Lime mini: RX issue with 100MHz and harmonics

Good afternoon @Zack,

A signal of 100MHz with harmonics is found at the RX input. See Spectrum Analyser screen grab when RX is connected to it.
RX connected to Spectrum Analyser Input
TX with 30dB load connected to spectrum analyser (not used)

center frequency 100MHz

Also test fail.
->Start time: Tue Mar 19 23:38:30 2019
->Device: LimeSDR Mini, media=USB 3, module=FT601, serial=1D424C3C64FD34, index=0
Serial Number: 1D424C3C64FD34
[ Clock Network Test ]
->REF clock test
Test results: 7380; 20577; 33774 - PASSED
->VCTCXO test
Results : 6711012 (min); 6711169 (max) - PASSED
->Clock Network Test PASSED
data: 18 07 26 18 07 26 2
[ 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 ]
->Configure LMS
->Run Tests (TX_2 -> LNA_W):
->On board loopback test:
Test 1:(SXR=1000.0MHz, SXT=1005.0MHz, TXPAD=8): Result:(-46.8 dBFS, 5.00 MHz) - FAILED
->Configure LMS
->Run Tests (TX_1 -> LNA_H):
->On board loopback test:
Test 1:(SXR=2100.0MHz, SXT=2105.0MHz, TXPAD=8): Result:(-46.5 dBFS, 5.00 MHz) - FAILED
->RF Loopback Test FAILED
=> Board tests FAILED <=
Elapsed time: 4.90 seconds

Lime Suite GUI allows me to tune output signal and this does not interfere with RX.

The reception works, I can receive FM broadcast station as they are strong.
I try with a homemade probe to get signal at the RX stage but difficult as the FM signal is all over.

Any Idea of the problem?

Regards, Stef

Hi @stef,

It clearly indicates that there is an issue with RF part. It considered to be OK down to ~22dBFS, but -46dBFS clearly indicates an issue. Check matching network components, maybe some of them are damaged.

Hi @Zack

I looked at the board RF part on binocular magnifier with no specific finding.
Looking at the schematic the Sky13411 IC3 IC4 and VT3 RF MOSFET are involved on the Loopback RF part if I am not wrong.

Where in Lime Suite GUI I can control RFSW TX and RX level for both IC3 and IC4 and as well for TX LB SH to do a try?

I connected the Lime RX to another RX SDR, see the result below:
RX SDR nothing connected

Lime RX connected to RX SDR

We see clearly 100MHz signal, it exists also at 200, 300, 400MHZ …

And now with FFT app running

It shows a lot of signal coming out of the RX input.

Is it normal?

How can I start to troubleshout the problem?

Looking forward for your assistance.
Thanks, Stef

Hi @Zack,

Is it worth to change RFSW_TX and RX, SKY13411-374LF?
Or for the VT3 RF MOSFET?
Could you advise the MOSFET Type?

What is the main problem found when the loopback test failed, especially with -46dBFS?
Which component has to be replaced?

Hi @Zack

Could you advise on how to fix the RF problem?

Could you explain what is the RMA and how it works?


I can not answer this question. Every component in the chain, including LMS7002M may be affected.

Contact Crowd Supply for more details, please.

Connect to the board with LimeSuiteGUI, then go to menu item Modules → Board controls. Here you will find “RX RF port parg” and “TX RF port path” , “Loopback” controls.