Lime Mini OSX - RX differences between USB 2 & 3

Macbook Pro - OSX 10.13.4 - 2.5 GHz Intel Core i7 - 16 gb RAM - USB 3.0 Ports

I just received my Lime Mini board a few days ago. I’ve had a few issues so far but, that’s to be expected on OSX. One of the issues I’ve noticed is that when the LimeSDR Mini is plugged into a USB 2.0 cord it receives noticeably more powerful signals than when the board is plugged directly into the USB 3.0 port.

Using USB 3.0

Speed: Up to 5 Gb/sec
Current Available (mA): 900
Current Required (mA): 896

Using USB 2.0

Screen Shot 2018-07-25 at 4.52.46 PM.png
Speed: Up to 480 Mb/sec
Current Available (mA): 500
Current Required (mA): 388

Same antenna and settings were used in both captures. I’ve read that the Lime Mini board needs the power of USB 3.0 to reach optimum working condition so it seems odd that USB 2.0 with less power would result in a much stronger RX signal.

Any ideas?

  1. What you are seeing is noise level.
  2. Your pictures show more intense noise when plugged directly into the USB port.
  3. I conclude that your increased noise is due to the proximity of the LimeSDR mini to your computer. Clearly when your LimeSDR mini is far away from your PC, there is less noise.
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That makes sense but, when I tested this with a USB 3 cord away from the laptop I get similar results. One peculiar thing when I’m using USB 3 is that when I touch the bottom of the board with my hand, the noise level drops significantly and the reception is good.

Hadn’t appreciated that USB 3.0 uses spread spectrum clocking, in an effort to reduce EMI, which may go some way to explaining what you’re seeing.

In my case USB 3.0 is significantly worse than USB 2.0 and this just doesn’t seem right at all. I’ve had the same results inside of VMWare running Ubuntu 16.04. As I posted elsewhere, on my 2015 Macbook Pro I have to unplug and replug after every run of code involving the mini. I’m wondering if these issues could be related in some way. When I’m working inside the Ubuntu VM in VMWare I can at least use the mini without unplugging each time, but the RX issues are still present.

Worse in what respect? As suggested by @frog, seems likely you’re seeing more noise with USB 2.0. Would suggest trying to shield the board and look for known good signals to compare.