LimeSDR transmit woes - RESOLVED

I’ve been playing around with a LimeSDR (firmware/gateware v1.4) for about two weeks now and I’m having trouble transmitting with the LimeSDR device in GNURadio. Here’s the waterfall of the receiver and the transmitter:

Real-time duration of the waterfall is 10 seconds. You can see the transmitter has transmitted about 8 seconds of signal and the dropouts are visible in the received signal. Here is the flowgraph I am using:

I’ve tried several iterations to try and tease out the culprit, unsuccessfully to date:

  • Use a 2.6MHz bandwidth with 8 bit samples and rational resampler (minimum file read/write)
  • Use a 10MHz bandwidth with 16 bit samples (minimum computational requirement)
  • Disable the receive chain (in case the receiver was interrupting the transmitter)
  • Use two different computers (i7 duo and 8 core Xeon) both using USB3.0
  • Use two different environments (GNURadio on Ubuntu 16.04, GNURadio via Pothos on Windows 7)

I have the same issues every time. I am using the latest master branch for LimeSDR and I’ve used GNURadio from the myraidrf PPA and master via PyBOMBS. Within the bursts of data transmission I can confirm my signal (simulated GPS) is coming through. I just need the dropouts to go away.

Looking for help/advise - thanks,

philip hahn

Try disabling the transmit side and receive a known signal source, eg FM band, DVB-T band, etc. Can you view a live waterfall without dropouts? Try using GQRX or SDR# with LimeSDR and play with the sample rate. Can you consistently receive a signal without gaps at various sample rates?

When I’ve had issues such as the one you’re describing, dealing with SDRs pushing data over USB, is that the USB bus cannot handle the sample rate that I’ve requested, and I have to back down the sample rate, usually to 8 MSPS or less.

Hi Mattypiper,

I have the same problem at 10Msps and 5Msps. I can receive a waterfall without any interruptions, both in GNU Radio and GQRX (decoded FM radio plays cleanly). It is only on the transmit side where I am having issues. I can transmit or receive 10Msps with my HackRF no problem (obviously not simultaneously)

Thank you,


@joshblum was able to help me resolve this issue. This issue is captured here: and Josh committed a fix yesterday. This resolves my issue and I can transmit at 10Msps while simultaneously receiving without issue. Thanks Josh!