Reply by Eric Jacobsen●September 19, 20092009-09-19
On 9/18/2009 4:18 PM, JAlbertoDJ wrote:
>> JAlbertoDJ wrote:
>>>> Hi, all
>>>>
>>>> I want to demodulate an IF real signal and it seems that there are
> some
>>>> different methods on it. I can employ hilbert transform to construct
> the
>>>> analytic signal and downconvert it to baseband. Otherwise, I can get
> the
>>>> signal multiplied by a sine and a cosine which oscillate at IF
> carrier
>>>> frequency and then lowpass-filter unwanted parts. These two methods
> now
>>>> also deal with complex numbers.
>>>>
>>>> What is the difference between these two methods? I can't tell which
> is
>>>> superior.
>> ...
>>
>>> If you multiply by a sine and a cosine which oscillate at IF carrier
>>> frequency you loss phase information.
>> Did Horus, the god of mathematics, tell you that? According to the math
>> I know, phase is preserved.
>>
>> ...
>>
>> Jerry
>> --
>> Engineering is the art of making what you want from things you can get.
>> �����������������������������������������������������������������������
>>
>
> I have wrote that because multiplying by a sine and a cosine i cannot do
> run an Automatic Frecuency Control for my modem using atan(Im/Re) in the
> FFT output.
>
> Otherwise, with Hilbert transform instead of multiplying, AFC run
> perfectly. why? i dont know, and i would like something explain to me.
>
> In the example of PSK demodulation you dont have any problem with phase.
> But....try to apply an AFC to your PSK demodulator and then tell me if
> converge.
Yes, the AFC will converge, as will a loop locked onto the carrier phase.
--
Eric Jacobsen
Minister of Algorithms
Abineau Communications
http://www.abineau.com
Reply by JAlbertoDJ●September 18, 20092009-09-18
>JAlbertoDJ wrote:
>>> Hi, all
>>>
>>> I want to demodulate an IF real signal and it seems that there are
some
>>> different methods on it. I can employ hilbert transform to construct
the
>>> analytic signal and downconvert it to baseband. Otherwise, I can get
the
>>> signal multiplied by a sine and a cosine which oscillate at IF
carrier
>>> frequency and then lowpass-filter unwanted parts. These two methods
now
>>> also deal with complex numbers.
>>>
>>> What is the difference between these two methods? I can't tell which
is
>>> superior.
>
> ...
>
>> If you multiply by a sine and a cosine which oscillate at IF carrier
>> frequency you loss phase information.
>
>Did Horus, the god of mathematics, tell you that? According to the math
>I know, phase is preserved.
>
> ...
>
>Jerry
>--
>Engineering is the art of making what you want from things you can get.
>�����������������������������������������������������������������������
>
I have wrote that because multiplying by a sine and a cosine i cannot do
run an Automatic Frecuency Control for my modem using atan(Im/Re) in the
FFT output.
Otherwise, with Hilbert transform instead of multiplying, AFC run
perfectly. why? i dont know, and i would like something explain to me.
In the example of PSK demodulation you dont have any problem with phase.
But....try to apply an AFC to your PSK demodulator and then tell me if
converge.
Reply by Jerry Avins●September 18, 20092009-09-18
JAlbertoDJ wrote:
>> Hi, all
>>
>> I want to demodulate an IF real signal and it seems that there are some
>> different methods on it. I can employ hilbert transform to construct the
>> analytic signal and downconvert it to baseband. Otherwise, I can get the
>> signal multiplied by a sine and a cosine which oscillate at IF carrier
>> frequency and then lowpass-filter unwanted parts. These two methods now
>> also deal with complex numbers.
>>
>> What is the difference between these two methods? I can't tell which is
>> superior.
...
> If you multiply by a sine and a cosine which oscillate at IF carrier
> frequency you loss phase information.
Did Horus, the god of mathematics, tell you that? According to the math
I know, phase is preserved.
...
Jerry
--
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������
Reply by Eric Jacobsen●September 18, 20092009-09-18
On 9/17/2009 5:07 PM, JAlbertoDJ wrote:
>> Hi, all
>>
>> I want to demodulate an IF real signal and it seems that there are some
>> different methods on it. I can employ hilbert transform to construct the
>> analytic signal and downconvert it to baseband. Otherwise, I can get the
>> signal multiplied by a sine and a cosine which oscillate at IF carrier
>> frequency and then lowpass-filter unwanted parts. These two methods now
>> also deal with complex numbers.
>>
>> What is the difference between these two methods? I can't tell which is
>> superior.
>>
>> Thanks for answering.
>>
>>
>
> If you multiply by a sine and a cosine which oscillate at IF carrier
> frequency you loss phase information. If you dont need thats information
> you can use that method. Otherwise, you need hilbert transform.
How so? PSK modems, where the information is in the phase, use
quadrature mixing for up and downconversion routinely.
--
Eric Jacobsen
Minister of Algorithms
Abineau Communications
http://www.abineau.com
Reply by alomar●September 17, 20092009-09-17
>>Hi, all
>>
>>I want to demodulate an IF real signal and it seems that there are some
>>different methods on it. I can employ hilbert transform to construct
the
>>analytic signal and downconvert it to baseband. Otherwise, I can get
the
>>signal multiplied by a sine and a cosine which oscillate at IF carrier
>>frequency and then lowpass-filter unwanted parts. These two methods now
>>also deal with complex numbers.
>>
>>What is the difference between these two methods? I can't tell which is
>>superior.
>>
>>Thanks for answering.
>>
>>
>
>If you multiply by a sine and a cosine which oscillate at IF carrier
>frequency you loss phase information. If you dont need thats information
>you can use that method. Otherwise, you need hilbert transform.
>
thank you all, your advice really help me a lot
Reply by JAlbertoDJ●September 17, 20092009-09-17
>Hi, all
>
>I want to demodulate an IF real signal and it seems that there are some
>different methods on it. I can employ hilbert transform to construct the
>analytic signal and downconvert it to baseband. Otherwise, I can get the
>signal multiplied by a sine and a cosine which oscillate at IF carrier
>frequency and then lowpass-filter unwanted parts. These two methods now
>also deal with complex numbers.
>
>What is the difference between these two methods? I can't tell which is
>superior.
>
>Thanks for answering.
>
>
If you multiply by a sine and a cosine which oscillate at IF carrier
frequency you loss phase information. If you dont need thats information
you can use that method. Otherwise, you need hilbert transform.
Reply by Clay●September 17, 20092009-09-17
On Sep 17, 2:52�am, "alomar" <alomar.w...@gmail.com> wrote:
> Hi, all
>
> I want to demodulate an IF real signal and it seems that there are some
> different methods on it. I can employ hilbert transform to construct the
> analytic signal and downconvert it to baseband. Otherwise, I can get the
> signal multiplied by a sine and a cosine which oscillate at IF carrier
> frequency and then lowpass-filter unwanted parts. These two methods now
> also deal with complex numbers.
>
> What is the difference between these two methods? I can't tell which is
> superior.
>
> Thanks for answering.
Reply by Vladimir Vassilevsky●September 17, 20092009-09-17
alomar wrote:
> Hi, all
>
> I want to demodulate an IF real signal and it seems that there are some
> different methods on it. I can employ hilbert transform to construct the
> analytic signal and downconvert it to baseband. Otherwise, I can get the
> signal multiplied by a sine and a cosine which oscillate at IF carrier
> frequency and then lowpass-filter unwanted parts. These two methods now
> also deal with complex numbers.
>
> What is the difference between these two methods?
As long as you can separate the mirror images, both methods are equvalent.
> I can't tell which is superior.
You have to use Hilbert transform if the image spectrum overlaps with
the downconverted spectrum.
Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com
Reply by Vladimir Vassilevsky●September 17, 20092009-09-17
alomar wrote:
> Hi, all
>
> I want to demodulate an IF real signal and it seems that there are some
> different methods on it. I can employ hilbert transform to construct the
> analytic signal and downconvert it to baseband. Otherwise, I can get the
> signal multiplied by a sine and a cosine which oscillate at IF carrier
> frequency and then lowpass-filter unwanted parts. These two methods now
> also deal with complex numbers.
>
> What is the difference between these two methods?
As long as you can separate the mirror images, both methods are equvalent.
> I can't tell which is superior.
You have to use Hilbert transform if the image spectrum overlaps with
the downconverted spectrum.
Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com
Reply by alomar●September 17, 20092009-09-17
Hi, all
I want to demodulate an IF real signal and it seems that there are some
different methods on it. I can employ hilbert transform to construct the
analytic signal and downconvert it to baseband. Otherwise, I can get the
signal multiplied by a sine and a cosine which oscillate at IF carrier
frequency and then lowpass-filter unwanted parts. These two methods now
also deal with complex numbers.
What is the difference between these two methods? I can't tell which is
superior.
Thanks for answering.