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From: | Marcus Müller |
Subject: | Re: [Discuss-gnuradio] Simple GMSK encoder and decoder with very large bandwidth |
Date: | Thu, 20 Apr 2017 20:11:15 +0200 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.2.0 |
As said, the bandwidth displayed is really just labeled that way because you configured the FFT sink to use the arbitrary number 32000 as full frequency range. If you instead put in 1000 in the same place, your signal will instantly look only 1/32 as wide :) So, the takeaway here is: that GMSK signal takes up about 70% of the Nyquist bandwidth (i.e. your sampling rate). There's nothing wrong with that! Point is: GNU Radio just pushes around sequences of numbers. Nothing more. They don't have any inherent frequency info. Something that happens with a period two samples simply has twice the frequency that happens to have a period of 4 samples! So, what the FFT sink does is simply take things that take 4 samples and display them at one fourth of the x-range. The labels below that axis are just scaled to fit your display "as if" you were converting that signal to analog at the rate you set as bandwidth in the display. *the scaling of the x-axis says zero about what you do with the signal*, it's still just a sequence of numbers. So, your actual GMSK bandwidth depends on what sampling rate you choose – and what BT and samples per symbol setting you use :) Best regards, Marcus On 04/20/2017 08:01 PM, Fred Castello
wrote:
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