Day 1 with LimeSDR, -47dBFS signal at whatever tuned frequency?

Hi all!

Just received my LimeSDR, got some luck getting it to work, but I’m seeing some weird issues that I haven’t read on this forum yet.

Whatever frequency that I tune to, I am getting a (DC?) signal, and no matter what settings I change it won’t go away. The radio itself would still pick up signal, but I presume because of this strong signal some sort of AGC I am not able to pick them up very well.

Anyone experienced this before?

Note the yellow line in the middle at the bottom of waterfall, I wasn’t transmitting anything at that time. And the same line is present at whatever frequency I tuned to.


Take a look here

1 Like

A solid vertical line is the usual 1/f noise and DC imbalance between the I and Q ADC’s (it is a hardware issue with almost all SDR hardware, but it can be reduced in software by creating a calibration database ( ref : What about IQ imbalance - DC offset calibration? - I would not run the script suggested in that thread, because it is out of date, I would wait until Lime release an updated calibration tool ).

The more worrying thing in the image for me are the blurred horizontal flares, I do not know exactly what you would call them, but they usually would indicate data loss, so it looks like either your USB port is being shared with many other devices causing dropped USB packets, or something else that is causing data to be lost. Your sample rate is somewhere around ~240KSPS which is going to generate about 720KB/sec (I x 12 bit + Q x 12bit samples packed by the FPGA) which does not sound like it could saturate a USB bus (even a shared one). Maybe the data loss is due to a CPU issue, what is the CPU in the machine ?

EDIT: Actually looking at how little spectrum you are looking at, it looks more like an actual signal, so scratch my whole second paragraph.

Thanks 9a4db and mzs,

Thanks for the link, I’ve taken a good look at the article and as suggested by mzs this one seems to be half broken and needs some work from Lime.

I’ve seen people with fairly clean spectrogram (as below), is there something wrong with my LimeSDR, or am I doing something differently?