Read the top line on your first screenshot:
5 Ms/s
So, that's good till 2.5MHz, that is to say meaningless (a minor miracle something vaguely resembling the real signal is shown at all)
Read the top line on your first screenshot:
5 Ms/s
So, that's good till 2.5MHz, that is to say meaningless (a minor miracle something vaguely resembling the real signal is shown at all)
If there's no modulation, then not necessarily - it is ultimately limited by the analogue front end.
To put it simply, if I have a 1MHz bandwidth signal on a 1GHz carrier, then I only need to sample at >2MS/s. However, the sampling head has to have useful behaviour at 1GHz.
Read the top line on your first screenshot:
5 Ms/s
So, that's good till 2.5MHz, that is to say meaningless (a minor miracle something vaguely resembling the real signal is shown at all)
If there's no modulation, then not necessarily - it is ultimately limited by the analogue front end.
To put it simply, if I have a 1MHz bandwidth signal on a 1GHz carrier, then I only need to sample at >2MS/s. However, the sampling head has to have useful behaviour at 1GHz.On paper, yes, no doubts about it, and that's, in fact the principle ETS DSO are based upon, if I'm not mistaken:
if the signal is repetitive, and band limited you can under sample it and obtain a correct reconstruction.
But here we have a signal that varies in time and I can expect the result to depend on interference between the signal period, the waveform update rate and the scan blind time.
So I would not trust this kind of results.
QuoteBut here we have a signal that varies in time and I can expect the result to depend on interference between the signal period, the waveform update rate and the scan blind time.
So I would not trust this kind of results.
Quite possibly, but not necessarily. I would want to play with the scope and signal before deciding what's happening.
ng of the sampled signal.
(Admittedly, I was a bit too dry in the first post. I should not answer when I'm >50% asleep... )
Read the top line on your first screenshot:
5 Ms/s
So, that's good till 2.5MHz, that is to say meaningless (a minor miracle something vaguely resembling the real signal is shown at all)
If there's no modulation, then not necessarily - it is ultimately limited by the analogue front end.
To put it simply, if I have a 1MHz bandwidth signal on a 1GHz carrier, then I only need to sample at >2MS/s. However, the sampling head has to have useful behaviour at 1GHz.On paper, yes, no doubts about it, and that's, in fact the principle ETS DSO are based upon, if I'm not mistaken:
if the signal is repetitive, and band limited you can under sample it and obtain a correct reconstruction.
But here we have a signal that varies in time and I can expect the result to depend on interference between the signal
period, the waveform update rate and the scan blind time.
So I would not trust this kind of results.
Am I completely off-track? I admit my digital signal theory is a bit rusty, to say the least, so thanks for any clarification.
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People have checked the frequency response of their DS1054Z's "retro-style" using a series of "spot " frequencies,without the result looking anything like the OP's screenshot.
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People have checked the frequency response of their DS1054Z's "retro-style" using a series of "spot " frequencies,without the result looking anything like the OP's screenshot.
I think it's important to get this into the thread lest newcomers see the traces and just assume the problem is with the scope.
but had not noticed the scope was not saving screen grabs.
[
People have checked the frequency response of their DS1054Z's "retro-style" using a series of "spot " frequencies,without the result looking anything like the OP's screenshot.
I think it's important to get this into the thread lest newcomers see the traces and just assume the problem is with the scope.
Well, the problem is with the scope, but it doesn't mean the scope is at fault! Such issues can occur with any measuring instrument, if its operation and limitations aren't understood.
(In general I don't think it is fair to punt the issue and say the "problem is with the operator" - although sometimes that is the inescapable deduction!)
I have access to a leveled sweep signal generator so I hooked it up to my Rigol DS1054Z sweeping 0 to 200 MHz.
What would be a good setup for this and are there any other interesting measurements I can make using the sig gen?
And where did the modulation term come from?
I must be missing something. There is nothing in the discussion that makes me believe it is a scope problem. But then there is the issue of 'confirmation bias'. Maybe I really did miss something!
[
People have checked the frequency response of their DS1054Z's "retro-style" using a series of "spot " frequencies,without the result looking anything like the OP's screenshot.
I think it's important to get this into the thread lest newcomers see the traces and just assume the problem is with the scope.
Well, the problem is with the scope, but it doesn't mean the scope is at fault! Such issues can occur with any measuring instrument, if its operation and limitations aren't understood.
(In general I don't think it is fair to punt the issue and say the "problem is with the operator" - although sometimes that is the inescapable deduction!)
I thought the issue reduced to something bizarre with the signal generator. Is that not the case?
We know full well that the scope doesn't roll off to -3dB until somewhere around 150 MHz. This has been documented and there's a video out there somewhere. If I had a signal generator, I would simply duplicate the test using a simple sine wave and varying the frequency.
I was pretty careful to avoid the term 'operator error'. I have no idea why the display is showing what it is except that I am not quite ready to throw the scope under the bus given that the signal wasn't even terminated. And where did the modulation term come from?
I must be missing something. There is nothing in the discussion that makes me believe it is a scope problem. But then there is the issue of 'confirmation bias'. Maybe I really did miss something!