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 8 Mar 2010 05:38 >robert bristow-johnson wrote: >I would like to understand what dividing by the carrier would do. I >almost get it, but the carrier is zero twice a cycle. > >Jerry ----------------------------------- Given an AM signal: Sig = A Cos[wm t]*Cos[wc t]. Then the modulation envelope can be obtained by simple dividing by the carrier: Sig/Cos[wc t] = A Cos[wm t]. But the problem is that when the carrier goes to zero the result goes to infinity. One way arround the problem is to add an offset to the carrier so that the carrier never goes to zero, but this completely changes the signal. William
From: WWalker on 8 Mar 2010 05:57 >On Mar 7, 10:37=A0pm, Jerry Avins <j...(a)ieee.org> wrote: >one thing i would like to figure out is what the OP means by "without >phase shift". if he/she means no delay in the detection alg, then >Hilbert is out of the picture completely. > >r b-j ------------------------ I simply want a very good match when I overlay the AM Signal with the calculated envelope. In order for this to work the calculated envelope can not be phase shifted. William
From: ok1iak on 8 Mar 2010 06:55 > Regarding the Hilbert Transform method, I squared the signal and added it > to the square of the Hilbert transform of the signal. Then I took the > square root of the result. This technique extracts the envelope without a > phase shift, but it does introduce problematic oscillations near the > beginning and end of the signal. I do not want to use a filter to get rid > of the oscillations because it will add a phase shift to the envelope. Both I and Q components shall be fed through the same low pass filter that your Hilbert filter was designed from. From your description it seems like your I component is fed directly without low pass filtering. Maybe the oscillation is an effect the impulse response of your low pass filter? Vojtech
From: Jerry Avins on 8 Mar 2010 09:31 WWalker wrote: >> On Mar 7, 10:37=A0pm, Jerry Avins <j...(a)ieee.org> wrote: > >> one thing i would like to figure out is what the OP means by "without >> phase shift". if he/she means no delay in the detection alg, then >> Hilbert is out of the picture completely. >> >> r b-j > ------------------------ > I simply want a very good match when I overlay the AM Signal with the > calculated envelope. In order for this to work the calculated envelope can > not be phase shifted. Of course it can. Delay the signal an equal amount. Jerry -- It matters little to a goat whether it be dedicated to God or consigned to Azazel. The critical turning was having been chosen to participate. �����������������������������������������������������������������������
From: Vladimir Vassilevsky on 8 Mar 2010 09:53
WWalker wrote: >>robert bristow-johnson wrote: > > >>I would like to understand what dividing by the carrier would do. I >>almost get it, but the carrier is zero twice a cycle. >> >>Jerry > > ----------------------------------- > > Given an AM signal: Sig = A Cos[wm t]*Cos[wc t]. Then the modulation > envelope can be obtained by simple dividing by the carrier: > Sig/Cos[wc t] = A Cos[wm t]. JFYI: AM = A [1 + M cos (wm t)] cos (wc t) > But the problem is that when the carrier goes > to zero the result goes to infinity. One way arround the problem is to add > an offset to the carrier so that the carrier never goes to zero, but this > completely changes the signal. You do weird things in the weird ways. VLV |