On 18/10/2024 11:35, je.amg...@gmail.com wrote:
Hello,
I am currently facing an issue with ADC saturation on a USRP X310
equipped with a UBX daughterboard. We are conducting measurements
using an LTE signal and a sinusoidal input signal, but it seems that
the ADC is saturating, leading to a loss of dynamic range in our
measurements.
Test context:
We are transmitting (using a generator) an LTE signal with a power of
-50 dBm at a center frequency of 1815 MHz. Then, we add a sinusoidal
signal at 1865 MHz with a power of -30 dBm. This second, more powerful
signal seems to be causing the ADC to saturate, even though we don’t
see it directly in the IQ samples due to the digital filtering applied
downstream.
Problem:
We suspect that the ADC saturation occurs before IQ conversion and is
therefore masked by the digital filters. This results in a loss of
dynamic range in our measurements, and we feel that adjusting the gain
based on the IQ samples may not be reliable.
Question:
How can this ADC saturation be detected upstream of the IQ processing?
Are there tools or methods to directly monitor the sample values at
the output of the ADC in the USRP (before digital filtering) to
prevent saturation?
Do you have any advice for implementing an automatic gain controller
(AGC) based on reliable saturation indicators?
We would appreciate any suggestions or experiences in resolving this
issue. If you have encountered a similar problem or have ideas on how
to address it, we would be happy to hear your recommendations.
Thank you very much for your help!
A -30dBm signal applied at the antenna inputs, and then amplified
greatly by the amplifier/mixer/gain-chain ahead of the ADC
would very-likely saturate the ADC. A -30dBm signal from an "over
the air" antenna is one that is thunderingly loud in
the real world. It would not surprise me to find that gain elements
ahead of the ADC are *also* becoming non-linear.
Turn your gain down.
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