How to get envelope from AM signal without phase shift
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From: Jerry Avins on 22 Mar 2010 11:14 Rune Allnor wrote: ... > The spatial phase you talk about should be measured at 550 MHz, > which is the signal that actually propagates down the physical > channel. From what has been written, the signal is ordinary double-sideband AM. Make that 450 *and* 550 MHz, as I wrote at 10:04 (my time). ... Jerry -- Discovery consists of seeing what everybody has seen, and thinking what nobody has thought. .. Albert Szent-Gyorgi �����������������������������������������������������������������������
From: Rune Allnor on 22 Mar 2010 11:18 On 22 Mar, 16:14, Jerry Avins <j...(a)ieee.org> wrote: > Rune Allnor wrote: > > ... > > > The spatial phase you talk about should be measured at 550 MHz, > > which is the signal that actually propagates down the physical > > channel. > > From what has been written, the signal is ordinary double-sideband AM. I didn't catch that SSB have been ruled out. > Make that 450 *and* 550 MHz, Agreed. Rune
From: glen herrmannsfeldt on 22 Mar 2010 13:58 Rune Allnor <allnor(a)tele.ntnu.no> wrote: > On 22 Mar, 00:48, glen herrmannsfeldt <g...(a)ugcs.caltech.edu> wrote: >>?After a signal goes through a dispersive >> medium (such as optical fiber), it then goes through a phase >> conjugation device. ?That reverses the effect such that passing >> through the same amount of fiber restores the original signal. >> That is, dispersive fiber+phase conjugation+dispersive fiber >> is, overall, not dispersive! > I remember reading some time in the mid / late '90s about a phase > conjugation tecnique used in a multipath scenario, in the context > of active sonars. Since phase conjugation in time domain amounts > to time reversal, these guys suggested to I understand phase conjugation for optical systems better, but... > 1) Emit a known waveform into the water > 2) Record the echo reflected off the target (which suffers from > reverberation, multipath and what not) > 3) Reverse the recorded signal and emit > 4) Record the reflection from the time-reversed recording The main thing this depends on is that conditions don't change (too much) between the two emission times. For time reversal, you can't start sending the time reversed signal until all of the first one is received. For optics, that time is related to the size of the phase conjugation device. > I never understood what the purpose of all this might have > been.In 'standard mode' there are all kinds of problems > detecting the reflection of interest inbetween all the > multipaths and distortions. If you already know these > factors, you also know the reference time around which > to flip the signal. I will guess that temperature gradients are part of the cause of dispersion. Presumably they change with time as currents move the water around. > If you are unable to untangle the recieved signal, you don't > know the key references, and effectively emit a random signal. > Even if the idea works, and you recieve something that is close > to the original pulse, you have no idea which part of the > emitted signal interacted with the target. Well, that problem is always there. > In the end, one have spent an awful lot of effort for no > gain at all. -- glen
From: WWalker on 22 Mar 2010 17:43 Hi Rune, What ever the the reason for this phenomina, given the known and excepted transfer function of a dipole source, It should be possible to transmit information faster than light by transmitting an AM signal in the nearfield and decoding the modulation. Simmulations clearly show that the envelope of an AM signal will arrive faster than light and undistorted in the nearfield. What is needed now is to find a way to decode the modulation within a fraction of (<1/10) a carrier cycle. >You need to be *extremely* cautious about what you are up to. >The stuff you are measuring is interference effects between >spherical waves, *not* the propagation of energy. It is very >easy to obtain infinite phase speeds in the case of plane waves: >A plane wave, in the ocean, that impinges perpendiculary to a >beach will exhibit an infinite phase speed along the beach. >The apparent wavelength is infinitely long, so the apparent >wave speed (phase velosity) is infinite. But the velocity >of information down the lenght of the beach is 0. > >Whatever it is you *think* you measure, similar effects >are in play. Check out the writings of Johan Leander in >the Journal of the Acoustical Society of America, in 1995 >or 1996. > >Rune >
From: Jerry Avins on 22 Mar 2010 17:45
WWalker wrote: > Hi Rune, > > Although the cross correlation method could perhaps be used to measure the > time delay of the modulation, this still does not help me. I want to > extract the modulation from the signal and show that it can be done in less > than a fraction (<1/10) of a carrier cycle. Dividing by the carrier does > this but the required SNR is too high to be practical. Transmitting > Q=A(t)Sin(Wct)and I=A(t)Cos(Wct)through the antennas and demodulating using > A(t)=Sqrt[I^2 + Q^2] also works. But I was hoping to find a method to > extract the modulation using only one signal, such as: A(t)Sin(Wct) > > Any ideas? You just don't pay attention to what's being said to you. I can't help you, so I'll stop trying. Jerry -- Discovery consists of seeing what everybody has seen, and thinking what nobody has thought. .. Albert Szent-Gyorgi ����������������������������������������������������������������������� |