Thank you,
I disabled the CMIX in the RxNCO , and then ran the “caliberate Rx“
Note that running “caliberate Rx” automatically enables the RxNCO DC corrector and DC tracking loop and it is observed that the spike is at 0Hz at a level of approx -70dBFS which is same at the same level as “digital processing artifact” which was created earlier when the mixing with NCO occured
this is was a little surprising as I expected to see the spike at 0Hz to drop to around -95dBFS like the shifted DC did when I used the RxNCO where the “Caliberate Rx” was done and the DC corrector and DC tracking loop of the RxTSP were not bypassed.
pls see the below image:
This got me thinking that what you described as a “digital processing artifact” occurring due to mixing with the NCO might also be happening when the DC corrector and DC tracking loop are enabled. Digital DC corrections may also be causing the single bit offset.
The DC spike at 0Hz appears to be at the same level whether the NCO is enabled or disabled (in both cases, “Calibrate Rx” was performed and the DC corrector and DC tracking loop were kept enabled). Pls let me know your opinion on this.
now if I bypass the DC corrector and DC tracking loop, to remove any digital correction and only observe the analog correction, the spike at 0Hz becomes taller to approximately - 62 dBFS
I was also going through TX DC calibration not working - #2 by ricardas
and this chat gave the idea to tweek 0x05C8 DC_RXAQ and 0X05C7 DCRXAI registers, through that I was able to reduce the spike at DC to abt -80 dBFS
with the 0x05C8 DC_RXAQ and 0X05C7 DCRXAI values as shown below:
However, I observed that these DC correction values vary across different LimeSDR Mini 2.4 boards.
I tested the same procedure on another board, and max reduction at 0Hz spike level that I was able obtain after trying all the combination of 0x05C8 (DC_RXAQ) and 0x05C7 (DC_RXAI) register values was approximately –70 to –75 dBFS.
Please clarify,
1. how can I reduce the DC spike to even closer to the noise floor(like USRP) using analog correction methods for DC elimination , any register tweeking technique ?