@gunrunnerjohn posted:OK, I"m suitably jealous.
What differential probe are you using? ...
For most if not all train stuff looking at differential signals, I use a 2-channel DIY differential probe - $0 out-of-pocket using parts from the stash. I see I fabricated a PCB for it but this was sometime in the last century so I'm sure the documentation is in the bit bucket. But it's just a dual-channel op-amp configured with 10x scale-down so as to be compatible with a scope 10x probe setting for properly scaled on-screen parameter measurements. The other reason for a 10x scale down is to get a common-mode voltage range to allow the same scope to probe O-gauge track voltages with its "ground" (outer-rail) and the circuit board signals after a bridge rectifier with its "ground." Only a few MHz bandwidth but even for, say, the signals shown above - 25 kHz PWM motor drive - a 1 MHz bandwidth probe is 40 times the pulse rate which is adequate for seeing what's going on.
I can't off the top of my head think of a train application where I needed a high-speed (i.e., >100 MHz bandwidth) differential probe. Those probes are VERY spendy - no doubt more than the cost of a Regal scope.
