General > General Technical Chat
Frequency Divider for older Oscilloscopes??
Jorge Ginsberg:
--- Quote from: 2N3055 on July 18, 2021, 09:30:19 am ---
--- Quote from: Jorge Ginsberg on July 18, 2021, 09:10:05 am ---
--- Quote --- what you want is not possible. You have to have 100MHz bandwidth scope, no matter if it is analog, analog sampling, digital sampling or digital real time.
So, yes, you need to get a 100MHz scope to have a 100MHz scope.
You could use current low bandwidth scope as a display for sampling head (that other already pointed to).
Problem is that ANY 100 MHz scope (even the most stupid ones, that you can get for 100 USD new) will be better than any contraption you can make cheaply...
Sorry.
--- End quote ---
2N3055 : You are wrong. (nice nickname)
It is perfectly possible to make a circuit that takes samples of the 100 MHz signal and with those samples make an exact copy but at 10 Khz, so that they can be observed by a cheap oscilloscope.
The problem here is not the technology but the cost.
If China sells you an oscilloscope capable of sampling a signal at a rate of 2 Gs/s, for a ridiculous price of 400 dollars, it is silly to work so hard to make a homemade prescaler that will surely cost more than that.
Just look here and be amazed at the price:
https://www.rigolna.com/products/digital-oscilloscopes/1000z/
But from the technological point of view there is no problem to do it. And I know very well what I'm talking about...
The only justification for such a project is the enthusiasm for electronics and the pleasure of doing it. Nothing more than that.
--- End quote ---
You might know what you're talking about but you didn't seem to understand what I did talk about.
You simply misunderstood. English is not native language for either of us.
Please read again: you cannot look at high frequency signal on a low bandwidth scope with a PRESCALER ( a divider like the one used in frequency counters).
Which was OP original question.
And you can't.
And few sentences later I say " You could use current low bandwidth scope as a display for sampling head (that other already pointed to)."
Which is obviously true because thousands of scopes like that exist...
At which time you're looking at 100 MHz signal with your homemade 100MHz+ sampling scope consisting of a homemade sampling head and a low bandwidth scope used as a display unit for sampler.
At home it is not too hard to make a sampling head that will sample at 1 GS/s (1GHz). But today you can buy cheapest scope that already samples at that rate, and for the price of component to make sampling head (unless you already have the parts). And then you still have only sampler and no input stages, attenuators etc...
And making a 10-20 GHz sampler at home is not that trivial..not to mention 4-8 GHz front end... That one would be useful though..
Regards,
--- End quote ---
OK. It may have been a problem with the language. I don't rule it out. It is true that English is not our native language. I am using "Google translator" to write this.
Let's start over.
There is no need to build a device at home that samples at a rate of 1 or 2 Gs/s. Transforming a 100 Mhz signal into a 10 Khz signal is possible by sampling at the rate of one sample per cycle. That is: if your signal is 100 Mhz, your sampling will also be 100 Mhz. Even your sampling can be slower, as long as you keep the synchronism. And this, is the more critical thing in the design.
It's a pity I didn't save the circuit but I did this more than 30 years ago and I remember perfectly how I did it, the only thing I don't remember is the circuit but any electronics hobbyist could redesign it.
From an economic point of view it is not worth it but if you have fun doing it it is fully justified.
Regards from Argentina
2N3055:
--- Quote from: Jorge Ginsberg on July 18, 2021, 10:21:58 am ---
--- Quote from: 2N3055 on July 18, 2021, 09:30:19 am ---
--- Quote from: Jorge Ginsberg on July 18, 2021, 09:10:05 am ---
--- Quote --- what you want is not possible. You have to have 100MHz bandwidth scope, no matter if it is analog, analog sampling, digital sampling or digital real time.
So, yes, you need to get a 100MHz scope to have a 100MHz scope.
You could use current low bandwidth scope as a display for sampling head (that other already pointed to).
Problem is that ANY 100 MHz scope (even the most stupid ones, that you can get for 100 USD new) will be better than any contraption you can make cheaply...
Sorry.
--- End quote ---
2N3055 : You are wrong. (nice nickname)
It is perfectly possible to make a circuit that takes samples of the 100 MHz signal and with those samples make an exact copy but at 10 Khz, so that they can be observed by a cheap oscilloscope.
The problem here is not the technology but the cost.
If China sells you an oscilloscope capable of sampling a signal at a rate of 2 Gs/s, for a ridiculous price of 400 dollars, it is silly to work so hard to make a homemade prescaler that will surely cost more than that.
Just look here and be amazed at the price:
https://www.rigolna.com/products/digital-oscilloscopes/1000z/
But from the technological point of view there is no problem to do it. And I know very well what I'm talking about...
The only justification for such a project is the enthusiasm for electronics and the pleasure of doing it. Nothing more than that.
--- End quote ---
You might know what you're talking about but you didn't seem to understand what I did talk about.
You simply misunderstood. English is not native language for either of us.
Please read again: you cannot look at high frequency signal on a low bandwidth scope with a PRESCALER ( a divider like the one used in frequency counters).
Which was OP original question.
And you can't.
And few sentences later I say " You could use current low bandwidth scope as a display for sampling head (that other already pointed to)."
Which is obviously true because thousands of scopes like that exist...
At which time you're looking at 100 MHz signal with your homemade 100MHz+ sampling scope consisting of a homemade sampling head and a low bandwidth scope used as a display unit for sampler.
At home it is not too hard to make a sampling head that will sample at 1 GS/s (1GHz). But today you can buy cheapest scope that already samples at that rate, and for the price of component to make sampling head (unless you already have the parts). And then you still have only sampler and no input stages, attenuators etc...
And making a 10-20 GHz sampler at home is not that trivial..not to mention 4-8 GHz front end... That one would be useful though..
Regards,
--- End quote ---
OK. It may have been a problem with the language. I don't rule it out. It is true that English is not our native language. I am using "Google translator" to write this.
Let's start over.
There is no need to build a device at home that samples at a rate of 1 or 2 Gs/s. Transforming a 100 Mhz signal into a 10 Khz signal is possible by sampling at the rate of one sample per cycle. That is: if your signal is 100 Mhz, your sampling will also be 100 Mhz. Even your sampling can be slower, as long as you keep the synchronism. And this, is the more critical thing in the design.
It's a pity I didn't save the circuit but I did this more than 30 years ago and I remember perfectly how I did it, the only thing I don't remember is the circuit but any electronics hobbyist could redesign it.
From an economic point of view it is not worth it but if you have fun doing it it is fully justified.
Regards from Argentina
--- End quote ---
Yes, Jorge, you are correct. That technique is how sampler scope works. It has sample and hold circuit that takes quick ( 1 nsec) sample of signal at input at precise moment. And plots it on output device. Than it takes sample at different time. And plots that. And if you do this 1000 times, you will have reconstructed input signal. You can do that sequentialy (equivalent time sampling) or randomly and measure time (random interleaved sampling, RIS). That is how sampling scopes work. It doesn't have to be one sample per period, it can be much less. You can literally plot on a paper plotter, as long as input signal is repetitive and newer changes. And that is problem with analog sampling scopes, they work only for repetitive signals or for eye diagrams....
Best regards,
bdunham7:
--- Quote from: 2N3055 on July 18, 2021, 02:59:42 pm ---Yes, Jorge, you are correct. That technique is how sampler scope works. It has sample and hold circuit that takes quick ( 1 nsec) sample of signal at input at precise moment.
--- End quote ---
I think the method he is talking about is slightly different. Instead of storing and plotting the samples to reconstruct the original waveform, I believe what he describes simply samples the waveform at a slightly different frequency than the input signal (or possibly a harmonic or subharmonic frequency) and then renders that to the screen in real time. The effect is that the original signal is aliased down to the difference, or something like that--so the scope is actually displaying a much lower frequency signal that is hopefully correlated with the input signal in a known manner. Maybe you could call that a sampling downmixer? Although it can be demonstrated for known signals, I don't think it works too well in the general case.
Jorge Ginsberg:
No bdunham7. That is not what I am trying to say. "2N3055" has understood me better what I am trying to say.
What I am saying is that it is possible to take copies of a 100 Mhz signal (to give an example) and display them at a much lower frequency, so that they can be viewed on an inexpensive low bandwidth oscilloscope.
If you take a single sample per period and repeat the same thing for 10,000 periods, when you reconstitute the signal, it will be an exact copy of the original signal, but its frequency will be 10,000 times lower. By doing that it is possible to observe a 100 Mhz signal as if it were a 10 Khz signal, something that any cheap oscilloscope can do.
And it is not difficult to achieve. The only thing necessary is to have elements that work properly in the UHF band. I did it with BFY90, MPF102, BF960 transistors and and some TTL-Shotky flip-flops. And the resistors should be non-helical so they have almost no inductances.
And I could see UHF signals on a simple Telequipment D61 oscilloscope.
And I think that's what GlennSprigg is looking for , only that when he made his first query he expressed himself badly because he mentioned a "prescaler" which is used only to measure frequencies and not to observe waveforms, although if we go by the concept of the term "prescaler", what we are doing on the oscilloscope is conceptually something similar: moving to the low frequency domain something we can't observe or measure in the high frequency domain.
Jorge Ginsberg:
Yes "2N3055". Finally we agree.
Note that even if a 100 MHz signal does not keep its shape all the time and has variations from time to time, even so, thousands of periods are still repetitive.
For example, suppose a 100 MHz signal has a change of shape every thousandth of a second, yet, between one change and the next, there are 100,000 identical periods between one change and the next. And those 100,000 different periods can be sampled.
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