Strong Spike at 0 Hz

#1

Hi All,
I have a Lime mini connected at the USB3 port.
I am using the latest firmware, gateware and LIMESUITE GUI.
After connecting to the board I did:
Press Default
SXR Tab- Set Frequency- 70.000 MHz - Press Calculate- Press Tune
RBB Tab- Set Rx Filters- Rx Bandwidth=3 MHz
RFE Tab- Active Path to RXFE=LNAW
Calibrations Tab- Automatic DC Calibration Mode- Calibrate RX

After activation the FFT window,I get is a strong spike at -73 dbFS at 0 Hz.

Is checking the Automatic DC Calibration Mode not enough for DC Removal?

#2

That’s to be expected - it’s often called “zero bang”, and it results from there being a DC offset in the signal. It’s damn difficult to completely remove it, which is why most systems will try to avoid using that part of the spectrum. You may be able to reduce it if you haven’t switched in the DC offset logic in the part, but you won’t be able to make it completely go away. -73dBFS is a very small amount of DC.

#3

I am aware of the DC Offset, but there is no signal at the input and I was hoping that LIMESDR Mini removes the DC Offset possibly generated by the Zero-IF architecture.
There must be a setting I am missing.