QSpectrumAnalyzer seemingly not receiving any data from LimeSDR stock antennas

Hey there.

I’ve been trying to get any real data from my LimeSDR using the stock antennas but as of yet have had no luck. I’m using QSpectrumAnalyzer to try detect any sort of change in Hydrogen lines over the course of a day, but I think I’m only picking up the system noise. I’ve attached a screenshot of the output of QSpectrumAnalyzer over a few hours, it’s pretty clear where the bandwidth hops are and there’s a distinct pattern.

Please let me know if I can post anything else that might help.

I should also add that I’ve disconnected the antennas and run the program with the same settings and noticed no difference.

You are picking RF noise, can be from USB or board it self.
Put the board in proper metal case, ground all 4 ends to case,
use good pigtails and connectors.
Put ferrite cores on both ends of USB 3 cable.
Consider to power Lime from separate DC source with clean output.

Terminate the input with 50 ohm terminator.
Run the same measurement and if the line is not flat, you need
to make your homework again :wink:

I need to learn more about this. I’ve been looking around for the right kind of case and cables.

How much difference does a metal case make? I was about to make a plastic one, thinking it might protect from static discharge.

What’s a good USB 3 Cable and ferrite to use?


Go to IT or electronic hardware shop and buy clip-on ferrites, few
of each brand, and play with them.
Small one can be clipped even on pigtails - that can help too.
Metal case is so called Faraday cage - no RF in, no RF out and even
can be useful for cooling the board.
Here mine in early stage -> 2017 Mar 05

Now have more cooling and fan inside and outside plus pigtails with
N and SMA connectors.

I’ve got the slick aluminum case that the lime comes with, so it’s all pretty closed off. But I suppose I could ground the case. If I open the case up and use a power supply, wouldn’t the USB 3 cable to the computer still supply the same amount of noise?

I feel like, noise or not, removing the antennas should have made some sort of difference.

Hello @Fshkie,

The usual reason for a problem you described is that you didn’t choose an antenna on the software side or choose the wrong one. The antenna is called LNAL if you are connecting the physical antenna to RX1_L (which you suppose to use considering the frequency I see on the screenshot).

UPD: Also consider to try Gqrx instead of QSpectrumAnalyzer. Here is a configuration I’m using:

Please not that as a rule of thumb it’s better to use the latest version of the software, e.g. compiled from the source code. Particularly I didn’t have any luck with Gqrx on Arch Lunux until I switched to source-based gqrx-git package.

I have found that the default settings in QSpectrumAnayzer are not good for the Lime. You have to set the bandwidth significantly larger that the scan rate. So like: Sample Rate 20.000 MHz, Bandwidth 30.000 MHz.

Right, using sample rate / bandwidth / whatever above or below LimeSDR’s limits (or sometimes USB throughput) is another reason why things can not work. Also I would advise to upgrade LimeSDR’s firmware to latest version using LimeUtil.

Hey man, thanks. I actually figured it out a couple days ago, but it was that I wasn’t using the correct antenna. I’ve changed it to LNAL and it’s doing better. I now need to try change the port to RX1_W so that I can see the H line, but they use these damn u.fl connectors, so it’s proving to be a bit of a challenge.

Thank you though.