I measured the CH1 RL with a professional VNA and got this values:
100MHz 36dB
300MHz 28dB
500MHz 23dB
700MHz 20dB
900MHz 17dB
Measuring UHF filters would benefit from having a better termination impedance.
I tried to understand the CH1 input attenuator but i don't find any explanation to that topology. Using the SA612 input as single-ended, connecting IN_B to ground through a capacitor as indicated in the datasheet and simplifying the attenuator to a PI or just L arrangement could lead to a better RL with same loss. But i'm sure i'm missing something, as VNWA3 uses the same circuit although with different resistor values. It's input match is much better BTW. Maybe SA612 noise?
Carlos
