I really am keen to try this but I am not sure I have the courage. Can you do it to a single channel? Or is is all or none?
This is an all or nothing mod and if you aren't sure please don't risk your scope.
SNIP
And, as is made clear by the mod, the whole backend of the scope is capable to 1 GHz (or higher )
SNIP
Is that a challenge?
I know the front end ASIC is capable of at least 1.5 GHz as it is used in the 4000x series. My dream was a 1.5 GHz upgrade but without seeing a 4000 series 1.5 GHz front end it just isn't going to happen. It was hard enough to determine the required values for 1 GHz.
There is the jumper option on the board for 1.5 GHz but as far as I am aware it will be rejected as it isn't a 4000 series board. I have no desire to get into firmware hacking.
I don't need to sleep, I'll be pondering it.
Would this part of the mod be worth doing just on its own, for a 200MHz scope, without doing the rest of the mod? Or at 200MHz is it not gaining you so much.
There is nothing to be gained by modifying the 200 MHz front end for a better 50 ohm match. It also wouldn't work properly as the relay/attenuator controls change when you go from 100-500 to 1 GHz hardware.
Can you characterize the response curve? My memory might be bad, but as I recall from the literature, the sub-1GHz models have gaussian response and the 1GHz (as shipped from Keysight) has maximally flat response. Apologies if the posted traces show that fact, I'm a bit excited and haven't read through in detail!
I do believe the 1 GHz model has the flat response. If you look at the anti alias/low pass filter on the output of the front end ASIC you'll see the 1 GHz model has an added series resistor/capacitor. In simulation this prevents attenuation above 500 MHz and changes the curve around 1 GHz.
I will plot the curve when I get a chance.