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Re: [Discuss-gnuradio] Questions about the qt frequency display.

From: Stefan Gofferje
Subject: Re: [Discuss-gnuradio] Questions about the qt frequency display.
Date: Mon, 02 May 2011 13:32:03 +0300
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On 05/02/2011 01:04 PM, Tom Rondeau wrote:
>> I ran an audio_source -> qtgui_sink and it looked fine to me. I also
>> took your grc xml here and ran that and saw the four spikes as expected.
>> The setting of the center frequency is only to set the axis labels, it
>> won't do any translating of the signal or anything. Remember in this
>> case and with your audio source one, the signal is real, so you will
>> only have spectral components from -22.05 to 22.05 kHz and the spectrum
>> will be symmetric around 0 Hz. So "translating" this up to 22.05 kHz
>> won't really do anything for you since you have no information over
>> 22.05 kHz, anyways.

I had some off-list conversation with Marcus and I think, I'm getting a
hang of this complex vs. real stuff. Higher math is some 20 years ago
for me :).

However, I wonder, what's the sense of treating real streams like
complex, and mirroring them.
In the project I have in mind with GNURadio, there would be a
requirement for a spectrum / waterfall display of the NF signal to look
for anything out of the ordinary, especially signals that would be
unhearable on normal receivers because the NF stage would filter them
out. It goes into the direction signal analysis/SIGINT.

Would it make sense, if the display is set to float, to actually show 0
- - $BANDWIDTH? I got the WX-stuff running (= it doesn't segfault but it
eats 100% CPU, so it doesn't react to anything) and the WX-FFT display
does show 0 - $BANDWIDTH/2.

That's just a suggestion, of course. I'm just imagining that there might
be a few others out there which are also used to analog NF spectrum
displays which show 0 - $BANDWIDTH :).

- -S

- -- 
 (o_   Stefan Gofferje            | SCLT, MCP, CCSA
 //\   Reg'd Linux User #247167   | VCP #2263
 V_/_  Heckler & Koch - the original point and click interface
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