hi! i want to demodulate AM signal digitally... i want to use a digital filter to separate the carrier and the information signal. i've searched a lot...and i haven't found the answer. can anyone help?please... thx... -chris(c1910)- _____________________________________ Do you know a company who employs DSP engineers? Is it already listed at http://dsprelated.com/employers.php ?
AM demodulation using DSP
Started by ●June 3, 2007
Reply by ●June 3, 20072007-06-03
c1910 wrote:> hi! > i want to demodulate AM signal digitally...And I want $100.> i want to use a digital filter to separate the carrier and the information > signal.Sure. As for me, the US$ is preferrable.> i've searched a lot...Me too! Where can I find $100?> and i haven't found the answer.Why? You have found me!> can anyone help?please...Certainly. I help you, you help me.> thx...Your "Thanks" means so much to me. There is no need to thank; $100 will be just all right.> -chris(c1910)- >VLV
Reply by ●June 3, 20072007-06-03
c1910 wrote:> hi! > i want to demodulate AM signal digitally... > i want to use a digital filter to separate the carrier and the information > signal. i've searched a lot...and i haven't found the answer. > can anyone help?please... > thx...The last time you asked this question, you were told that you can't demodulate with a filter. The laws of physics haven't changed in th last week or so. Jerry -- Engineering is the art of making what you want from things you can get. ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
Reply by ●June 3, 20072007-06-03
Jerry Avins <jya@ieee.org> writes:> c1910 wrote: >> hi! >> i want to demodulate AM signal digitally... >> i want to use a digital filter to separate the carrier and the information >> signal. i've searched a lot...and i haven't found the answer. >> can anyone help?please... >> thx... > > The last time you asked this question, you were told that you can't > demodulate with a filter. The laws of physics haven't changed in th > last week or so.Well, actually you could with a filter and decimator, if your sample rate is just right... -- % Randy Yates % "She has an IQ of 1001, she has a jumpsuit %% Fuquay-Varina, NC % on, and she's also a telephone." %%% 919-577-9882 % %%%% <yates@ieee.org> % 'Yours Truly, 2095', *Time*, ELO http://home.earthlink.net/~yatescr
Reply by ●June 3, 20072007-06-03
Randy Yates wrote:> Jerry Avins <jya@ieee.org> writes: > >> c1910 wrote: >>> hi! >>> i want to demodulate AM signal digitally... >>> i want to use a digital filter to separate the carrier and the information >>> signal. i've searched a lot...and i haven't found the answer. >>> can anyone help?please... >>> thx... >> The last time you asked this question, you were told that you can't >> demodulate with a filter. The laws of physics haven't changed in th >> last week or so. > > Well, actually you could with a filter and decimator, if your sample > rate is just right...That's called "synchronous demodulation", no? You don't even need an explicit filter if you don't care about the inaudible stuff. A customer's hi-fi system distorted and overheated, but only when he listened to AM. It turned out that his 25-watt power amplifier was pumping 22 watts (equivalent voltage) at 456 KHz into the loudspeaker. (The tweeter got warm too.) I fixed the post-detection filter and all was well. So there may be reason to care about the inaudible stuff. Jerry -- Engineering is the art of making what you want from things you can get. ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
Reply by ●June 3, 20072007-06-03
Jerry Avins wrote:> c1910 wrote: >> hi! >> i want to demodulate AM signal digitally... >> i want to use a digital filter to separate the carrier and the >> information >> signal. i've searched a lot...and i haven't found the answer. >> can anyone help?please... >> thx... > > The last time you asked this question, you were told that you can't > demodulate with a filter. The laws of physics haven't changed in th last > week or so. > > JerryWell, if you extend your definition of "filter" to include time-varying and nonlinear filters... Hey, do you include "don't ask the same question twice" in your procedural FAQ? -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Posting from Google? See http://cfaj.freeshell.org/google/ Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" gives you just what it says. See details at http://www.wescottdesign.com/actfes/actfes.html
Reply by ●June 3, 20072007-06-03
Jerry Avins <jya@ieee.org> writes:> Randy Yates wrote: >> Jerry Avins <jya@ieee.org> writes: >> >>> c1910 wrote: >>>> hi! >>>> i want to demodulate AM signal digitally... >>>> i want to use a digital filter to separate the carrier and the information >>>> signal. i've searched a lot...and i haven't found the answer. >>>> can anyone help?please... >>>> thx... >>> The last time you asked this question, you were told that you can't >>> demodulate with a filter. The laws of physics haven't changed in th >>> last week or so. >> Well, actually you could with a filter and decimator, if your sample >> rate is just right... > > That's called "synchronous demodulation", no?I don't know, Jerry. I've heard of that term but haven't seen it defined. Rick calls this "bandpass sampling" in [lyonsnew].> You don't even need an explicit filter if you don't care about the > inaudible stuff.Well it would be audible in this case due to aliasing.> A customer's hi-fi system distorted and overheated, but only when he > listened to AM. It turned out that his 25-watt power amplifier was > pumping 22 watts (equivalent voltage) at 456 KHz into the > loudspeaker. (The tweeter got warm too.) I fixed the post-detection > filter and all was well. So there may be reason to care about the > inaudible stuff.Who woulda' thunk the power amp had a usable response out to 456 kHz??? --Randy @BOOK{lyonsnew, title = "{Understanding Digital Signal Processing}", edition = "Second", author = "{Richard~G.~Lyons}", publisher = "Prentice Hall", year = "2004"} -- % Randy Yates % "I met someone who looks alot like you, %% Fuquay-Varina, NC % she does the things you do, %%% 919-577-9882 % but she is an IBM." %%%% <yates@ieee.org> % 'Yours Truly, 2095', *Time*, ELO http://home.earthlink.net/~yatescr
Reply by ●June 3, 20072007-06-03
Randy Yates wrote:> Jerry Avins <jya@ieee.org> writes: > >> Randy Yates wrote: >>> Jerry Avins <jya@ieee.org> writes: >>> >>>> c1910 wrote: >>>>> hi! >>>>> i want to demodulate AM signal digitally... >>>>> i want to use a digital filter to separate the carrier and the information >>>>> signal. i've searched a lot...and i haven't found the answer. >>>>> can anyone help?please... >>>>> thx... >>>> The last time you asked this question, you were told that you can't >>>> demodulate with a filter. The laws of physics haven't changed in th >>>> last week or so. >>> Well, actually you could with a filter and decimator, if your sample >>> rate is just right... >> That's called "synchronous demodulation", no? > > I don't know, Jerry. I've heard of that term but haven't seen it defined. > Rick calls this "bandpass sampling" in [lyonsnew].If your "right sampling frequency" is phase locked to the carrier, that amounts to synchronous demodulation.>> You don't even need an explicit filter if you don't care about the >> inaudible stuff. > > Well it would be audible in this case due to aliasing.There would be no aliasing in the demodulated signal. Where would it come from?>> A customer's hi-fi system distorted and overheated, but only when he >> listened to AM. It turned out that his 25-watt power amplifier was >> pumping 22 watts (equivalent voltage) at 456 KHz into the >> loudspeaker. (The tweeter got warm too.) I fixed the post-detection >> filter and all was well. So there may be reason to care about the >> inaudible stuff. > > Who woulda' thunk the power amp had a usable response out to 456 kHz???I thought it was strange too, so I measured the response. It was about 30 dB down. There was a *lot* of IF coming out of the tuner. There's more to the story. The customer was an audio nut who was convinced that the tuner suffered from diagonal clipping, and maybe it was. See http://tinyurl.com/3a5d5u He replaced the filter cap with a smaller one that happened to be defective: open. To cater to his paranoia, I replaced the half-wave detector with a full wave, doubling the frequency that needed to be filtered to 912 KHz, thereby allowing a smaller filter cap and riding even further down the power amplifier's rolloff. Jerry -- Engineering is the art of making what you want from things you can get. ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
Reply by ●June 3, 20072007-06-03
> > Who woulda' thunk the power amp had a usable response out to 456 kHz??? >Hello Randy, I recall looking at designs for audio amps that used current feed back as opposed to the more common voltage feedback. The current feedback amps were flat to several MHz. And to get this kind of frequency response required nothing special in terms of components. Just the change in topology made the difference. There are quite a few appnotes out there on such amplifier designs. Clay
Reply by ●June 3, 20072007-06-03
Jerry Avins wrote:>>> A customer's hi-fi system distorted and overheated, but only when he >>> listened to AM. It turned out that his 25-watt power amplifier was >>> pumping 22 watts (equivalent voltage) at 456 KHz into the >>> loudspeaker. (The tweeter got warm too.)Oh, come on, Jerry. That can't be due to inductance of the tweeter. The typical value is about 0.5uH. I fixed the post-detection>>> filter and all was well. So there may be reason to care about the >>> inaudible stuff. >> >> Who woulda' thunk the power amp had a usable response out to 456 kHz??? > > > I thought it was strange too, so I measured the response. It was about > 30 dB down.???? The small signal bandwidth of the decent audio amplifier should be well above 1MHz. If this 30dB fall is due to the slew rate limitation, then the full power bandwidth is only about 70kHz. A fair result, not HiFi by any means.> There was a *lot* of IF coming out of the tuner. There's > more to the story. The customer was an audio nut who was convinced that > the tuner suffered from diagonal clipping, and maybe it was. See > http://tinyurl.com/3a5d5u He replaced the filter cap with a smaller one > that happened to be defective: open. To cater to his paranoia, I > replaced the half-wave detector with a full wave, doubling the frequency > that needed to be filtered to 912 KHz, thereby allowing a smaller filter > cap and riding even further down the power amplifier's rolloff. > > JerryVladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com
