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: Rune Allnor on 22 Mar 2010 18:07 On 22 Mar, 22:43, "WWalker" <william.walker(a)n_o_s_p_a_m.imtek.de> wrote: > 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. Wrong. Your simulations use fixed-parameter sinusoidals and have as such nothing to do with information, only steady states. Everything is known all the time; there is nothing new to be learned from observing the wave field. Hence, no information is transmitted. If you want to transmit *information*, you need to change something in the wavefield: The amplitude, the frequency or the phase. Something that is not known, that the reciever has to lock on to, detect and quantify. It is this *transient* change to an *unknown* state that carries the information down range between transmitter and reciever. I can guarantee that you will find that the transients propagate down range with a speed exactly equal to c. Rune
From: Randy Yates on 22 Mar 2010 18:14 Rune Allnor <allnor(a)tele.ntnu.no> writes: > [...] > I can guarantee that you will find that the transients > propagate down range with a speed exactly equal to c. <chuckle> -- Randy Yates % "Midnight, on the water... Digital Signal Labs % I saw... the ocean's daughter." mailto://yates(a)ieee.org % 'Can't Get It Out Of My Head' http://www.digitalsignallabs.com % *El Dorado*, Electric Light Orchestra
From: Tim Wescott on 22 Mar 2010 18:21 Rune Allnor wrote: > On 22 Mar, 22:43, "WWalker" <william.walker(a)n_o_s_p_a_m.imtek.de> > wrote: >> 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. > > Wrong. > > Your simulations use fixed-parameter sinusoidals and have > as such nothing to do with information, only steady states. > Everything is known all the time; there is nothing new to > be learned from observing the wave field. Hence, no > information is transmitted. > > If you want to transmit *information*, you need to change > something in the wavefield: The amplitude, the frequency > or the phase. Something that is not known, that the reciever > has to lock on to, detect and quantify. It is this *transient* > change to an *unknown* state that carries the information down > range between transmitter and reciever. > > I can guarantee that you will find that the transients > propagate down range with a speed exactly equal to c. Or perhaps slower in the near field -- certainly waves in a waveguide generally have a phase speed that's faster than c, but a group velocity that's slower. I wouldn't know if near field really is slower without doing the math, and I'd have to go back to school for a year or two to do that! Information encoded on entangled photons may or may not travel faster than light, but if they did so reliably and easily I would expect some commercial exploitation by now. -- Tim Wescott Control system and signal processing consulting www.wescottdesign.com
From: Jerry Avins on 22 Mar 2010 18:30 Rune Allnor wrote: > On 22 Mar, 22:43, "WWalker" <william.walker(a)n_o_s_p_a_m.imtek.de> > wrote: >> 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. > > Wrong. > > Your simulations use fixed-parameter sinusoidals and have > as such nothing to do with information, only steady states. > Everything is known all the time; there is nothing new to > be learned from observing the wave field. Hence, no > information is transmitted. > > If you want to transmit *information*, you need to change > something in the wavefield: The amplitude, the frequency > or the phase. Something that is not known, that the reciever > has to lock on to, detect and quantify. It is this *transient* > change to an *unknown* state that carries the information down > range between transmitter and reciever. > > I can guarantee that you will find that the transients > propagate down range with a speed exactly equal to c. Not necessarily that fast. Note that in waveguides, the product of phase ans group velocities is c^2. At cutoff, the group velocity drops to zero and the phase velocity becomes infinite. The energy travels transversely (cross the axis of the guide) giving infinite phase velocity like a wave straight onto a beach, so there is no energy traveling along the axis, making the group velocity zero. Jerry -- Discovery consists of seeing what everybody has seen, and thinking what nobody has thought. .. Albert Szent-Gyorgi �����������������������������������������������������������������������
From: WWalker on 22 Mar 2010 20:12
I dissagree. Simulation results show that if you add two signals with different frequencies and differnt amplitudes, the resultant signal changes in a random way as far as a detector is concerned. If the signal is modulated with a carrier and transmitted by a dipole antenna to another dipole antenna in the nearfield, the envelope of the received signal arrives undistorted, faster than light. This is because for a narrowband AM signal, the dispersion curve (phase and amplitude) is linear over the bandwidth of the signal. Provided the SNR is high enough, the random modulation information can then be decoded by dividing by the carrier. Comparing the transmitted modulation to the received modulation clearly shows that the modulation propagates undistorted, faster than light in the nearfield. But if a pulse is transmitted in the nearfield the pulse will distort because the dispersion curve (phase and amplitude) is not linear over the bandwidth of the signal, so group speed has no meaning in the nearfield. But in the farfield, the pulse will realign and propagate without distortion at the speed of light, so the pulse group speed only has meaning in the farfield. William >On 22 Mar, 22:43, "WWalker" <william.walker(a)n_o_s_p_a_m.imtek.de> >wrote: >> 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. > >Wrong. > >Your simulations use fixed-parameter sinusoidals and have >as such nothing to do with information, only steady states. >Everything is known all the time; there is nothing new to >be learned from observing the wave field. Hence, no >information is transmitted. > >If you want to transmit *information*, you need to change >something in the wavefield: The amplitude, the frequency >or the phase. Something that is not known, that the reciever >has to lock on to, detect and quantify. It is this *transient* >change to an *unknown* state that carries the information down >range between transmitter and reciever. > >I can guarantee that you will find that the transients >propagate down range with a speed exactly equal to c. > >Rune > |