## Bandwidth and maximum frequency

Which product is right for your exact requirements
nutron
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### Bandwidth and maximum frequency

Hi.
i am looking at the 3205D scope and in its specs it says that it has a bandwidth of 100MHz.

When you guys say 100MHz bandwidth , does that mean that one can capture a 100MHz square wave mostly accurately with a 3dB amplitude drop or does one have to de-rate the maximum possible frequency one can accurately capture by 3 ?

Martyn
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Joined: Fri Jun 10, 2011 8:15 am
Location: St. Neots

### Re: Bandwidth and maximum frequency

Bandwidth is for a sine wave with 3dB drop.
Martyn
Technical Support Manager

nutron
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### Re: Bandwidth and maximum frequency

so how far can one push the frequency of other non sine wave forms before they start losing their shape. lets take a square wave as example.

Martyn
Posts: 3864
Joined: Fri Jun 10, 2011 8:15 am
Location: St. Neots

### Re: Bandwidth and maximum frequency

If you consider that a square wave consists of the sum of sine waves of odd harmonics at diminishing levels, you need at least the fundamental, third and fifth harmonics to generate a basic square wave appearance.

So divide the bandwidth by 5, and a 100MHz bandwidth will give a reasonable representation of a 20MHz square wave.
Martyn
Technical Support Manager

nutron
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Posts: 4
Joined: Sun Jul 07, 2019 3:37 am

### Re: Bandwidth and maximum frequency

Please help me to understand something here , i am fairly new to picking a scope by spec.

What i know about sampling analog signals to digital is that the maximum frequency that can be sampled is half of the sampling frequency when the waveform frequency is constant , like a static sine wave (Nyquist) .
I also know that sampling analog signals right at the Nyquist frequency is not a good idea either.
So i assume you rate the maximum bandwidth of your products bellow the Nyquist frequency.

When i look at this website : 3000 series specs

Let's pick a 100Mhz bandwidth version of this series.
Looking at the "Oscilloscope - Horizontal" section it says that using the scope with one channel the sampling rate is 1Gs/s and with two channels it is 500Ms/s etc.. .

So at 1 Gs/s the Nyquist frequency is 500MHz and at 500Ms/s the Nyquist frequency is 250MHz etc... .

Does that mean this for the different channel configurations of the 100MHz bandwidth version?
1 channel : 1Gs/s , Nyquist freq. 500MHz ,max bandwidth 100MHz ,5 samples per period at 100MHz signal
2 channels : 500Ms/s , Nyquist freq. 250MHz ,max bandwidth 50MHz ,5 samples per period at 50MHz signal
4 channels : 250Ms/s , Nyquist freq. 125MHz ,max bandwidth 25MHz ,5 samples per period at 25MHz signal

If that is the case , would that mean that the 200MHz version of this scope will be less accurate at the maximum bandwidth frequencies of each channel configuration , since the sampling rate is the same for all versions of the 3000 series?
Like this...

1 channel : 1Gs/s , Nyquist freq. 500MHz ,max bandwidth 200MHz ,2.5 samples per period at 200MHz signal
2 channels : 500Ms/s , Nyquist freq. 250MHz ,max bandwidth 100MHz ,2.5 samples per period at 100MHz signal
4 channels : 250Ms/s , Nyquist freq. 125MHz ,max bandwidth 50MHz ,2.5 samples per period at 25MHz signal

Please correct me if i am wrong , I am not certain if am right with all of this. As i said i am new to picking scopes by specs and i would really appreciate some help to understand the specs of a scope.

nutron
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Joined: Sun Jul 07, 2019 3:37 am

Bump.

Martyn