Nice job on reverse engineering this.
Thanks
I can only guess at all of this though because I don't have access to the hardware. So there are bound to be mistakes.
Here's an updated block diagram although this block diagram still doesn't explain the very low phase noise on the 100MHz trace on Rigol's datasheet. So something still isn't right somewhere.
But the 5 bands shown in my block diagram agree with the 5 frequency bands shown in their datasheet in terms of frequency range and divsion ratio.
Did anyone noticed the 3 LED looking diodes in the VCO section? (D200, D205, D210)
Presumably these wink on and off as each VCO gets selected. This would help an engineer during the dev phase.
The transistor used for the VCO appears to be an Infineon part = BFP450. I have a non linear model for this part here and I simulated the VCO layout for each range using this part. I adjusted the C-E capacitor for best negative resistance and the little printed resonator and the two series varactor diodes do seem to deliver the required oscillation frequency to cover about 1800MHz to 3600MHz in three ranges if I use typical capacitance values for this type of VCO tuning diode.
I'm estimating that the 50 ohm traces are about 0.04" wide and the outer RF layer is somewhere around 0.02" thick with a dielectric constant around 4 to 4.3.
The elliptic lowpass filter marked as 3000MHz in my block diagram does seem to cut off at just over 3GHz if I simulate it in Sonnet using the PCB data above.
This (and the VCO resonator dimensions) does suggest that this hardware is designed to cover up to a 3GHz frequency range.
So maybe the 1.5GHz version is just crippled in firmware? So maybe it can be hacked to become the 3GHz version?