# Tutorial 2.4.5 The Singing Sine Wave **URL:** \ **Category:** GNU Radio\ **Created:** [August 14, 2015, 10:54pm UTC](https://www.ruby-forum.com/t/tutorial-2-4-5-the-singing-sine-wave/243016 "2015-08-14T22:54:00Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![Sadaf\_N](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/858c86/32.png) [@Sadaf\_N](https://www.ruby-forum.com/u/Sadaf_N)\ **Post date:** [August 14, 2015, 10:54pm UTC](https://www.ruby-forum.com/t/tutorial-2-4-5-the-singing-sine-wave/243016/1 "2015-08-14T22:54:00Z")
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](http://gnuradio.org/redmine/projects/gnuradio/wiki/Guided_Tutorial_GRC) – Scroll to 2.4.5 Best regards Mike ---
**Author:** ![Michael\_Thelen\_DK4M](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/3ab097/32.png) [@Michael\_Thelen\_DK4M](https://www.ruby-forum.com/u/Michael_Thelen_DK4M)\ **Post date:** [August 15, 2015, 1:56am UTC](https://www.ruby-forum.com/t/tutorial-2-4-5-the-singing-sine-wave/243016/2 "2015-08-15T01:56:17Z")
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 > > * * * > > Discuss-gnuradio mailing list > [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) > [Discuss-gnuradio Info Page](https://lists.gnu.org/mailman/listinfo/discuss-gnuradio) > 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. ---
**Author:** ![Michael\_Thelen\_DK4M](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/3ab097/32.png) [@Michael\_Thelen\_DK4M](https://www.ruby-forum.com/u/Michael_Thelen_DK4M)\ **Post date:** [August 15, 2015, 1:57pm UTC](https://www.ruby-forum.com/t/tutorial-2-4-5-the-singing-sine-wave/243016/3 "2015-08-15T13:57:09Z")
Am 15.08.2015 um 01:55 schrieb Marcus D. Leech: > > [http://gnuradio.org/redmine/projects/gnuradio/wiki/Guided\_Tutorial\_GRC](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