UPDATE: 4 RTL-SDRs with 8.4 MHz bandwidth in gqrx

After I managed to combine 2 dongles for an FFT in gnuradio, I wanted to pipe the output to gqrx and add 2 more dongles to the flowgraph. Due to the cut-off at the edges of each dongle, we get 8.4 MHz bandwidth, but since the rational resampler only supports integer values, our sample rate is 4*2.4e6 = 9.6. Use interpolation=35 and decimation=10 for the true sample rate of 8.4 MHz. I updated the 8.4 MHz flowgraph at the bottom of the page.

You can even listen to analog signals, that are at the overlapping areas!

8.4 MHz sample rate:

8.4_rtlsdr

9.6 MHz sample rate (8.4 MHz bandwidth) with old flowgraph:

9.6_rtlsdr

At first you need to create a fifo file with this command: mkfifo /tmp/fifo_gqrx

Use this settings in gqrx (change ‘freq’ to the value of center_freq in grc): file=/tmp/fifo_gqrx,freq=100e6,rate=9.6e6,repeat=false,throttle=false

Also make sure, that you set the center frequency in gqrx.

You might have to open gqrx some times if it crashes on startup, but it will work!

Here are the grc-files:

4.4 MHz (4.8 MHz sample rate)

8.4 MHz (8.4 MHz sample rate)


Comments

  1. I have 3 different types of RTL dongles consisting of an R820T2, E4000, and FC0013 tuner chips. can these be made to work with the multi tuner code, or must all the tuner chips be the same?

  2. This is fantastic! Thank you for posting. I will be attempting to imitate this asap.

  3. Hi!
    Sorry for my English.
    You could make a plugin for SDR #?
    It would be great!

  4. Sorry for the late reply…
    I doesn’t matter, what types of tuners you have; I used 3 different tuners in the example above.
    A plugin for SDR# would be great, but I have no idea of how to write it.

  5. I’m studying a little gnuradio but I feel like some easy documentation is missing…
    how did you came up to the value of 35 for interpolation and 10 for decimation?
    can you write down a simple formula (if it’s simple :P)?
    thanks

  6. oops I see, 2.4/10*35=8.4 :)

  7. Exactly! I actually never thought about documenting this because of it’s obviousness ;)

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