Author Topic: Frequency Divider for older Oscilloscopes??  (Read 8513 times)

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Offline bdunham7

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Re: Frequency Divider for older Oscilloscopes??
« Reply #50 on: July 19, 2021, 03:26:43 pm »

No, I wouldn't send  you packing. Nothing special about the term "observe", use "see", "visualise", "measure" etc. Yes, all the energy does lie within those bounds; that's the key point :)

True if the signal is repetitive, but for a non-repetitive signal you have to capture it all on the fly (i.e. realtime).

I'm thinking 'observe' might refer to seeing some or all of the characteristics of the signal.  If the energy is truly confined to that bandwidth and you want to capture it sufficiently so as to be able to determine all of the remaining characteristics, I think you need at least 20MSa/s plus at least a small margin to make it practical.  But just a 20MSa/s sampling system isn't all you need--the other stuff necessary would not be trivial, at least for me.
« Last Edit: July 19, 2021, 03:28:37 pm by bdunham7 »
A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 

Offline tggzzz

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Re: Frequency Divider for older Oscilloscopes??
« Reply #51 on: July 19, 2021, 03:49:04 pm »

No, I wouldn't send  you packing. Nothing special about the term "observe", use "see", "visualise", "measure" etc. Yes, all the energy does lie within those bounds; that's the key point :)

True if the signal is repetitive, but for a non-repetitive signal you have to capture it all on the fly (i.e. realtime).

I'm thinking 'observe' might refer to seeing some or all of the characteristics of the signal.  If the energy is truly confined to that bandwidth and you want to capture it sufficiently so as to be able to determine all of the remaining characteristics, I think you need at least 20MSa/s plus at least a small margin to make it practical.  But just a 20MSa/s sampling system isn't all you need--the other stuff necessary would not be trivial, at least for me.

You've got it!

And yes, the sampling aperture does need to be <<1ns, but that is a very small part of the circuit: a pulse, a sampling diode, and a capacitor. High speed scopes typically have nothing else at the front end, and are rather fragile - just like spectrum analysers.

Having said that, one of the few significant advances recently has been the stunning improvement in ADCs and DACs speed and resolution, thus making sampling bridge front ends less important than they were.
« Last Edit: July 19, 2021, 03:53:21 pm by tggzzz »
There are lies, damned lies, statistics - and ADC/DAC specs.
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Offline Jorge Ginsberg

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Re: Frequency Divider for older Oscilloscopes??
« Reply #52 on: July 19, 2021, 05:16:03 pm »
Quote
The Infiniim XUR series starts at 5GHz and goes to 110GHz albeit with only a 5bin ENOB. I can't afford one.

Opsss.. I must admit that I did not know him.
I am now in my 74's, I am retired, and I have not worked in any laboratory for more than 15 years.
I must admit that I have become somewhat out of date.
That's called "old age"....haha....
I guess that in 500 years the waves will be drawn in the air....  :-DD  :-DD
 

Online David Hess

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Re: Frequency Divider for older Oscilloscopes??
« Reply #53 on: July 19, 2021, 08:37:54 pm »
And yes, the sampling aperture does need to be <<1ns, but that is a very small part of the circuit: a pulse, a sampling diode, and a capacitor. High speed scopes typically have nothing else at the front end, and are rather fragile - just like spectrum analysers.

The sampler is a small part of the circuit but more than just a fast sample and hold because the gate time is much shorter than the settling time.  The schematic may show a switch followed by a capacitor but a lot more is going on and in practice the capacitance is actually a transmission line.

Modern high speed oscilloscopes are nothing like this and have a linear front end using exotic MMIC technology so closer to a traditional DSO except for the weird mixing and interleaving ones from LeCroy and Keysight.

Quote
Having said that, one of the few significant advances recently has been the stunning improvement in ADCs and DACs speed and resolution, thus making sampling bridge front ends less important than they were.

Modern ADCs are amazing.
 

Offline tggzzz

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Re: Frequency Divider for older Oscilloscopes??
« Reply #54 on: July 19, 2021, 08:55:30 pm »
Radio stops, by definition at 300GHz and IR begins.

Even at 60GHz a high gain ceramic antenna can be improved by adding a 1/4 wave anti reflection coating, just like an optical lens.
There are lies, damned lies, statistics - and ADC/DAC specs.
Glider pilot's aphorism: "there is no substitute for span". Retort: "There is a substitute: skill+imagination. But you can buy span".
Having fun doing more, with less
 

Offline Jorge Ginsberg

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Re: Frequency Divider for older Oscilloscopes??
« Reply #55 on: July 19, 2021, 10:24:06 pm »
Quote
"I want to observe a signal that is between 990MHz and 1000MHz. What is the minimum sampling frequency that I need to use?".

Those answering 2GS/s faced an uphill struggle...."

You can use any sampling frequency. What is of interest here is how fast the sample is taken, not how often that sample is repeated.
You can take samples at a rate of 1000 samples per second... 10,000 samples per second... etcetera. 
If a waveform is repetitive, you can take a sample every 1000 waves and still reconstitute the original waveform correctly.
Here the important thing is not the frequency but the duration of the pulse that takes the sample and being a frequency between 900 MHz and 1 GHz, whose period ranges from 1.11 ns to 1 ns, the duration of the sampling pulse should be of the order of 0.1 ns or less.
 

Offline tggzzz

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Re: Frequency Divider for older Oscilloscopes??
« Reply #56 on: July 19, 2021, 10:34:18 pm »
Quote
"I want to observe a signal that is between 990MHz and 1000MHz. What is the minimum sampling frequency that I need to use?".

Those answering 2GS/s faced an uphill struggle...."

You can use any sampling frequency. What is of interest here is how fast the sample is taken, not how often that sample is repeated.
You can take samples at a rate of 1000 samples per second... 10,000 samples per second... etcetera. 
If a waveform is repetitive, you can take a sample every 1000 waves and still reconstitute the original waveform correctly.
Here the important thing is not the frequency but the duration of the pulse that takes the sample and being a frequency between 900 MHz and 1 GHz, whose period ranges from 1.11 ns to 1 ns, the duration of the sampling pulse should be of the order of 0.1 ns or less.

The question did not specify that the waveform was repetitive, so that cannot be assumed.
There are lies, damned lies, statistics - and ADC/DAC specs.
Glider pilot's aphorism: "there is no substitute for span". Retort: "There is a substitute: skill+imagination. But you can buy span".
Having fun doing more, with less
 

Offline Jorge Ginsberg

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Re: Frequency Divider for older Oscilloscopes??
« Reply #57 on: July 20, 2021, 10:17:29 am »
Quote
"I want to observe a signal that is between 990MHz and 1000MHz. What is the minimum sampling frequency that I need to use?".

Those answering 2GS/s faced an uphill struggle...."

You can use any sampling frequency. What is of interest here is how fast the sample is taken, not how often that sample is repeated.
You can take samples at a rate of 1000 samples per second... 10,000 samples per second... etcetera. 
If a waveform is repetitive, you can take a sample every 1000 waves and still reconstitute the original waveform correctly.
Here the important thing is not the frequency but the duration of the pulse that takes the sample and being a frequency between 900 MHz and 1 GHz, whose period ranges from 1.11 ns to 1 ns, the duration of the sampling pulse should be of the order of 0.1 ns or less.

The question did not specify that the waveform was repetitive, so that cannot be assumed.

If you are talking about "frequency" and you mention "900 Mhz to 1000 Mhz" then you are talking about a repetitive signal.
And to capture a single pulse, which occurs only once and never repeats again I would never use a sampling scoloscope.  I would rather use an optical memory oscilloscope like the Tektronix 7000 series oscilloscopes had, capable of storing a pulse on the screen.
 

Offline tggzzz

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Re: Frequency Divider for older Oscilloscopes??
« Reply #58 on: July 20, 2021, 10:54:51 am »
Quote
"I want to observe a signal that is between 990MHz and 1000MHz. What is the minimum sampling frequency that I need to use?".

Those answering 2GS/s faced an uphill struggle...."

You can use any sampling frequency. What is of interest here is how fast the sample is taken, not how often that sample is repeated.
You can take samples at a rate of 1000 samples per second... 10,000 samples per second... etcetera. 
If a waveform is repetitive, you can take a sample every 1000 waves and still reconstitute the original waveform correctly.
Here the important thing is not the frequency but the duration of the pulse that takes the sample and being a frequency between 900 MHz and 1 GHz, whose period ranges from 1.11 ns to 1 ns, the duration of the sampling pulse should be of the order of 0.1 ns or less.

The question did not specify that the waveform was repetitive, so that cannot be assumed.

If you are talking about "frequency" and you mention "900 Mhz to 1000 Mhz" then you are talking about a repetitive signal.

No! Is an AM radio wave repetitive? Or FM etc?

Quote
And to capture a single pulse, which occurs only once and never repeats again I would never use a sampling scoloscope.  I would rather use an optical memory oscilloscope like the Tektronix 7000 series oscilloscopes had, capable of storing a pulse on the screen.

I have a dual beam Telequipment storage scope, for no good reason other than fun. Analogue storage scopes always were a pain, used when nothing else was available.

The early digitising scopes had severe limitations, but the current ones are remarkably good. While a good analogue scope is worth using, one-off events are the killer use case for digitising scopes.
« Last Edit: July 20, 2021, 10:58:13 am by tggzzz »
There are lies, damned lies, statistics - and ADC/DAC specs.
Glider pilot's aphorism: "there is no substitute for span". Retort: "There is a substitute: skill+imagination. But you can buy span".
Having fun doing more, with less
 

Offline Jorge Ginsberg

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Re: Frequency Divider for older Oscilloscopes??
« Reply #59 on: July 20, 2021, 11:22:04 am »
Quote
I have a dual beam Telequipment storage scope, for no good reason other than fun. Analogue storage scopes always were a pain, used when nothing else was available.

The early digitising scopes had severe limitations, but the current ones are remarkably good. While a good analogue scope is worth using, one-off events are the killer use case for digitising scopes.

More than 25 years ago, I used the Tektronix 7934 with analog storage and it was never a "pain"....
 

Offline tggzzz

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Re: Frequency Divider for older Oscilloscopes??
« Reply #60 on: July 20, 2021, 11:51:47 am »
Quote
I have a dual beam Telequipment storage scope, for no good reason other than fun. Analogue storage scopes always were a pain, used when nothing else was available.

The early digitising scopes had severe limitations, but the current ones are remarkably good. While a good analogue scope is worth using, one-off events are the killer use case for digitising scopes.

More than 25 years ago, I used the Tektronix 7934 with analog storage and it was never a "pain"....

I was using a 7k in the late 70s. Irritatingly unreliable, partly because of the plugin connectors.

I was using a 1GHz digitising scope in 1990, but the realtime sampling rate was much lower than 2GS/s :)
« Last Edit: July 20, 2021, 11:53:37 am by tggzzz »
There are lies, damned lies, statistics - and ADC/DAC specs.
Glider pilot's aphorism: "there is no substitute for span". Retort: "There is a substitute: skill+imagination. But you can buy span".
Having fun doing more, with less
 

Offline Jorge Ginsberg

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Re: Frequency Divider for older Oscilloscopes??
« Reply #61 on: July 20, 2021, 11:59:15 am »
Quote
I was using a 7k in the late 70s. Irritatingly unreliable, partly because of the plugin connectors.
may have been some equipment with problems.  In the communications lab where I worked we had two Tektronix oscilloscopes: a 7934 oscilloscope and a 7603 oscilloscope.  Both used plug in's and neither of them ever gave us any problems.  But I don't rule out that someone else might not have...

 


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