properly debug limesdr usb and limesdr mini clocking requirements and osmo-trx support
limesdr usb and limesdr mini need a external reference clock to be used for gsm applications properly since the internal oscillator is sadly not of the required performance class.
limesdr usb has an extra internal pll (ADF4002 and Si5351C as well as LMK00105) and can handle different external clocks quite flexible
limesdr mini has no pll chip, but only a clock buffer (LMK00105) and needed some help from the fpga to make clocks possible which are not 40MHz
- File lms_mini_clock_in.png lms_mini_clock_in.png added
- File lms_mini_clock_in_50ohm.png lms_mini_clock_in_50ohm.png added
- File lms_mini_clock_out.png lms_mini_clock_out.png added
- File lms_mini_clock_out_50ohm.png lms_mini_clock_out_50ohm.png added
- % Done changed from 0 to 10
looking at the schematic, i think there should be proper termination for 50Ohm, but i see a lot of ringing on the input which i do not see not there when i only connect the gpsdo to a 50ohm terminated scope input.
the screenshots for the input are done with a bnc-t inbetween the gpsdo and the mini, the output ones are directly connected to the mini.
- % Done changed from 10 to 20
i repeated the experiments today with a 'clock converter' based on ltc6957-4 with 40MHz, still usin limesuite 18.10.
sadly i could not get the dcs1800 band to have better results than with the 10MHz square clock from the gpsdo last time.
next experiment is to use a clock generator based on si5351c