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I'm trying to visualize the frequency band utilization during a GSM phone call using SDR. Ideally, I would like to plot the whole 900 MHz range, i.e. 876-959 MHz. However, even setting the zoom to the minimum I'm only getting a band of about 2 MHz on display (here: 899-901 MHz):

enter image description here

How can I display a wider frequency band on the spectrum analyzer and waterfall graphs?

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    $\begingroup$ Hello Dmitry, and welcome to ham.stackexchange.com! $\endgroup$
    – rclocher3
    Sep 19 at 23:32
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Unfortunately you cannot increase the bandwidth much: the sampling rate in RTL2832U is at maximum 3.2 megasamples / second. In theory (Nyquist theorem) you could get ±1.6 MHz banwidth, but that is already pushing the limits of your hardware. The ± in the bandwidth comes from the fact that you are sampling the I and Q, or signals with a 90° phase shift separately.

If you don't need real time data, you could try to sample 2 MHz at a time and then patch these samples together. I have played around with the post-processing in Python, so let me know if you are interested?

I just found out that there's a RTL-SDR scanner project that samples spectrum piece by piece. This of course won't give you the waterfall view.

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  • $\begingroup$ Thanks, I'll try the RTL-SDR scanner. Do you by chance know of any common hardware that is able to capture more samples per second and thus allow to analyze a wider frequency band in real time? $\endgroup$ Sep 20 at 5:51
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    $\begingroup$ I don’t have experience with any of the high end SDRs, but for example Ettus USRP X300 seems to offer over 100 MHz bandwidth. Also the price is a few orders of magnitude higher than for the RTL-SDR. $\endgroup$
    – OH2FXN
    Sep 20 at 13:30
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If you use SDRSharp with an Airspy Mini, instead of an RTL-SDR, the supported sample rates allow up to 6 MHz bandwidth, due to the use of an ADC with a higher sample rate than the RTL2832 is capable of.

For a wider bandwidth display than 6 MHz, you either need to use different software that can scan or stitch across a frequency range, instead of directly capturing that entire range at once, and/or more specialized hardware (such as Ettus USRP or LimeSDR units, and/or PCi bus SDRs) which can support higher sample rates and data bandwidths.

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HackRF One will give you 20MHz bandwidth. Edit for more detail: If you buy the HackRF One instead of the Noelec SDR dongle, you will have 20MHz instead of 2MHz. Note that the HackRF One costs about $300 which is still 10 times cheaper than a spectrum analyzer but 15 times more expensive than the SDR dongle you currently have.

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    $\begingroup$ Hello and welcome to ham.stackexchange.com! Thanks for the answer, but would you please expand it a bit? Would Dmitry need to do anything else besides change the hardware? Please edit your answer to include more information, rather than putting the information in a comment. $\endgroup$
    – rclocher3
    Sep 20 at 14:33

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