I am testing 8.185 GHz fixed PLL using HMC703 and HMC509.
The reference frequency is 50.0 MHz. The reference frequency(50.0 MHz) is input from the keysight signal generator.
The power supply uses the DC power supply of the keysight.
Most performance is fine, but spurious is a problem.
The problem is the spurious at + 120Hz and -120Hz from the output frequency.(8.185 GHz)
Especially, the level of the spurious is changed according to the level of the reference frequency.
When the level of the reference frequency becomes higher, the level of the spurious becomes lower.
When the level of the reference frequency is lowered, the level of the spurious becomes higher.
The measurement results are attached. Blue is when the reference frequency is +14 dBm, and black is when the reference frequency is +7 dBm.
I wonder if this unwanted wave can be removed through the loop filter.
If you can not remove it with a loop filter, I wonder how you can remove it.