Dear All, I have a question regarding hilbert transformer. If i take the bandpass signal and sample it it would be real. Now when i multiply it with a complex exponential to downconvert it I get a complex baseband signal. On the other hand, if i take the bandpass signal, pass it through a hilbert transformer and get a complex signal, and then downconvert using complex multiplication i get different baseband data. Why is it so as in both cases I am multiplying with a complex exponential. In summary, what is the difference between these two methods of downconversion. i). multiplying real data with complex exponential -> complex output ii). multiplying complex passband data with complex exponential -> complex output aitezaz
Hilbert Transform Problem
Started by ●April 30, 2009
Reply by ●April 30, 20092009-04-30
On May 1, 2:44�am, aitezaz....@gmail.com wrote:> Dear All, > I have a question regarding hilbert transformer. If i take the > bandpass signal and sample it it would be real. Now when i multiply it > with a complex exponential to downconvert it I get a complex baseband > signal. On the other hand, if i take the bandpass signal, pass it > through a hilbert transformer and get a complex signal, and then > downconvert using complex multiplication i get different baseband > data. Why is it so as in both cases I am multiplying with a complex > exponential. In summary, what is the difference between these two > methods of downconversion. > i). multiplying real data with complex exponential -> complex output > ii). multiplying complex passband data with complex exponential -> > complex output > > aitezazOk - Hilbert transformers are delicate. Did you handle it properly? Sometimes the windings on the secondary can come off. Hardy
Reply by ●April 30, 20092009-04-30
On Apr 30, 10:44�am, aitezaz....@gmail.com wrote:> Dear All, > I have a question regarding hilbert transformer. If i take the > bandpass signal and sample it it would be real. Now when i multiply it > with a complex exponential to downconvert it I get a complex baseband > signal. On the other hand, if i take the bandpass signal, pass it > through a hilbert transformer and get a complex signal, and then > downconvert using complex multiplication i get different baseband > data. Why is it so as in both cases I am multiplying with a complex > exponential. In summary, what is the difference between these two > methods of downconversion. > i). multiplying real data with complex exponential -> complex output > ii). multiplying complex passband data with complex exponential -> > complex output > > aitezazCase i) will contain baseband plus an image. Case ii) will not. John
Reply by ●May 1, 20092009-05-01
On Apr 30, 12:06�pm, John <sampson...@gmail.com> wrote:> On Apr 30, 10:44�am, aitezaz....@gmail.com wrote: > > > Dear All, > > I have a question regarding hilbert transformer. If i take the > > bandpass signal and sample it it would be real. Now when i multiply it > > with a complex exponential to downconvert it I get a complex baseband > > signal. On the other hand, if i take the bandpass signal, pass it > > through a hilbert transformer and get a complex signal, and then > > downconvert using complex multiplication i get different baseband > > data. Why is it so as in both cases I am multiplying with a complex > > exponential. In summary, what is the difference between these two > > methods of downconversion. > > i). multiplying real data with complex exponential -> complex output > > ii). multiplying complex passband data with complex exponential -> > > complex output > > > aitezaz > > Case i) will contain baseband plus an image. Case ii) will not. > > JohnThanks john! i got it right.... and if i want to make these two cases the same, should i LPF filter the I and Q channels in case i). And i will get the same output ? aitezaz
Reply by ●May 1, 20092009-05-01
On May 1, 9:37�am, aitezaz....@gmail.com wrote:> On Apr 30, 12:06�pm, John <sampson...@gmail.com> wrote: > > > > > On Apr 30, 10:44�am, aitezaz....@gmail.com wrote: > > > > Dear All, > > > I have a question regarding hilbert transformer. If i take the > > > bandpass signal and sample it it would be real. Now when i multiply it > > > with a complex exponential to downconvert it I get a complex baseband > > > signal. On the other hand, if i take the bandpass signal, pass it > > > through a hilbert transformer and get a complex signal, and then > > > downconvert using complex multiplication i get different baseband > > > data. Why is it so as in both cases I am multiplying with a complex > > > exponential. In summary, what is the difference between these two > > > methods of downconversion. > > > i). multiplying real data with complex exponential -> complex output > > > ii). multiplying complex passband data with complex exponential -> > > > complex output > > > > aitezaz > > > Case i) will contain baseband plus an image. Case ii) will not. > > > John > > Thanks john! > i got it right.... and if i want to make these two cases the same, > should i LPF filter the I and Q channels in case i). And i will get > the same output ? > > aitezazIt should be close. John