# Lime USB - Failed Loopback Test

**URL:** <https://discourse.myriadrf.org/t/lime-usb-failed-loopback-test/6996>\
**Category:** LimeSDR\
**Created:** [4 March 2021 16:12 UTC](https://discourse.myriadrf.org/t/lime-usb-failed-loopback-test/6996 "2021-03-04T16:12:38Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![whzrf](https://avatars.discourse-cdn.com/v4/letter/w/839c29/32.png) [@whzrf](https://discourse.myriadrf.org/u/whzrf)\
**Post date:** [4 March 2021 16:12 UTC](https://discourse.myriadrf.org/t/lime-usb-failed-loopback-test/6996/1 "2021-03-04T16:12:38Z")

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Hi,  
Right out of the box from Crowdsupply a couple of months ago. I followed the instructions to install LimeSuite on Ubuntu I updated the board and when LimeQuickTest…Any thoughts on why?

[TESTING STARTED]  
-\>Start time: Thu Mar 4 11:09:17 2021  
-\>LimeSuite version: 20.10.0-g1480bfea

-\>Device: LimeSDR-USB, media=USB 3.0, module=FX3, addr=1d50:6108, serial=00090726074F2D11, HW=4, GW=2.23  
Serial Number: (BLANK)  
Chip temperature: 27 C

[Clock Network Test]  
-\>FX3 GPIF clock test  
Test results: 28731; 32487; 36243 - PASSED  
-\>Si5351C test  
CLK0: 17554 / 17554 - PASSED  
CLK1: 17554 / 17554 - PASSED  
CLK2: 17554 / 17554 - PASSED  
CLK3: 17554 / 17554 - PASSED  
CLK4: 17554 / 17554 - PASSED  
CLK5: 17554 / 17554 - PASSED  
CLK6: 17554 / 17554 - PASSED  
-\>ADF4002 Test  
Result: 10 - PASSED  
-\>VCTCXO test  
Results : 5113013 (min); 5113146 (max) - PASSED  
-\>Clock Network Test PASSED

[FPGA EEPROM Test]  
-\>Read EEPROM  
-\>Read data: 12 07 1A 12 07 1A 02  
-\>FPGA EEPROM Test PASSED

[LMS7002M Test]  
-\>Perform Registers Test  
-\>External Reset line test  
Reg 0x20: Write value 0xFFFD, Read value 0xFFFD  
Reg 0x20: value after reset 0x0FFFF  
-\>LMS7002M Test PASSED

[RF Loopback Test]  
Note: The test should be run without anything connected to RF ports  
-\>Configure LMS  
-\>Run Tests (TX\_2-\> LNA\_L):  
CH0 (SXR=800.0MHz, SXT=805.0MHz): Result:(-14.8 dBFS, 5.00 MHz) - PASSED  
CH1 (SXR=800.0MHz, SXT=805.0MHz): Result:(-16.2 dBFS, 5.00 MHz) - PASSED  
-\>Run Tests (TX\_1 -\> LNA\_W):  
CH0 (SXR=1800.0MHz, SXT=1805.0MHz): Result:(-19.7 dBFS, 5.00 MHz) - PASSED  
CH1 (SXR=1800.0MHz, SXT=1805.0MHz): Result:(-22.6 dBFS, 5.00 MHz) - FAILED  
-\>Run Tests (TX\_2-\> LNA\_H):  
CH0 (SXR=2500.0MHz, SXT=2505.0MHz): Result:(-17.2 dBFS, 5.00 MHz) - PASSED  
CH1 (SXR=2500.0MHz, SXT=2505.0MHz): Result:(-13.3 dBFS, 5.00 MHz) - PASSED  
-\>RF Loopback Test FAILED

=\> Board tests FAILED \<=

Elapsed time: 1.74 seconds

It looks like (TX\_1 -\> LNA\_W) CH1 is the one that caused the failure. Any thoughts on the cause and fix?

Thanks!!

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<div class="post-metadata">

**Author:** ![mzs](https://yyz2.discourse-cdn.com/flex034/user_avatar/discourse.myriadrf.org/mzs/32/2678_2.png) [@mzs](https://discourse.myriadrf.org/u/mzs)\
**Post date:** [4 March 2021 19:23 UTC](https://discourse.myriadrf.org/t/lime-usb-failed-loopback-test/6996/2 "2021-03-04T19:23:48Z")

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> [@whzrf](#):
>
> CH1 (SXR=1800.0MHz, SXT=1805.0MHz): Result:(-22.6 dBFS, 5.00 MHz) - FAILED

My very basic understanding of that test is that it is a loopback test where the transmitter of channel 1 in this case is tuned to a frequency of 1805 MHz, and told to transmit a signal (CW at a guess), and the RX channel 1 is told to receive at 1800MHz. And the result is what signal level is seen by RX and at what frequency offset. In this case -22.6dBFS is the signal level seen at a frequency offset of +5.00MHz. A pass at all the frequencies used in the loopback tests is defined as a signal level of -9.00 to -21.00 dBFS (or [-15](https://github.com/myriadrf/LimeSuite/blob/master/QuickTest/LimeSDRTest_USB.cpp#L149) dBFS with a tolerance of +/- [6 dB](https://github.com/myriadrf/LimeSuite/blob/master/QuickTest/LimeSDRTest.cpp#L334))

So your LimeSDR is working, but on those ports it means one of a two things the TX power is either a bit less than expected at that frequency, or the RX sensitivity is a bit lower than expected at that frequency. The loopback as far as I’m aware, on the ports that are 1.6dB outside specification (TX\_1 → LNA\_W channel 1), is internal to the LMS7002M chip.

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<div class="post-metadata">

**Author:** ![whzrf](https://avatars.discourse-cdn.com/v4/letter/w/839c29/32.png) [@whzrf](https://discourse.myriadrf.org/u/whzrf)\
**Post date:** [5 March 2021 17:23 UTC](https://discourse.myriadrf.org/t/lime-usb-failed-loopback-test/6996/3 "2021-03-05T17:23:54Z")

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Gotcha. Thanks for the Info. I guess, leave as is? or should i get an RMA from CrowdSupply? @andrewback

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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:** [6 March 2021 15:52 UTC](https://discourse.myriadrf.org/t/lime-usb-failed-loopback-test/6996/4 "2021-03-06T15:52:21Z")

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It’s working, but as noted by @mzs, a little bit out of spec. Assuming that you had nothing connected to the RF ports — as this can skew results — you may want to consider RMA.