It's possible (hopefully not!) that the manufacturer of this instrument has assigned a different meaning to the term bandwidth. The old TEKTRONIX scope is considered to have a 200 MHz bandwidth when a 200 MHz sinusoid is reduced 3 db in amplitude.

What you describe suggests that this instrument does, indeed, have a wider bandwidth than the 3 MHz that's been mentioned here and there. Do you have a signal source that can produce a sine wave at frequencies in the 5-15 MHz range? What would be interesting, too, would be one such generator for each of the four channels, just to see how it displays different sgnals at precisely the same frequency, but in different phase, as well as how it displays four signals at slightly different frequencies.

None of these investigations are intended to malign your new instrument, but, rather, to point out the abilities and limitations, particularly in the context of what you might see, as an indication that it's time to get out the old analog 'scope.

Commercially available signal sources seem to be getting harder and harder to buy, these days, first because they are often limited in both frequency and amplitude, and because they seldom have the features to which I, as an old-timer, have become accustomed. You can obtain a pretty good DDS generator today, but the really complete and really "good" ones are quite expensive. They should allow you to drive at least a 50-ohm load, as that's standard, and swing 15-20 volts to either side of common when terminated into 50 ohms. I have had generators of that class for decades, and certainly rely on them. Arbitrary waveform generators are pretty useful, too, as you then don't have to build application-specific circuitry. Back in the '70's, I became enamored of the TEKTRONIX TM5000-series of instruments. These are like the older TM500-series but are most often MCU controlled and GPIB-capable. As a consequence, I often, incorrectly, assume that anyone working in a serious lab facility has such equipment at his disposal. Both the TM500 and TM5000 series are mainframe-based, i.e. they rely on a power chassis into which the various instruments are plugged as modules. Even the old FG504 signal generator was capable of wide voltage swing over the range from DC to 40 MHz with sweep capability, phase-locked loop, amplitude and frequency modulation, external trigger, and numerous other features that I don't use frequently. I do use the adjustable rise and fall time, duty cycle, and other adjustments frequently, however, and they'd be really handy in "checking out" your new 'scope.

These things were once VERY expensive, but are now not so costly, and, with a little study, can be locally adjusted and maintained. Both series had counters, generators, power supplies, 'scopes, DVM's, arbitrary waveform generators, and lots of other functions. The only problem, and I'd caution you about that, is that it's very hard to find anyone smart enough to repair one if it is broken in some way. The circuits often use matched transistors or diodes, and those are not so easy to replace. My main hassle has been that the 40-year-old electrolytic cap's are gradually in need of replacement.

You might find that exercising your 'scope with 20 ns rather than 200 ns variation in frequency will show you things that later prove valuable, as the 'scope may not show the 20 ns difference reliably. You will learn to recognize the symptom, though, and then will simply switch to the analog instrument.

Good luck!

RE