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[Discuss-gnuradio] Freq in real world vs. Freq in the SW

From: Milo Wong
Subject: [Discuss-gnuradio] Freq in real world vs. Freq in the SW
Date: Mon, 21 Sep 2009 16:16:02 -0700
User-agent: Thunderbird (X11/20090817)

Hi folks,

I wrote a amplitude modulation block and here's an interesting problem:

It seemed that the Freq showed on the plot of post modulation FFT is always (1/80) of the freq I set in the SW. For example, If I set the sub-carrier freq to 2MHz, and use a message signal (constant 1.0)to modulate that, I can only get a 50KHz sub-carrier showed on FFT plot. I've attached my plots(both in freq and time domain).

Below are the test results:
freq. in post-mod FFT       freq. set in SW
    12.5k                             1M
     25k                               2M
     50k                               4M

Is there anyone who has some ideas or comments? Thank you!


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