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| Best Brand Name for an Oscilloscope? |
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| MrAl:
--- Quote from: pdenisowski on December 02, 2022, 02:32:14 pm --- --- Quote from: MrAl on December 02, 2022, 02:09:29 pm ---Yes that is the way i have been doing it, sweeping a sine was up in frequency until you see the amplitude drop to 1/sqrt(2) which is the -3db point. Since to do this test for a higher frequency scope like 100MHz you have to have a signal generator that can produce sine waves up to at least 100MHz. --- End quote --- Yes, this is how I measure oscilloscope bandwidth, although I realize that most hobbyists don't have signal generators that go up to the GHz range :) If I were going to to a video on this topic ("Understanding Oscilloscope Bandwidth Measurements" or similar), I would want to include approaches that don't require (very) high frequency generators. I also think it's helpful to measure beyond the nominal 3dB bandwidth in order to graph out the frequency response (Gaussian, flat, something in between). As some others have commented, a scope is sometimes useful (well) past its 3dB bandwidth -- such as when measuring a reasonably pure sinusoid -- as long as you take the decrease in level accuracy into consideration. This also requires graphing the frequency response past the 3 dB point. Another reason to graph this out is that the frequency response may have (non-trivial) ripples or other irregularities even within the 3 dB bandwidth. One advantage of scopes with a Gaussian frequency response is that they tend to have lower passband distortion than a flat / brick wall response. --- End quote --- Yes it's too bad getting a hold of a very high frequency generator is not that cheap, and i am not sure i want to shell out for one just to be able to tests scopes. I have a PC board that goes up to 40MHz but i'd have to dig it out and hook it up to a microcontroller to get it going again. If you have a really really good scope around you may be able to offer a small service to members. Measure the rise time of one of their oscillators and hand them that spec. They can use that to get some idea how their scope is behaving. I think it's important to know the rise time though and if the actual wave front was graphed, that would be even better. Using maybe a 20 point algorithm the bandwidth could be estimated. I see that some are saying that digital scopes are not that simple though so not sure if this would work for every scope out there, just the ones with an equivalent first order low pass filter front end. I think a square wave test tells us a lot of information even if it is lower frequency because the harmonics present go way up there if the rise and fall times are sharp. I can transmit a 100k square wave modulated signal to a radio at 7MHz or something like that so the harmonics are reaching up pretty high there. Maybe i should look into this more. I know a square wave gets very curvy as the higher frequencies get more attenuated, but i dont think it helps unless we know the slope of the rise and fall times. |
| Vachik:
--- Quote from: tautech on December 01, 2022, 03:00:32 am ---I'd never seen the likes of rated BW exceeded by 85% in any instrument. --- End quote --- R&S RTC1002 with the 100 MHz option enabled has a bandwidth of 200+ MHz. According to my estimates, about 250 MHz. |
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