Hi,
I need some hints suggestion on calculating the spectrum of the a
pulse width modulated signal. I have a 100kHz pulse signal. The width
of the pulse is modulated by another low frequency sine wave (100Hz)
so that the pulse width of 100kHz signal varies from 10% to 90%. I
want to compute the magnitude of the average spectrum. The average
being taken over the time period of 10ms(i.e. period of 100Hz).
Kindly
suggest how to proceed with it. Any reference would be great start
for
me.
Thanks.
Kristo

On Mon, 20 Aug 2007 03:33:10 -0700, kristo <krishmaniac@hotmail.com>
wrote:

>Hi,
>I need some hints suggestion on calculating the spectrum of the a
>pulse width modulated signal. I have a 100kHz pulse signal. The width
>of the pulse is modulated by another low frequency sine wave (100Hz)
>so that the pulse width of 100kHz signal varies from 10% to 90%. I
>want to compute the magnitude of the average spectrum. The average
>being taken over the time period of 10ms(i.e. period of 100Hz).
>Kindly
>suggest how to proceed with it. Any reference would be great start
>for
>me.
>Thanks.
>Kristo

Lots of engineering handbooks have tables of spectra of various
waveforms. The classic "Reference Data for Radio Engineers" lists this
exact waveform. They even have a version for the case of finite rise
and fall times.

John

On Mon, 20 Aug 2007 03:33:10 -0700, kristo <krishmaniac@hotmail.com>
wrote:

>Hi,
>I need some hints suggestion on calculating the spectrum of the a
>pulse width modulated signal. I have a 100kHz pulse signal. The width
>of the pulse is modulated by another low frequency sine wave (100Hz)
>so that the pulse width of 100kHz signal varies from 10% to 90%. I
>want to compute the magnitude of the average spectrum. The average
>being taken over the time period of 10ms(i.e. period of 100Hz).
>Kindly
>suggest how to proceed with it. Any reference would be great start
>for
>me.
>Thanks.
>Kristo

Can't help on the calculations, but if you want to visualize it you
can download Daqarta and use the built-in signal generator and
spectrum/waveform/spectrogram analyzers.

Daqarta works with your sound card at audio frequencies, so you'd have
to scale the pulse and modulating frequencies appropriately.
(You may or may not want to listen to the results.)

The built-in PWM controls can use simple sine modulators, or
the output of a separate generator "stream" (streams 4 per channel).
The modulating stream can be any waveform, including any
arbitrary WAV file.

Note that there is no need to purchase Daqarta for this.
Even after the trial period expires, all the above features
remain available... you just can't view signals from the sound
card inputs.

Best regards,


Bob Masta

D A Q A R T A
Data AcQuisition And Real-Time Analysis
http://www.daqarta.com
Scope, Spectrum, Spectrogram, Signal Generator
Science with your sound card!