As the title states, I’m running into this error while running a communications system on loopback.
The TX power seems to jump all over the place without changing any gain values. I’ve seen readings as low as -65dBm and as high as -40dBm. The system is running in PothosFlow, and has very little room to increase gain without encountering a high BER. I’ll include a picture of the FFT viewer loopback test, as the readings for that also seem incredibly low in relation to other pictures of the test I’ve seen.
I should also note that I’m taking my power readings with an oscilloscope, and go against the readings that are visible in PothosFlow with a periodogram block.
Any help would be appreciated, as I would like to rule out any possibility of a hardware defect as soon as possible.
Here are LimeQuickTest results as well.
[ TESTING STARTED ]
->Start time: Wed May 19 13:24:47 2021
->LimeSuite version: 20.10.0-g1480bfea
->Device: LimeSDR Mini, media=USB 3.0, module=FT601, addr=24607:1027, serial=1D4C1F7F64AFAA, HW=2, GW=1.30
Serial Number: 1D4C1F7F64AFAA
Chip temperature: 53 C
[ Clock Network Test ]
->REF clock test
Test results: 53083; 749; 13940 - PASSED
->VCTCXO test
Results : 6711066 (min); 6711219 (max) - PASSED
->Clock Network Test PASSED
[ FPGA EEPROM Test ]
->Read EEPROM
->Read data: 13 02 0B 13 02 0B 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 ]
->Configure LMS
->Run Tests (TX_2 -> LNA_W):
CH0 (SXR=1000.0MHz, SXT=1005.0MHz): Result:(-19.0 dBFS, 5.00 MHz) - PASSED
->Run Tests (TX_1 -> LNA_H):
CH0 (SXR=2100.0MHz, SXT=2105.0MHz): Result:(-19.5 dBFS, 5.00 MHz) - PASSED
->RF Loopback Test PASSED
=> Board tests PASSED <=
Elapsed time: 2.66 seconds
I was able to get rid of the error eventually by stepping through TX gain values. However the FFTViewer results still give me a bad feeling I’ll run into power issues down the road in regards to TX/RX so any advice is still appreciated.
What is your TX local oscillator frequency? I had exact same problem but only for frquencyes bellow 30MHz. Also, for 15.36MS/s samplerate 16384 is too short buffer which will generate too many IRQ for CPU.
TX LO is 1240MHz, however at this point I’ve solved the problem by updating firmware and as previously stated, stepping through TX gain. I’ve acquired an amplifier for any TX power issues I may come across in the future.
