Multichannel coherent download
The first step is to develop the necessary hardware and software requirements for coherent multichannel iq sample record.
In order guarantee fast development process the software codes are written in python . A python wrapper for librtlsdr written by Roger can be found here: https://github.com/roger-/pyrtlsdr. Using this API the RTL-SDR dongles are accessible from python.
The continuous sample download is tested with a single dongle and an external signal generator. The output frequency of the generator is set to 800 MHz and -40 dBm, The generator output is connected to the input of the RTL SDR and several consecutive download request have been sent to the device driver. By plotting the consecutive downloaded buffer contents one can check the continuity of the signal samples. The figure bellow shows the joined signal fractions.
The code used for the sample download and plot can be found at the bottom of the page.
Also note that the fist download chunk of the signal samples mostly contains quasi zero values, thus they were discarded. See Figure 2.
The spectrum of the downloaded signal can be seen in Figure 3.
Simultaneous download from multiple RTL SDR:
The previously used code has been extended in order to support the management of multiple RTL SDRs. The code can be found here.
To test the its operation a signal generator operating at 450 Mz with -40dBm output power has been connected to a matched two way power divider. The outputs of the power divider are connected to the inputs of two RTL SDR receivers. Note that these receivers are not synchronized in any sense, they operate individually from different reference clocks. The spectrums of the downloaded signals are illustrated in Figure 4. Some records can be also accessed at the bottom.