Rohde&Schwarz Oscilloscope behaviour

[Baltazar]

I got an RTA4004 this week.

Amongst others, reviews on this forum (mostly RTM3000) greatly helped me make my choice and I don't regret it.

First two questions, perhaps Rich@RohdeScopesUSA can help:

- How comes that horizontal scale goes in 1-2-5 steps everywhere except at 40ns/div and 80ns/div where I would expect 50 & 100ns/div?

- When I power up the scope with a signal connected while observing this same signal on another scope, I see that signal amplitude is pulled lower for some time during startup. Maybe the 50Ohm termination is activated temporarily. This can be dangerous, possibly causing damage to the scope. Couldn't this be avoided? The other scope (HMO2024) doesn't do that.

[Hydron]

I think the 40 and 80 ns/div thing is to get an integer pixel:sample ratio at these steps for a crisper display. Dave actually made a topic about it here: https://www.eevblog.com/forum/testgear/rohde-schwarz-rtb2004-timebase-quirk/ (and got an answer from Rich)

As for the power up thing, maybe check with a multimeter to see if it does drop to 50R during startup? Do you hear a relay click?

[Baltazar]

Thanks for the link. While it sounds like a reasonable explanation, I see no real difference in image quality between 40/50 and 80/100 ns/div, neither om my scope nor in the picture in the related thread.

I checked with a DMM, the input impedance is indeed 50Ohms for some seconds during startup. This is not appreciated. I must remember to be careful and hope this will be avoided in next FW release.

[2N3055]

This made me curious, so I checked my Keysight MSOX3000T to see how it behaves.

When set to 1MOhm, when off,  it actually disconnects input, and keeps it off (high impedance) until scope initializes.
Then it switches in input atten and drops to 1 MOhm.

But, if you enable 50 OHm, and switch off the scope, it also disconnects internal electronics, but it KEEPS 50 Ohm terminator switched in. Scope stays 50 Ohm terminated even when OFF.  All the time. I guess they used bistable relay for 50 Ohm termination.

So if you keep scope at 1MOhm, it will completely disconnect inputs when off, but if you were working with 50 Ohm before switch off, input will stay at 50 Ohm even when scope is off.