# How to choose the right sampling rate and bandwidth for RTL-SDR dongle?

Receiving the frequency of 97.9 MHz

I have a Terratec SDR dongle and I am trying to capture a radio frequency. The FFT window shows the frequency range from -500 to 500 KHz. Is there a way to increase this or it depends on the dongle and is fixed? Does it depend on the sampling rate?

It's important to understand that in DSP (and in GNU Radio especially), things are always only handled with respect to samples – e.g. a sine with a period of three samples would have frequency $\frac13$, no unit. The spike on the FFT plot would be at $2 \cdot \frac 13= \frac23$ of the axis (factor of two: your Nyquist zone is from $-\frac{f_\text{sample}}{2}$ to $+\frac{f_\text{sample}}{2}$).
How that $\frac 13$ relates to real world frequencies is defined by the sampling rate of the analog-to-digital (or digital-to-analog, in TX) converter.