heisenberg >> uncertainty >> principle, the relation between the uncertainty in Energy (dE) and the >> uncertainty in time (dt) is: dE*dt>= h. The time for a photon to cross >> one >> wavelength distance is: dt = lambda/c. Since dE = h*df and df=dv/lambda >> then dE*dt=h*dv/c, but dE*dt<= h therefore: dv>= c >> For smaller distances the uncertianty will be greater and for larger >> distances the uncertainty will be much smaller. >> " > >That argument has a certain amount of plausibility at first hearing, but >it raises some questions. How far does the photon get from its source >before the velocity uncertainty becomes very small? What justifies the >assumption of one wavelength? After all, as the photon's energy varies, >so does its wavelength. > >You wrote dt=lambda/c. shouldn't that be t=lambda/c? When dt/t is much >greater than unity (you picked 10 in your example) can we still write in >terms of differentials? > >Jerry >-- >"It does me no injury for my neighbor to say there are 20 gods, or no >God. It neither picks my pocket nor breaks my leg." > Thomas Jefferson to the Virginia House of Delegates in 1776. > >
From: Jerry Avins on 2 Apr 2010 19:12
On 4/2/2010 6:47 PM, WWalker wrote: > Jerry, > > Think of a transformer, which could be a magnetic transmitter dipole > coupled to a nearfield recieving magnetic dipole. If a resistor is put > across the receiver dipole then power is drawn from the source, transmitted > by the magnetic field, and then absorbed by the resistor. If no fields are > reflected by the receiver dipole then it does not alter the incomming > field. OK: a transformer. Most transformers are used with essentially constant voltage on the primary. As such, a load on the secondary hardly affects the field. After all, the primary voltage is n*d(phi)/dt, where n is the number of turns and phi is the flux. If the secondary load is not to affect the primary current, you must excite the primary with a constant-current source. The magnetic field will then droop with load. ... Jerry -- "It does me no injury for my neighbor to say there are 20 gods, or no God. It neither picks my pocket nor breaks my leg." Thomas Jefferson to the Virginia House of Delegates in 1776. ��������������������������������������������������������������������� |