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Hilbert Transform Problem

Started by Unknown April 30, 2009
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
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 > > aitezaz
Ok - Hilbert transformers are delicate. Did you handle it properly? Sometimes the windings on the secondary can come off. Hardy
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
On Apr 30, 12:06&#2013266080;pm, John <sampson...@gmail.com> wrote:
> On Apr 30, 10:44&#2013266080;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 ? aitezaz
On May 1, 9:37&#2013266080;am, aitezaz....@gmail.com wrote:
> On Apr 30, 12:06&#2013266080;pm, John <sampson...@gmail.com> wrote: > > > > > On Apr 30, 10:44&#2013266080;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 ? > > aitezaz
It should be close. John