I am new at this. I am using a Raspberry Pi 3 B + with the LimeSDR Mini. I am trying to create a WBFM transmitter at a frequency of 510 MHz using GNU Radio. The problem is the transmitted signal (1KHz tone), I do not know if I’m using the wrong parameters in GNU Radio or it’s Lime Mini. I see two signal peaks occur around my fundamental frequency when I start transmitting. How could I solve this? If someone can help me and explain a little about this. I am using the RTL-SDr to receive the signal in SDR #. Here I leave the images of the blocks in GNU Radio and what I receive in SDR #.
What OS are you using?
I’m using Raspbian in the Raspberry Pi 3 B +
Try adjusting the sampling rate in the LimeSuite Sink block. It should match the 441k rate you get as the output of WBFM Transmit block
Still the same problem, even changing the sampling frequency of the LimeSuite Sink block to 441KHz
I would have used the NBFM TX example, given as part of gr-limesdr ( https://github.com/myriadrf/gr-limesdr/tree/master/examples ) called FM_transmitter.grc, as a starting point. It is transmitting a 480kHz wide signal but using a Rational Resampler block so that the LimeSDR can transmit at 2MSPS which at a guess may be a lower limit to the TX sample rate
I don’t have a LimeSDR where I am right now, so added a throttle block to stop 100% CPU usage, you would remove that block if you had an actual hardware sink in your flow graph. And I also added a second rational resampler to deal with your non-studio quality incoming 44.1kHz sample rate, this increased the processing, but it was at the lowest sample rate in the flowgraph. So less overhead than trying to deal with it at higher sample rates. I also could have chosen a final sample rate of 2.205MSPS on the LimeSDR either to reduce the processing overheads.
Ok! This is the new test but I still have the same problems, this could be solved if I use a low pass filter at the output of the LimeSDR Mini. Will it be an intermodulation problem?
The bandwidth of the signal looks about right (slightly less than 500kHz). But I’ve never used a USB 2.0 port or RPi hardware, so I’m running out of ideas.
I’d load the NBFM example from https://github.com/myriadrf/gr-limesdr/tree/master/examples and compare all the settings in the gr-limesdr blocks between the two flowgraphs. And maybe test if it has the same issue, just point it at a 48kHz wave file and run.