I have rebuilt this X2 multiplier using ground plane methods and things look a lot better. I am not using probes. I am taking the output as a sine sine wave at 10dBm from my sig gen direct to the multiplier using BNC terminated 50 Ohm coax, and the multiplier now has proper BNC sockets for input and output. Similarly I am taking the X2 square wave output from the X2 multiplier direct to my old Tektronix 7854 scope with BNC terminated coax. I am using a T piece at the scope end with a 50 Ohm termination BNC resistor. Whilst I am told this will now be fine to run the rest of my project I am curious as to why part of the square wave is rounded off.
I also took the 136kHz output from the sig gen direct to the scope, again terminated in 50 Ohm, but as a square wave. I see rounding on two sides of the square wave like that. Temporarily I have to have the scope and sig gen, which is rack mounted, some distance apart so am using maybe 12 feet of coax in total, in and out of the multiplier. I think this may be the cause. Comments welcome, thanks.
Alan, your video was very useful! Thank you for such helpful YouTube posting.