Artifacts appear and disappear while tuning

Projects LimeSDR
1

Hi everyone!
I have a Limesdr mini v1.2 plugged into USB 3.0 port of my Intel I5-8xxx laptop.
Everything is up-to-date.

I find this… “oddity” while I’m tuning frequencies

error%20limesdr%20mini%201
error%20limesdr%20mini%2011878×659 299 KB

error%20limesdr%20mini%202
error%20limesdr%20mini%2021871×680 321 KB

error%20limesdr%20mini%203
error%20limesdr%20mini%2031865×710 338 KB

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error%20limesdr%20mini%2041877×686 321 KB

error%20limesdr%20mini%205
error%20limesdr%20mini%2051898×688 324 KB

If you look at 30 MHZ, as I tune up those artifacts appear and, while I continue tuning up, they move around appearing and disappearing, covering every signal on that range of frequency. Gains of the board seem affect them too.

I found this fact in other frequencies too.

Around 70 MHZ, I saw these large blocks of artifacts

error%20limesdr%20mini%206
error%20limesdr%20mini%2061870×683 324 KB

They cover every signal and, to see what’s on that band (here just for an example) I should increase sample rate and then tune to a close frequency that leaves a window of non covered signal.

I used SDRAngel, SDR Console, SDR#, Cubic, etc…
on Windows and Linux Manjaro: same effects on same frequencies.
I used a cooler, an FM Broadcast filter, I played with FIR, LP, NCO, SR, DC, IQ.
I changed the antenna (passive), I used laptop plugged to PSU and with battery only.

Same effects on same frequencies.

This is the second board that I have changed, LimeQuickTest is passed, SDR Console and HDSDR tell me that board is calibrated every time.

I would thank everyone, guys!
I need to solve this.

Thank you

Paq

2

Do you have a low pass filter installed after the antenna. Maybe those blocks can be images of strong nearby digital stations? Do they disappear if you unplug the antenna/turn down the gain?

3

I have the FM Broadcast stop only. Actually I tried just today to spot what they could be, and they seems to be like 3 Dvb-t mux next to 174,5 mhz…

If I unplug the antenna or I use the Lna gain they disappear.

4

Well then I’m compelled to say that those are images of strong stations that you receive out of band, and that is expected behaviour. As LimeSDR does not have any kind of tracking RF filters, you might want to invest in buying or DIY-ing your own ones for the frequency ranges of your application.

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5

Thank you. I will try a filter asap and I will try to modify the board and keep it cool with active fan too.

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6

I would suggest you use soapy driver and gqrx to see if that yields a difference. SDRAngel has some strange behavior but is more powerful and complicated. Did you do an HF mod to your Lime? What signals are you looking for there? It looks more like EMI than radio harmonics to me for sure. Try shutting everything in your house off to find the culprit. Also you’re not utilizing the decimation feature in these screen shots.

7

I used Gqrx and soapy as well obtaining same things. My board, drivers and software are vanilla, so without modifications.
I saw those interferences are similar to the Broadcast TV muxes just next 2 meters band. They are from local tv’s just 16 kilometers far away.
I’m interested in everything below the FM.

8

@Paq
I did Easy Fix 1 for now on Rx1 and it makes a tremendous difference compared to Rx2 Low. Take a look at this for below 100 mhz…
https://myriadrf.org/news/optimising-limesdr-matching-hf/

9

But is this fix valid for the Mini version?
It seems it’s talking about the bigger Limesdr.

10

It is and not sure it’s needed or should be attempted on the Mini.

1 Like