LimeSDR not transmitting properly on USB 2.0, delays when on USB 3.0

Hello all,

I have a LimeSDR-USB v1.4s. I’ve been trying to experiment with transmission using this simple flow in GRC:

With the centre frequency at 200MHz, using the GUI slider I can generate a tone at 200MHz +/-250kHz.

I’ve been testing this program on two machines:

  • An older desktop PC (i7 920, 18GB RAM, USB 2.0 ports, ASUS P6T Deluxe v2 motherboard).
  • A newer laptop (i5-6200U, 8GB RAM, USB 3.0 ports, HP Pavilion 14).

Both systems are running Ubuntu 19.04, and the various SDR software packages were all downloaded from the ubuntu repositores:

  • GNU Radio companion
  • LimeSuite Library Version: v18.06.0+dfsg-1build1
  • LimeSDR Firmware 4, Hardware 4, Gateware 2.17.
  • SoapySDR v0.6.1-4

LimeQuickTest seems to run OK, and the outputs of the Quick Test ( seemed to be OK, so it looks like the hardware is fine.

Unfortunately, I’ve been running into two problems:

  • On my desktop PC with USB 2.0 ports, my flow seems to freeze when I try to transmit, and I just get the centre frequency visible on the spectrum analyser. Moving the GUI slider doesn’t update the frequency. The GUI frequency sink also freezes despite moving the slider. This doesn’t happen on my laptop with USB 3.0 ports.
  • On my laptop, there is a long delay (about 16 seconds) between changing the tone frequency using the GUI slider and the RF output being updated as seen on the spectrum analyser.

What could be causing these problems?

So, the USB problem has been solved by download the latest LimeSuite from the myriadrf ppa. In my case, because I’m running Ubuntu 19.04 Disco and the ppa doesn’t support Disco, I had initially installed the version in the Ubuntu repositories, but that is quite old. After modifying the ppa to pull from the bionic distro (see how to here), I’m now running LimeSuite v19.04.0-myriadrf1~bionic. Now my USB 2.0 PC can transmit just fine.

However, I am still running into the strange 16 second delay issue with the GRC flow mentioned above. I’d love to understand the reason for that.

Any thoughts on the delay issue?

My only advice is to start an Osmocom Source.
I hear that the Lime needs a Receive block to sync the USB packets.