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