One of the ways you can estimate the frequency response (-3 dB Bandwidth = BW) of a DSO, is to measure the rise time or a very fast rise time pulse and use the formula:
BW ~= 350/Tr
where Tr is the measured rise time of the pulse.
So we would expect the rise time of the DS2 series to be:
Scope BW MHz ~Rise Time
DS2072 70 5.0ns
DS2102 100 3.5ns
DS2202 200 1.75ns
The rise time of the test pulse should be less than 20% of the Tr of the scope to create less than about 2% error. The problem for many, is where to find an appropriately fast rise pulse to apply to the oscilloscope.
The relatively slow rise time calibrator pulse, which is only intended to calibrate amplitude, is entirely unsuitable for Tr measurements. Fortunately, the Rigol DS Series has a trigger out pulse available on the rear panel that can serve moderately well if you do not have access to something faster.
Lets look at it.
To minimize the cable reflections, the 42" 50 ohm good commercial coaxial cable transferring the pulse to the measuring scope was terminated with a good quality 50 ohm feedthru, like the Rigol PL-50, if the scope does not have a 50 ohm input option - like the Rigol DS Series.
My measurements of the trigger out pulse were done on a 1990s vintage, but still very functional, Tektronix 7904A using a Tr=25ps (0.025ns) type S-4 head in a 7S12 sampling plugin (photo 1). It's accuracy was affirmed by measuring a Tektronix S-2 25 ps pulse generator head correctly. A BNC to SMA adapter and 10dB attenuator was used at the sampling head to reduce the DS2202's trigger voltage.
Since it is an analog scope, we have to do some things the old fashion way. The input signal is set to be 5 divisions high and the time to transverse the center 4 vertical divisions (10% to 90%) is the rise time. The accompanying photo shows this is 1.0ns (photo 2) through the 42" BNC cable. A 50 ohm feedthru is not necessary, as the input impedance of the sampling head is 50 ohms.
An additional measurement using a military quality 9" BNC cable gave 0.9ns for the pulse rise time - but that cable is too short to reach from the rear output to the DS scope's input.
So there we have it - a readily available moderately fast rise time pulse for Rigol DS Series users. It would be much better if it were, say 0.3ns, but we will see there is a way to compensate for it and calculate the true rise time of a scope with a bandwidth into the 200 MHz region.
Measuring a scope's BW using risetime, in my opinion, is not the best way. But scopes measure pulses as well as sine waves, so knowing your scope's risetime is a very good thing.