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| Computers Forum Index » Computer - DSP » measured bandwidth... |
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| fisico32... |
 Posted: Wed Oct 21, 2009 12:04 am |
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Guest
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hello Forum,
a real signal has a bandwidth DELTA_f of positive frequencies. The
bandwidth is the range of frequencies from DC=f=0 to f_max. Only positive
frequencies make sense physically. Negativ freq. are just a math artifact.
Mathematically,the frequency bandwidth is 2*DELTA_f, since the FT done
with complex exponentials has a redundant frequency content in the negative
frequency part of the spectrum, from -f_max<f<0
Do actual spectrum analyzers show DELTA_f or 2*DELTA_f? Do the inner
workings of a system processing an input signal need to take into account a
BW= DELTA_f or 2*DELTA_f?
I would say 2*DELTA_f, since any processing system operates based on
mathematical formulas that we program in the system....
thanks
fisico32 |
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| Jerry Avins... |
| Posted: Wed Oct 21, 2009 12:07 am |
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Guest
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fisico32 wrote:
Quote: hello Forum,
a real signal has a bandwidth DELTA_f of positive frequencies. The
bandwidth is the range of frequencies from DC=f=0 to f_max. Only positive
frequencies make sense physically. Negativ freq. are just a math artifact.
Mathematically,the frequency bandwidth is 2*DELTA_f, since the FT done
with complex exponentials has a redundant frequency content in the negative
frequency part of the spectrum, from -f_max<f<0
Do actual spectrum analyzers show DELTA_f or 2*DELTA_f? Do the inner
workings of a system processing an input signal need to take into account a
BW= DELTA_f or 2*DELTA_f?
I would say 2*DELTA_f, since any processing system operates based on
mathematical formulas that we program in the system....
All the onds I ever used showed the one-sided spactrum.
Jerry
--
Engineering is the art of making what you want from things you can get.
ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ |
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| Eric Jacobsen... |
| Posted: Wed Oct 21, 2009 1:51 am |
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On 10/20/2009 1:07 PM, Jerry Avins wrote:
Quote: fisico32 wrote:
hello Forum,
a real signal has a bandwidth DELTA_f of positive frequencies. The
bandwidth is the range of frequencies from DC=f=0 to f_max. Only positive
frequencies make sense physically. Negativ freq. are just a math
artifact.
Mathematically,the frequency bandwidth is 2*DELTA_f, since the FT done
with complex exponentials has a redundant frequency content in the
negative
frequency part of the spectrum, from -f_max<f<0
Do actual spectrum analyzers show DELTA_f or 2*DELTA_f? Do the inner
workings of a system processing an input signal need to take into
account a
BW= DELTA_f or 2*DELTA_f?
I would say 2*DELTA_f, since any processing system operates based on
mathematical formulas that we program in the system....
All the onds I ever used showed the one-sided spactrum.
Jerry
Most Spectrum Analyzers that I've used will show two-sided spectra, as
DC always shows up as a big spike, so it's easy to pick out. Often the
ability to see very far into negative frequencies isn't great as it
doesn't need to be. The Anritsu on my bench will do this with no problem.
Since the measurement is real-valued there's symmetry around 0 Hz, as
expected.
--
Eric Jacobsen
Minister of Algorithms
Abineau Communications
http://www.abineau.com |
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