# Very high spurious emission during the LimeSDR mini calibration

**URL:** <https://discourse.myriadrf.org/t/very-high-spurious-emission-during-the-limesdr-mini-calibration/8052>\
**Category:** LibreCellular\
**Created:** [6 October 2023 18:28 UTC](https://discourse.myriadrf.org/t/very-high-spurious-emission-during-the-limesdr-mini-calibration/8052 "2023-10-06T18:28:15Z")\
**Posts on this page:** 9\
**Page:** 1

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**Author:** ![sindi](https://yyz2.discourse-cdn.com/flex034/user_avatar/discourse.myriadrf.org/sindi/32/4194_2.png) [@sindi](https://discourse.myriadrf.org/u/sindi)\
**Post date:** [6 October 2023 18:28 UTC](https://discourse.myriadrf.org/t/very-high-spurious-emission-during-the-limesdr-mini-calibration/8052/1 "2023-10-06T18:28:15Z")

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Hi everybody,

I have tested the LimeSDR mini (the old and new version) in the LTE eNB from srsRAN and openairinterface5G. In figure 1, there is the spectrum when running the LTE eNB from [User Guide — LibreCellular 21.04 documentation](https://librecellular.org/user/index.html) srsRAN after the LimeSDR calibration is finished. As shown, the spectrum seems OK after the calibration is finished. However, during the calibration, a lot of spurious appear in the spectrum as shown in figure 2 (span of 3 GHz) and figure 3 (span of 54 MHz). In those tests, I used tx\_gain = 53 and an attenuator of 30 dB at the output of the LimeSDR mini. So, the power of those spurious is high, around 6-8 dBm. The results are similar when I use soapy or eNB from openairinterface5G, with LimeSDR v.1 or LimeSDR v.2. I am concerned that these spurious can damage the power amplifiers like ZHL-1000-3W+ from minicircuits ([Connectorized SMA, High Power Amplifier, 500 MHz to 1000 MHz, 50Ω | ZHL-1000-3WX+ | Mini-Circuits](https://www.minicircuits.com/WebStore/dashboard.html?model=ZHL-1000-3WX%2B)) whose absolute maximum rating input RF power is 0 dBm. So, I would be very grateful if someone can give me a direction how to minimize those spurious during the LimeSDR mini calibration process. Best regards, Sindi.

 ![Figure 1-Spectrum after calibarion is finished](https://canada1.discourse-cdn.com/flex034/uploads/myriadrf/original/2X/5/5091680df634585af8dd461c0239f852cb8c946f.jpeg)

 ![Figure 2-Spectrum with 3GHz span during the calibration](https://canada1.discourse-cdn.com/flex034/uploads/myriadrf/original/2X/f/f24f0bf7878d5f16348c79dd1b8cf17f269ce007.jpeg)  
 ![Figure 3-Spectrum with 54.78 MHz span during the calibration](https://canada1.discourse-cdn.com/flex034/uploads/myriadrf/original/2X/6/605d6cbc84db75132c2dc308b75801f3af226151.jpeg)

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**Author:** ![RightHalfPlane](https://avatars.discourse-cdn.com/v4/letter/r/46a35a/32.png) [@RightHalfPlane](https://discourse.myriadrf.org/u/RightHalfPlane)\
**Post date:** [7 October 2023 01:07 UTC](https://discourse.myriadrf.org/t/very-high-spurious-emission-during-the-limesdr-mini-calibration/8052/2 "2023-10-07T01:07:18Z")

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> [@sindi](#):
>
> spurious

I have found with most of the SDR transmitters. When you are driving it with floating point data - if the input voltage to the SDR transmitter is even slightly greater than ± 1.0 volts they generate spurious emissions. I am not sure if that applies during calibration.

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**Author:** ![adim](https://avatars.discourse-cdn.com/v4/letter/a/8edcca/32.png) [@adim](https://discourse.myriadrf.org/u/adim)\
**Post date:** [7 October 2023 06:47 UTC](https://discourse.myriadrf.org/t/very-high-spurious-emission-during-the-limesdr-mini-calibration/8052/3 "2023-10-07T06:47:46Z")

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I’d like to know the answer to this as well. OP, have you considered a limiter?

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**Author:** ![adim](https://avatars.discourse-cdn.com/v4/letter/a/8edcca/32.png) [@adim](https://discourse.myriadrf.org/u/adim)\
**Post date:** [9 October 2023 12:34 UTC](https://discourse.myriadrf.org/t/very-high-spurious-emission-during-the-limesdr-mini-calibration/8052/6 "2023-10-09T12:34:38Z")

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Normally you’d have some kind of software control of the PA so you’d only enable it once the calibration procedure is done. But if the calibration occurs outside of normal operations then I’d use a limiter.

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**Author:** ![sindi](https://yyz2.discourse-cdn.com/flex034/user_avatar/discourse.myriadrf.org/sindi/32/4194_2.png) [@sindi](https://discourse.myriadrf.org/u/sindi)\
**Post date:** [9 October 2023 12:55 UTC](https://discourse.myriadrf.org/t/very-high-spurious-emission-during-the-limesdr-mini-calibration/8052/7 "2023-10-09T12:55:22Z")

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OK. Thank you.

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**Author:** ![sindi](https://yyz2.discourse-cdn.com/flex034/user_avatar/discourse.myriadrf.org/sindi/32/4194_2.png) [@sindi](https://discourse.myriadrf.org/u/sindi)\
**Post date:** [9 October 2023 12:59 UTC](https://discourse.myriadrf.org/t/very-high-spurious-emission-during-the-limesdr-mini-calibration/8052/8 "2023-10-09T12:59:08Z")

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Hi,  
I think not, because the power level of those spurious does not change if I change the tx\_gain. Even with a low tx\_gain such as 40, the power level of the spurious is aproximately the same as with tx\_gain = 53. It decreases in the operation frequency only…  
Best regards, Sindi.

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**Author:** ![sindi](https://yyz2.discourse-cdn.com/flex034/user_avatar/discourse.myriadrf.org/sindi/32/4194_2.png) [@sindi](https://discourse.myriadrf.org/u/sindi)\
**Post date:** [9 October 2023 13:00 UTC](https://discourse.myriadrf.org/t/very-high-spurious-emission-during-the-limesdr-mini-calibration/8052/9 "2023-10-09T13:00:05Z")

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Hi,  
I had not considered a limiter, but I will consider it now. Thank you.

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**Author:** ![andrewback](https://avatars.discourse-cdn.com/v4/letter/a/22d042/32.png) [@andrewback](https://discourse.myriadrf.org/u/andrewback)\
**Post date:** [10 October 2023 08:03 UTC](https://discourse.myriadrf.org/t/very-high-spurious-emission-during-the-limesdr-mini-calibration/8052/10 "2023-10-10T08:03:21Z")

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> [@adim](#):
>
> Normally you’d have some kind of software control of the PA so you’d only enable it once the calibration procedure is done

Also be careful of providing a signal input to amplifiers which are not powered up, as this has the potential to damage them. Ideally you would switch the SDR output between a termination and amplifier input.

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**Author:** ![sindi](https://yyz2.discourse-cdn.com/flex034/user_avatar/discourse.myriadrf.org/sindi/32/4194_2.png) [@sindi](https://discourse.myriadrf.org/u/sindi)\
**Post date:** [10 October 2023 17:01 UTC](https://discourse.myriadrf.org/t/very-high-spurious-emission-during-the-limesdr-mini-calibration/8052/11 "2023-10-10T17:01:13Z")

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Hi Andrew,

Ok, thank you very much for the tips. Best regards, Sindi,