Oscilloscope bandwidth v time/div

[FreeThinker]

Hi I have an oscilloscope with a 50 mhz bandwidth, its time/div goes down to 2ns so far so good.However I have seen 100mhz scope with a time/div of 2ns and 50mhz scopes with a time/div of 5ns. Ok now i'm confused, I know bw is the 3db roll off but how does this relate to the time base? seems to be arbitrary and manufacturer dependent.Any one any info?

 

[Nigel Goodwin]

It's simply an arbitary decision by the manufacturer - the same applies to Y deflection settings as well, with some scopes having far better ranges than others.

 

[FreeThinker]

Thanks, as I thought.Prolly to do with standard units being cobbled together to a price point.Still don't see why they would have a better band width then horizontal resolution unless it's a transient thing.

 

[crutschow]

It costs more to have an accurate, fast time-base sweep for an analog scope, so cheaper scopes generally have a slower maximum sweep rate.

Cost is not much of a factor for digital scopes since the physical horizontal sweep rate is unrelated to the displayed time base at small time/div display. The digital sampling system collects the data rapidly, stores it, and then displays it leisurely on the display. That's why high speed data can be displayed on a slow LCD screen.