I am just starting to learn how to use the AD9361, and I seem to be having some issues getting a nice clean CW signal. The tuner is installed on a custom board, with signal samples fed to an FPGA, then to a DSP for capture. I pull out the samples then analyze in MATLAB. These are the initialization parameters, sampling characteristics, and input signal parameters I am using:
- 26 MHz VCTCXO input
- 30.72 MHz sampling
- LO 900 MHz in one case, and 2147 MHz in another
- CW inject at 901 MHz in one case, and 2148 MHz in another, from -65 dBm down to -95 dBm
- with Rx FIR (filter coefficients unchanged from those specified in the default_init_param object in the ad9361 lib), and without Rx FIR (both scenarios seems about the same)
- I have inspected the DC power inputs with a scope at the chip and see no AC signals which might be mixing in.
- I have inspected the 26 MHz VCTCXO input with a SpecA at the chip and see no harmonics which might be mixing in.
- I have inspected the RF signal input with a SpecA at the chip, and it looks clean.
- I have ensured no data corruption in the AD9361/FPGA/DSP signal path by putting the AD9361 in BIST mode, generating a tone, and inspecting the samples in MATLAB.
Below are some MATLAB figures showing the time series and spectrum. I am trying to understand what might be causing the signal to become so dirty. Many thanks in advance!