spur!!!amplifier when input 192MHz bandwidth QAM256 signal.

When input 192MHz bandwidth QAM256 signal, there is some spur frmo 40MHz to 120MHz. The input signal frequency is 189~381MHz,32channel, power level is -39dBm per channel. The amplifier is ACA2407. Why?

Thanks!

Since spur 2 is 2/3 the frequency of spur 3, that would suggest where they are coming from. What do you have in the system that is running at ~256 MHz?

Also, why is there a huge spectral drop-out around 280 MHz? Is that your LO frequency? Why is there a drop-out at 280 but not 256?

As far as the other spurs (lower frequency), well you have all sorts of intermod products. They can easily generate the spurs seen. What happens the the low frequency spectrum( in dBc) if you put a 10 dB pad before the amplifier?

Thanks biff44
The spur 2 and 3 is coming from clock, which is 512MHz.

Those spur form 40MHz to 120MHz may be produced by 2 order nonlinearity. But the output power is far away less than P1dB of ACA2407. The P1dB may be 24dBm.

When using SBB-5089 which P1dB is about 19dBm, the power level of those low frequency spur is less than it of ACA2407.

Why?

That huge spectra drop out is because that the input signal include 2×16 channels QAM signal. There is a 6 MHz gap between each 16 channels. So that is not a problem.