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: Jerry Avins on 21 Mar 2010 16:53 WWalker wrote: > Hi Hardy, > > Unfortunately, the LPF will phase shift the modulation. So this technique > will not work for me. Do you know of any other way to extract the > modulation without using a filter? Why do you believe that? Think about what is being filtered. Jerry -- Discovery consists of seeing what everybody has seen, and thinking what nobody has thought. .. Albert Szent-Gyorgi �����������������������������������������������������������������������
From: WWalker on 21 Mar 2010 18:57 Hi Jerry, The low pass filter is used to filter out the higher harmonic terms generated by the mixer. But unfortunately, the filter phase shifts the wanted modulation. In my experiment I am transmitting a 50MHz Modulation signl with a 500MHz Carrier. If I use a simple 3rd order filter (1/(j(f/fc)+1)^3), with a 100MHz cutoff, the resultant modulation is phase shifted about 90 degrees. But, the effect I am trying to measure is a 3 degree change in modulation. William > >Use a PLL to get the carrier frequency and multiply and then low-pass >filter. Synchronous demodulation. >For supressed carrier you need to square the signal first then lock >onto 2f then divide by two and multiple - filter. >For low carrier to noise ratios you may need a different method. > >Hardy > >WWalker wrote: >> Hi Hardy, >> >> Unfortunately, the LPF will phase shift the modulation. So this technique >> will not work for me. Do you know of any other way to extract the >> modulation without using a filter? > >Why do you believe that? Think about what is being filtered. > >Jerry >-- >Discovery consists of seeing what everybody has seen, and thinking what >nobody has thought. .. Albert Szent-Gyorgi >����������������������������������������������������������������������� >
From: Randy Yates on 21 Mar 2010 19:06 "WWalker" <william.walker(a)n_o_s_p_a_m.imtek.de> writes: > Hi Hardy, > > Unfortunately, the LPF will phase shift the modulation. Not if you do it with a digital linear-phase filter. -- Randy Yates % "So now it's getting late, Digital Signal Labs % and those who hesitate mailto://yates(a)ieee.org % got no one..." http://www.digitalsignallabs.com % 'Waterfall', *Face The Music*, ELO
From: WWalker on 21 Mar 2010 19:09 I am a professional. Say something intelligent and perhaps we can talk about it. But being rude does not help. William > >It looks like you don't know what you doing. >Matlab is not a substitute for knowledge. > From here, you can either seek for professional help or study an ABC=20 >book on DSP from cover to cover. > >VLV
From: Vladimir Vassilevsky on 21 Mar 2010 19:19
I am *the* professional. I need to know the problem statement. I.e. what is the input, what should be the output, what is the accuracy and what hardware is available. Your problem will probably take 3-4 hours of work. The cost is going to be $1000. Is this OK ? Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com WWalker wrote: > I am a professional. Say something intelligent and perhaps we can talk > about it. But being rude does not help. > > William > > >>It looks like you don't know what you doing. >>Matlab is not a substitute for knowledge. >>From here, you can either seek for professional help or study an ABC=20 >>book on DSP from cover to cover. >> >>VLV > > > |