LimeSDR transmission issues

Greetings, I’m attempting to establish a 2-way data streaming connection across SDRs and the LimeSDR seemed like a good choice on paper. Unfortunately, I’ve been trying for a few days and have been unable to reliably transmit any data off the Lime. I’m using QPSK modulation w/ GNURadio (though I have tried BPSK with similar results).

All of the tests below are using the default antennas that come with the Lime and the SDRs are a few feet apart.

From the following images you can see that when transmitting data with the HackRF, both the Lime and the Blade can correctly demodulate the signal (and data is correctly decoded) - I experienced almost no data loss.

Transmitting with the Blade gave similar results. Data loss rate was still very low.
51 PM
However, when transmitting data with the Lime the demodulated constellation is incredibly noisy (80-90% data loss rate) or not even discernible.

Both Limes have passed loopback tests and I have tried using different transmit channels, different frequencies, and different antennas all with the same result. I know the Limes are functional since I’ve successfully run Osmocom GSM stacks on both of them so I’m completely stuck on what could be going wrong.

Also, is the geometrical difference in the received/transmitted signal with the Hack vs. Blade/Lime (the circle shape vs. more distinct constellation) due to the HackRFs lower data transfer rate or something else?

Hi, @tgern

Are you using gr-limesdr blocks? Could you share your flow graphs?

Yes, I am using gr-limesdr! Sure, qpsk_transceive.grc

I had built most of the transceiver myself before running into a few issues and decided to merge with Dan CaJacob’s work. I had the same issues before integrating his blocks so I don’t believe they are the issue. Right now I’m simulating a remote connection between two computers with the two tun/tap interfaces.

For reference I’m running this on a 2015 MacBook Pro inside a Kali VM in virtualbox.



Are you using calibration? Have you tried changing gains? Which boards are you using?

P.S. Usually calibration needs maximum gain values.

Yes, I tried using calibration with variable gains and it looks about the same. This is less than a foot away with calibration on (10MHz bandwidth) and gain set at 50dB. I have also tried 60dB gain with similar results.

I am using two LimeSDR-USBs.

do you have the code for operating the transmission/reception through LimeSDR’s