Tutorial 2.4.5 The Singing Sine Wave

Hi,

I have two questions to the above mentioned Tutorial chapter, since I
realized two differences, even though I think I set it up the same.

a) To get an acceptable view in the Waterfall graph I had to adjust the
frequency to a fourth of the suggested value in the tutorial picture.
Please compare in my attachment Flowgraph_2-4-5.png, where the value is
marked with a red arrow. Why could that be?

b) How could it be managed to set the X-axis of the Waterfall graph from
-50 to 50 in the picture of the tutorial? In the documentation is stated
that this is related to the bandwidth value of the GUI Waterfall item.
So I could only change this by setting the bandwidth to 100k. But than
the maximum frequency is shown as 40kHz instead of 20kHz and the
triangle pattern stays the same. This does not seem correct, as the
frequency reading would be wrong. Please look at Waterfall_2-4-5.png.
Again marked with red arrows.

Refers to:
http://gnuradio.org/redmine/projects/gnuradio/wiki/Guided_Tutorial_GRC
– Scroll to 2.4.5

Best regards
Mike

On 08/14/2015 04:52 PM, Michael Thelen DK4MT wrote:

b) How could it be managed to set the X-axis of the Waterfall graph from
– Scroll to 2.4.5

Best regards
Mike


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The “bandwidth” setting on the waterfall is just to allow it compute the
X-axis legend along the bottom, which in your attached pics shows -24kHz
to +24kHz,
although the last actual numeric marker in each direction is
+/-20kHz.

Again, if you set the bandwidth to 100kHz in the waterfall, that will
dutifully calculate the markers to show +/-50kHz. But setting the
“bandwidth” in the
waterfall does nothing about the actual delivered sample rate. It’s
just a hint to the plotter about the bandwidth of your signal. Nearly
the entirety
of Gnu Radio doesn’t really “know” anything about sample rates–they
are an artifice that only becomes “real” at the edges with actual
hardware, and
also as a convenience when calculating filter parameters.

Am 15.08.2015 um 01:55 schrieb Marcus D. Leech:

http://gnuradio.org/redmine/projects/gnuradio/wiki/Guided_Tutorial_GRC
The “bandwidth” setting on the waterfall is just to allow it compute the
of Gnu Radio doesn’t really “know” anything about sample rates–they
are an artifice that only becomes “real” at the edges with actual
hardware, and
also as a convenience when calculating filter parameters.

Hi,
yes ok that is clear so far. And this his how it is described in the
documentation tab. The question arose, because in the tutorial I cannot
explain how the adjustment and the result go together in the pictures.
If you look at the flowgraph in the tutorial the bandwidth is set to
48k, but the X-axis labels in the Waterfall GUI go from -50kHz to 50kHz
implying that the bandwidth might have been set to 100k. I am just
trying to get the basics right.

BR
Mike

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