Frequency Divider for older Oscilloscopes?? - Page 1
Forum section: electronics / general

author: GlennSprigg
author_rank: Super Contributor
timestamp: April 02, 2020, 11:16:57 am
content: I can't find enough info about doing this. (Excuse my deteriorating mind!)Is there a 'relatively' simple way to create an external Frequency Divider, to say.. measure frequencies on an old 10-Mhz Analog Scope, such as a 'Divide-By-Ten' circuit to measure up to 100-Mhz?? I've seen some 'Counter' circuits that obviously would not retain anything of the original 'WaveForm', and at best could just count the Frequency, beit a simple SquareWave output. Maybe for the 'too-hard' basket?Yea, I know. I can hear people screaming... "Just buy a 100-Mhz Scope!" Sigh..

author: tggzzz
author_rank: Super Contributor
timestamp: April 02, 2020, 11:27:29 am
content: You need to define the input you want to observe. Consider especially the amplitude and range of frequencies of interest, e.g. 100MHz+-5MHz.If you are interested in seeing 0-100MHz on a 10MHz scope, forget it.If you are interested in 95-105MHz (i.e. 10MHz bandwidth) then you can use RF techniques to mix and downconvert the 100MHz signal to baseband.Another technique, which only works with repetitive signals, is to sub-sample the input. Many digitising scopes do that, but I suspect building an external sampler will be more than you wish to do.

author: David Hess
author_rank: Super Contributor
timestamp: April 02, 2020, 11:45:55 am
content: https://www.eevblog.com/forum/projects/diy-ghz-sampling-head-for-lt100mhz-scopes/

author: Ian.M
author_rank: Super Contributor
timestamp: April 02, 2020, 11:51:54 am
content: Errr.... *NO* a frequency divider circuit isn't worth doing - just get a 100MHz or better frequency counter. Its possible to home-brew a 100MHz frequency counter with a PIC18 (using its T0CKI Timer 0 clock input, which is good up to 50MHz if properly handled and can be backed by 24 bits of internal hardware counter - seeAN592for how to get the low byte out of the internal prescaler) + a fast D type flipflop to get it up to 100MHz, guarentee 50% duty cycle at T0CKI and also gate the input and allow AN592 prescaler access. If you need it to count slow or low level signals you'll need some sort of limiting preamp, and if you need to go above 100MHz, will need a prescaler. If you aren't already into PICsits better to buy a commercial instrument than to build!OTOH if you need to actually view fast repetitive signals, you could (in theory) build an analog sampling frontend. You'll need a very fast sample and hold, a fast trigger circuit, and an adjustable sampling clock gated by a monostable. Its also a bitch to build a properly compensated input attenuator and/or wide band preamp if you want a wide input range. Seehttps://en.wikipedia.org/wiki/Oscilloscope_types#Analog_sampling_oscilloscopefor a very brief intro + a few helpful links. However, unless you have most of the parts needed already gathering dust , lots of zero cost free time and nearly infinite patience with setbacks, you'd be better off buying a modern 100MHz or better DSO.Edit: David and Tggzzz are also suggesting analog sampling front ends.

author: 2N3055
author_rank: Super Contributor
timestamp: April 02, 2020, 12:08:41 pm
content: Quote from: GlennSprigg on April 02, 2020, 11:16:57 amBecause 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.

author: GlennSprigg
author_rank: Super Contributor
timestamp: April 02, 2020, 12:23:35 pm
content: To all, point taken and understood.

author: tggzzz
author_rank: Super Contributor
timestamp: April 02, 2020, 03:28:07 pm
content: Quote from: 2N3055 on April 02, 2020, 12:08:41 pmNot quite true. Back in the 70s I saw 10MHz waveforms captured and displayed on an XY pen chart recorderIf you have a sampling scope everything up to and including the sampler has to be full speed, but the rest can be as slow as is convenient.

author: Kleinstein
author_rank: Super Contributor
timestamp: April 02, 2020, 04:13:25 pm
content: Some older scopes used analog CCD like memories to first sample the signal relatively fast and than play it back at a reduced speed for the slower ADC. In principle this could be use, but those CCD memories, especially the faster ones are hard to get parts.

author: 2N3055
author_rank: Super Contributor
timestamp: April 02, 2020, 05:10:57 pm
content: Quote from: tggzzz on April 02, 2020, 03:28:07 pmThat was only display. You had 10MHz scope (sampler type) in front of it. I thought I explained what I meant. It was a 10 MHz sampling scope assembled from two devices, sampling head with S/H and pen chart recorder as display....

author: tggzzz
author_rank: Super Contributor
timestamp: April 02, 2020, 07:16:48 pm
content: Quote from: 2N3055 on April 02, 2020, 05:10:57 pmThe OP wants to see a 100MHz signal on his 10MHz scope. Thatispossible with a sampling front end.

author: 2N3055
author_rank: Super Contributor
timestamp: April 02, 2020, 07:31:16 pm
content: Quote from: tggzzz on April 02, 2020, 07:16:48 pmThat is what I'm saying too. And that comprises a sampling scope with required bandwidth.His original question whether he can down-convert the signal like it is done in direct heterodyne receiver, and look at it on 10MHz scope and preserve pulse shape of original signal. He can't.It wasn't discussion of how sampling scopes work.

author: tggzzz
author_rank: Super Contributor
timestamp: April 02, 2020, 08:35:45 pm
content: Quote from: 2N3055 on April 02, 2020, 07:31:16 pmIn the first post he is after frequency, not wave shape.In the second post I noted you can simply downconvert to below 10MHz.

author: 2N3055
author_rank: Super Contributor
timestamp: April 02, 2020, 08:46:34 pm
content: Quote from: tggzzz on April 02, 2020, 08:35:45 pmI went back an read it again. And now I must say you are 100 % correct about that. I was confused..Sorry about that and thank you for being patient with me and setting me straight..All the best,Sinisa

author: tggzzz
author_rank: Super Contributor
timestamp: April 02, 2020, 09:20:01 pm
content: Quote from: 2N3055 on April 02, 2020, 08:46:34 pmNo problem. We all make mistakes, but too few of us admit itBesides, some mistakes are more interesting than others

author: Jorge Ginsberg
author_rank: Contributor
timestamp: July 15, 2021, 10:42:01 am
content: Hello Mr. GlennSpriggI am new to this forum and just read your question.I am an Electronics Engineer but I am already retired. I live in Argentina and my English is very bad. I am writing to you with the help of "Google Translator".As your post is more than 1 year old, before answering I would like you to tell me if you have already solved your question so I don't write in vain. Best regards from Buenos Aires.(My sister lives in Australia, in Melbourne)

author: Ian.M
author_rank: Super Contributor
timestamp: July 15, 2021, 10:54:35 am
content: @Jorge,First, welcome to these forums.Quote from: GlennSprigg on April 02, 2020, 12:23:35 pmI would understand that as: Glenn accepts that his original question had no cost-effective practical solutions. However if you have built an analog sampling front end or other device to down-convert high frequency signals for display on a lower bandwitdh scope, we'd all be interested in seeing your project.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 15, 2021, 12:22:40 pm
content: Welcome Jorge,I don't mind seeing some of these more technical threads revived and am interested in hearing about what you have to offer.Some time ago I had downloaded the patents for LeCroy's Digital Bandwidth Interleaving and attempted to write a simulator to demonstrate how it works. Roger Delbue from LeCroy chimed in the comments and offered a few bread crumbs. The video starts out showing a home made Arb which can be used for this purpose. In the end of the video I show a down converter used to monitor the output of a simple oscillator I was playing with.At 12:40, I show another simple down converter using a DRO.

author: Jorge Ginsberg
author_rank: Contributor
timestamp: July 16, 2021, 12:42:30 pm
content: I am sorry to say but I too can only offer a few "crumbs"....Many ...MANY years ago (between 1980 and 1982), I built a prescaler that obtained an almost exact copy of an analog signal but with a frequency 100 or 1000 times lower. That mean that it was possible to observe a 100 Mhz signal as if it were a 100 Khz signal. It was entirely made with Shotky-TTL technology, something already obsolete or almost obsolete today.I can give the idea here but unfortunately I have sold and given away everything. Schematics included.It happens that I have been retired for 15 years now and as soon as I started to see this equipment coming from China, at such low costs, I realized that if I didn't sell my lab quickly I was going to be left with old or obsolete junk in my hands. Therefore, I hurried to sell everything. Now I just read about electronics. Nothing more than that.I regret not keeping the schematics. I was convinced that they were worthless obsolete things. I never imagined that someone would want to build an analog prescaler, being that nowadays you can get good sampling oscilloscopes for less than 400 dollars....If you still want to know how I did it and you want to develop it, just let me know and I will tell you -at least what I remember- how to do it.Greetings from Argentina

author: Jorge Ginsberg
author_rank: Contributor
timestamp: July 18, 2021, 09:10:05 am
content: Quote2N3055 : 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. And you can do it in analog form. No memory, no counter, no microprocessor. The only thing you could use is some high speed TTL chips and even not even that. And it's a relatively simple project, but very critical in terms of the semiconductors, capacitors and resistors you employ.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/Look also here:https://www.renhotecic.com/HANMAKET-DOS1102-110MHz-Digital-Oscilloscope-2channel-Oscillograph-1Gsa-s-7-Tft-LCD-Osciloscope-Kit-Better-Than-Ads1102cal-0004577But 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.

author: 2N3055
author_rank: Super Contributor
timestamp: July 18, 2021, 09:30:19 am
content: Quote from: Jorge Ginsberg on July 18, 2021, 09:10:05 amYou might knowwhat you're talking aboutbut youdidn't seem to understand what I didtalk 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,

author: Jorge Ginsberg
author_rank: Contributor
timestamp: July 18, 2021, 10:21:58 am
content: Quote from: 2N3055 on July 18, 2021, 09:30:19 amOK. 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

author: 2N3055
author_rank: Super Contributor
timestamp: July 18, 2021, 02:59:42 pm
content: Quote from: Jorge Ginsberg on July 18, 2021, 10:21:58 amYes, 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,

author: bdunham7
author_rank: Super Contributor
timestamp: July 18, 2021, 04:49:16 pm
content: Quote from: 2N3055 on July 18, 2021, 02:59:42 pmI 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.

author: Jorge Ginsberg
author_rank: Contributor
timestamp: July 18, 2021, 05:44:49 pm
content: 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.

author: Jorge Ginsberg
author_rank: Contributor
timestamp: July 18, 2021, 05:51:30 pm
content: 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.

author: tggzzz
author_rank: Super Contributor
timestamp: July 18, 2021, 06:11:23 pm
content: It strikes me that people in this conversation would benefit from thinking about how "Tayloe Mixers" work. Also see "Polyphase mixers" and "N-path filters".https://www.eevblog.com/forum/rf-microwave/polyphase-or-n-path-mixer/msg3381802/#msg3381802isn't a bad starting point, but there are probably better ones.

author: bdunham7
author_rank: Super Contributor
timestamp: July 18, 2021, 07:04:12 pm
content: Quote from: Jorge Ginsberg on July 18, 2021, 05:44:49 pmYou might want to draw a picture or something because something is missing here.If you take 10,000 samples at exactly the same rate as the input signal, which is what you seem to be implyiing, you'll have 10,000 of exactly the same sample--a flat line.Second, you are clearly not storing the samples anywhere, so how are you 'reconstituting the signal'? I believe the systems2N3055refer to require storing the samples.Third, are you implying that the fact that you take exactly 10,000 samples will result in an apparent frequency reduction of 10,000 times? I don't see how that would work and I don't see how your system could manage that in any case--it is too simple with just those components.The only way I can see something with that few components working is as some sort of mixer. You wouldn't have a schematic or anything by chance?

author: 2N3055
author_rank: Super Contributor
timestamp: July 18, 2021, 07:44:18 pm
content: Quote from: bdunham7 on July 18, 2021, 07:04:12 pmIt is called RIS (random interleaved sampling) and ETS (equivalent time sampling).You need to have a trigger circuit with very low jitter.You have a sample and hold circuit (S/H) that takes super short sample (let say samples single value for 100 psec) and keeps it for readout.So you trigger, and take a 100 psec sample. You then readout that value and read it with slow A/D converter. In meantime, millions of periods of signal passed by. But since signal is repetitive we don't care. After saving that first point, we rearm trigger, and wait for new one. When it fires, then magic hapens: we sample signal with a 100 psec delay from trigger. Sample and save that. Third time, we take sample at 200 psec delay. That way we reconstruct a waveform from many many different trigger events. Equivalent sampling rate would be 10 GS/sec.With RIS (random interleaved sampling) we also trigger, but it is upside down: we sample at random intervals, not sequentially from the trigger. But we do keep triggering, and measure time from trigger and sample so we know where to position the point in time domain. It is funny to look at how it assembles the waveform by plotting random dots left and right until it starts to resemble the waveform...That is how analog sampler scopes worked, with different details in implementation of S/H circuit, and actual timing and trigger circuits. Some samplers didn't even have real trigger circuit, but you had to provide trigger yourself, already conditioned...

author: bdunham7
author_rank: Super Contributor
timestamp: July 18, 2021, 08:28:34 pm
content: Quote from: 2N3055 on July 18, 2021, 07:44:18 pmI understand ETS and sampling scopes, I even have several still. I don't see how what Jorge is describing could possibly do any of those things.

author: Jorge Ginsberg
author_rank: Contributor
timestamp: July 18, 2021, 09:26:56 pm
content: A picture is worth a thousand words, the Chinese used to say.I would like to have a simple program with which I can draw sinewaves and other symbols to be able to explain in a single drawing what I find so difficult to explain with words...Does anyone know of a light program that would allow me to do that?

author: 2N3055
author_rank: Super Contributor
timestamp: July 18, 2021, 09:55:33 pm
content: Quote from: bdunham7 on July 18, 2021, 08:28:34 pmFunny thing is that sometimes non native English speakers understand better other non native English speakers because to us it is a logical process, not natural simple recognition. We go by logic of the said words and not by what it should be in good English. Trust me, he's is talking about sequential sampling principle (ETS style). And if you do 10000 points per second, you don't even need A/D and storage. You simply show it on slow CRT scope screen where phosphor persistence will act as a storage for some miliseconds, enough to build full screen.

author: Jorge Ginsberg
author_rank: Contributor
timestamp: July 18, 2021, 10:05:29 pm
content: I made this drawing using paint. It's not a good drawing, but just by looking at it you will understand exactly how I was able to get a 100 Mhz signal to transform into a 10 Khz signal. If the samples are thousands per cycle, the reconstituted waveform is a perfect copy of the sampled signal. See the attached png file.

author: bdunham7
author_rank: Super Contributor
timestamp: July 18, 2021, 10:52:04 pm
content: Quote from: 2N3055 on July 18, 2021, 09:55:33 pmSometimes by approaching things from different angles, two people can describe the same phenomenon in different ways. If you look at his picture and read my description, I think they match exactly. How would you describe that other than as an alias? It's only going to work if the sampling frequency is offset from the signal frequency slightly, and by a known amount if you want to have a predictable display.I'm not sure what you mean when you say that you can just put it on the screen at 10,000 samples per second. ETS also has a way of knowing the timing of each sample so that it knows where (horizontally) to display it. Can you show me an example where this would work otherwise? Without storing the samples, to put them up at the right position would require the sweep rate to be synced to the input frequency. Unless I'm missing something, which is always possible, I think the method described here is some sort of alias-based downmixing and can't work for arbitrary frequencies unless the sampling rate is somehow automatically tuned with a fixed offset.Now if the circuit is complex enough that it can trigger on the 100MHz signal and then produce a ramp to trigger the sample point at calibrated and increasing time offsets, then it might be able to accomplish the task without depending on any particular characteristic of the input other than repeatability. Then you'd have a phosphor-based storage sampling scope like you describe. I don't see that what he describes could accomplish all that--it would require a bit more complexity than he describes.

author: bdunham7
author_rank: Super Contributor
timestamp: July 18, 2021, 10:54:58 pm
content: Quote from: Jorge Ginsberg on July 18, 2021, 10:05:29 pmOK, but it seems clear that your sampling rate is just slightly slower than the input signal, not equal to it, right? How does the circuit determine and set the sampling rate?

author: Ian.M
author_rank: Super Contributor
timestamp: July 18, 2021, 11:05:43 pm
content: I agree with Bdunham. To down-convert a 100.000MHz signal to 10KHz, you need to sample at 99.990MHz, not at 100.000MHz. If you want to automate this so that the output frequency is always 1/10000 of the input frequency, at the very least you'll need a good VCO for the sampling clock that covers the input range you are interested in, and to PLL lock it to 9999/10000 of the input frequency (which is a whole other can of worms if the input is not a nice quasi-sinusoid).The requirements for the sample and hold are also rather stringent - it may well be easier to implement as a pair of carefully matched track and holds that alternate acquiring the signal, and a fast analog switch to select the one currently holding.

author: bdunham7
author_rank: Super Contributor
timestamp: July 18, 2021, 11:16:34 pm
content: Just to be clear, I'm not claiming Jorge is wrong or that what he says he made didn't exist, just that I don't understand how it would work very well given the description. I hope he is patient enough to continue the conversation and isn't put off by language barriers. He mentioned some TTL logic, so perhaps something like a 7474? which would imply some trigger logic. Making a workable trigger, ramp and sample/hold circuit that operates into the UHF region does not seem a trivial task.

author: Jorge Ginsberg
author_rank: Contributor
timestamp: July 18, 2021, 11:21:10 pm
content: QuoteNo...no...no... and NO.QuoteNo...no...no... and NO.What changes is not the frequency of sampling. What changes is the TIME at which the sampling occurs. In the first cycle, (for example) it occurs 1 picosecond after the wave starts (zero crossing from bottom to top). The second sample is taken 2 picoseconds after the zero crossing, from bottom to top.The third sample is taken 3 picoseconds after the zero crossing, from bottom to top.The fourth sample is taken 4 picoseconds after the zero crossing, from bottom to top.The fifth sample is taken 5 picoseconds after the zero crossing, from bottom to top.And so on until the cycle is complete.And if you use 10000 samples to reconstitute the original waveform, and you have taken only one sample for each cycle, then the reconstituted signal will have a frequency 10000 times lower and you will be able to observe it on a cheap oscilloscope.The sampled voltage is charged into a capacitor. And on that capacitor a perfect sine wave is obtained, and a faithful copy of the sampled signal.No A/D converters are needed. No need for counters. No need for memories. The method and the circuit are much simpler than you suppose. But you must use your wits to figure it out. That's the beauty of electronics design: the ingenuity you use to solve a complicated problem with a simple solution.The most remarkable thing about all this talk is thatGlennSprigg , the original author of the query, has not even shown up here......

author: bdunham7
author_rank: Super Contributor
timestamp: July 19, 2021, 01:29:10 am
content: Quote from: Jorge Ginsberg on July 18, 2021, 11:21:10 pmOK, let's reason through it so at least we agree on the steps needed. Then I'll think about how hard it would be to build.QuoteIn many things there are different ways of describing the same thing. Often two very descriptions will boil down to the same thing. In this case, at a given signal (say our 100MHz) sampling as you describe will result in a sampling frequency just under the signal frequency, just by a different method. In this case the method is important, but the result may be considered in different ways.QuoteOK, so to the meat of the problem. Someone correct me if I err. These are the issues, more or less in order. Assume a 100MHz input signal to be displayed at 10kHz.1. You need a way to trigger on the zero crossing (or anywhere, I suppose) of the input signal.2. You are sampling at 100MSa/s using an offset that cycles at 10kHz and has a range sufficient to cover one period.3. If you want to display this as single period 10kHz signal on a scope, the scope should have a sweep time of 100 microseconds.4. You need a method of offsetting samples of the input frequency from 0 to 10 nanoseconds, corresponding to one period.5. To display the samples on the scope, they have to be correlated so that their positions in real time on the scope are proportional to the sample offset time. So the +5nS sample must appear at the 50uS position.6. Since there is no storage, the samples have to occur in real time with the two values correlated. Thus you need a circuit that 'knows' where it is on the 100uS scale and offsets the sample by the corresponding amount.So you need a trigger that operates on the 100MHz input signal, a 10kHz ramp signal followed by an offset delay circuit that corresponds to the ramp and then operates the sample circuit. You can trigger the display scope on the 10kHz ramp or on the sampled output. Anything else?QuoteTime zones. We're all over the world and people pop in and out.

author: Jorge Ginsberg
author_rank: Contributor
timestamp: July 19, 2021, 02:55:15 am
content: QuoteThat's right.And any oscilloscope has a trigger circuit. There is no difficulty in that.QuoteI'm afraid I don't understand what you're sayingQuote.Once you have the reconstituted signal you send it to the oscilloscope of your choice. To the oscilloscope, that reconstituted signal is just like any other signal it receives. The oscilloscope is not obliged to know that you are feeding it a signal that was the product of another sampled signal... In fact, you are doing all this to be able to see VHF signals with your cheap oscilloscope...Quotefrom 0 to 10 ns... from 0 to 5 ns... from 0 to 30 ns... Whatever you need. This is varied with a potentiometer, preferably a 10 turns one.QuoteYou are not feeding any sampled signal to the oscilloscope. Your oscilloscope is receiving an already reconstituted signal and your oscilloscope doesn't care where that signal comes from nor does it care how it was created.QuoteNo correlation with anything is necessary. The circuit simply takes the samples one after the other, period after period, and a capacitor takes care of integrating everything and reconstituting the signal.What you must find out now is how to achieve that each sample is displaced with respect to the previous one and that this time is not modified, because if it is modified, the waveform will change and that is what we do not want to happen.QuoteNo. Nothing else.Put your ingenuity to work and see if you can figure out how to achieve all that in a simple way.Enjoy the challenge !

author: bdunham7
author_rank: Super Contributor
timestamp: July 19, 2021, 03:54:59 am
content: Quote from: Jorge Ginsberg on July 19, 2021, 02:55:15 amOK, I can see generally what is needed. Making a reliable trigger may not be an insurmountable challenge, but picosecond jitter.... I suppose it doesn't have to be that good to nominally work.Correlation will occur whether explicitly designed for or just an implicit result of things 'boiling down' to what they actually are. The oscilloscope timing just serves conceptually as a framework, I understand the circuit doesn't depend on it in any way.I'll letGlennSpriggpick this up if he is still interested.

author: tggzzz
author_rank: Super Contributor
timestamp: July 19, 2021, 08:02:15 am
content: Here's a simple question that I have asked interviewees in a job interview..."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.(And I'm not surprised that the OP hasn't had the courtesy to respond)

author: tggzzz
author_rank: Super Contributor
timestamp: July 19, 2021, 08:22:19 am
content: Quote from: bdunham7 on July 19, 2021, 03:54:59 amI have a 50 year old scope (battery powered, can be operated in driving rain and stored underwater). It displays signals up to 4GHz with, IIRC, 37kS/s. It contains transistors, 741s and a few SSI logic gates (dual JK flip flops and nand gates), but no memory or anything like that. Thefull service manualcontains schematics and circuit descriptions.Watching the display twinkle is hypnotic, but I can't capture the effect in a videoOr see the attachment for another example circuit, fromhttp://www.redrok.com/Circuits_1GHz-samplig-Oscilloscope-Front-End.pdf

author: Jorge Ginsberg
author_rank: Contributor
timestamp: July 19, 2021, 10:46:01 am
content: QuoteIf you use semiconductors for UHF, if you use very stable voltages, and if you use constant temperatures, the jitter and drifts are so low that you hardly notice it.

author: Jorge Ginsberg
author_rank: Contributor
timestamp: July 19, 2021, 11:18:06 am
content: Quote from: tggzzz on July 19, 2021, 08:02:15 amDear TGGZZZ... what kind of waves do you expect to find between 900 Mhz and 1000 Mhz? do you expect to find square waves? do you expect to find saw teeth?When you work in the high UHF zone and enter the microwave zone, ALL waves are already sine waves.An oscilloscope is useless at those frequencies.At very high frequencies, a resistor can behave like a coil and a capacitor can behave like a delay line. Transistors already behave differently. The "h" parameters are no longer used in the design, but the "s" parameters are used.At very high frequencies all the electronics change.Intel uses UHF and microwave engineers for the development of its chips. Imagine a microprocessor running at 3.6 Ghz.....A good technician or engineer in audio or industrial electronics becomes a perfect ignoramus when working above 1 Ghz.It is true that to observe correctly a 100 Mhz square wave you would need a 1000 Mhz oscilloscope, otherwise the square wave would be very distorted in its rising and falling edges; but it is never necessary to "look" at 1000 Mhz waves. In the vast majority of cases it is enough to know if that wave exists and what is his amplitude. For example, people who buy the Tektronix MDO3000 oscilloscope, whose bandwidth is 1Ghz, do not do it to see 1 Ghz waves but to be able to see correctly the 100 Mhz waves, because when you look at a 1 Ghz wave, the only thing you see is a sinewave...Those of us who work on UHF or microwave radio links only use spectrum analyzers. By looking at the spectrum you know if you have just a sine wave or if you have a more complex wave. In that frequency range it doesn't matter the shape of the waves, the only thing that matters is their harmonic content.

author: Jorge Ginsberg
author_rank: Contributor
timestamp: July 19, 2021, 11:34:39 am
content: The good thing about all this talk is that it doesn't end in a production.I say again what I said before: nowadays none of this is worth it. You can buy a good 100 Mhz oscilloscope for 400 dollars or even less.The appeal of all this talk is that we exercise our minds and find out how this device can be created analog, cheap and simple.Think of the human ingenuity displayed throughout history.In 1879, Albert A. Michelson measured the speed of light. At that time, laser beams did not exist. There were no atomic clocks.Michelson measured the speed of light using only mirrors and a rotating disk. And he determined the speed of light with an error of only 200 miles/hour !! AWESOME ...In 1653 the astronomer Christiaan Huygens determined the distance between the earth and the sun. What technology existed at that time to achieve such a feat?And more than 2500 years ago, the Babylonians already knew that the Earth was round and even calculated its diameter.And all this was achieved thanks to human ingenuity.That is why I wanted to tell you here that more than 30 years ago I built a device that allowed me to see UHF signals on a modest oscilloscope with a bandwidth of only 10 MHz. And I will give you hints about how I did it because the truly beautiful thing about electronics is the way it sharpens our ingenuity.If GlennSprigg was expecting to receive a ready-made design and simply copy it... I'm sorry to disappoint him.

author: bdunham7
author_rank: Super Contributor
timestamp: July 19, 2021, 01:55:55 pm
content: Quote from: tggzzz on July 19, 2021, 08:02:15 amSo I might respond by asking you to define the term "observe" and also ask whether "between 990 and 1000MHz" means the entire spectrum of the signal falls between those bounds. Would you respond or send me packing?Obviously sampling scopes can display anything that they can get a stable trigger on with an arbitrarily low sample rate if you are patient, but that doesn't mean they are cheap or easy to build.Quote from: Jorge Ginsberg on July 19, 2021, 11:18:06 amA lot can happen in a nanosecond these days....

author: Jorge Ginsberg
author_rank: Contributor
timestamp: July 19, 2021, 02:48:49 pm
content: QuoteYes... but are you sure that what you are seeing is exactly what is happening?When you measure signals in the microwave region you can never believe the waveform you are seeing.Cables... connectors... even reflections of possible waves in the cabinet or shields ... all can alter the signal you are looking at.When you open up a UHF circuit that is tucked inside a shield and try to observe some waveform, you are altering everything.believe me... above 500 or 1 Ghz you work with spectrum analyzers, not oscilloscopes.In the most extreme case, it might be necessary to observe some trigger pulse that lasts several nanoseconds... but there you are not talking about frequency but time. That trigger pulse could be repeated at the rate of one pulse every millisecond. And someone could say "the frequency of the pulse is 1 kHz". Nothing more wrong. NEVER confuse times with frequencies when it comes to laboratory measurements.

author: tggzzz
author_rank: Super Contributor
timestamp: July 19, 2021, 03:03:00 pm
content: Quote from: Jorge Ginsberg on July 19, 2021, 11:18:06 amIt is irrelevant, but you can consider a modulated signal.QuoteEr, that's true in any frequency band.If you don't like 900/1000MHz, divide it by 1000 or 1000000 and the question is equally valid.QuoteThere are 110GHz real time scopes commercially available. The Infiniim XUR series starts at 5GHz and goes to 110GHz albeit with only a 5bin ENOB. I can't afford one.Now, how do you think Keysight implements it? With a >220GS/s 5 bit ADC? I doubt it (but haven't bothered to research the implementation), and I suspect the reason is a direct consequence of correctly answering my question.Whether a scope is the right tool is a separate issue; frequently it isn't.QuoteTrue but irrelevant to the point.QuoteMy question is important for far more than scopes.

author: tggzzz
author_rank: Super Contributor
timestamp: July 19, 2021, 03:08:13 pm
content: Quote from: bdunham7 on July 19, 2021, 01:55:55 pmNo, 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 pointQuoteTrue if the signal is repetitive, but for a non-repetitive signal you have to capture it all on the fly (i.e. realtime).

author: tggzzz
author_rank: Super Contributor
timestamp: July 19, 2021, 03:11:08 pm
content: Quote from: joeqsmith on July 19, 2021, 02:07:00 pmNon-repetitive. You need to capture it alll as it occurs.

author: bdunham7
author_rank: Super Contributor
timestamp: July 19, 2021, 03:26:43 pm
content: Quote from: tggzzz on July 19, 2021, 03:08:13 pmI'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 needat least20MSa/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.

author: tggzzz
author_rank: Super Contributor
timestamp: July 19, 2021, 03:49:04 pm
content: Quote from: bdunham7 on July 19, 2021, 03:26:43 pmYou'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 thestunningimprovement in ADCs and DACs speed and resolution, thus making sampling bridge front ends less important than they were.

author: Jorge Ginsberg
author_rank: Contributor
timestamp: July 19, 2021, 05:16:03 pm
content: QuoteOpsss.. 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....

author: David Hess
author_rank: Super Contributor
timestamp: July 19, 2021, 08:37:54 pm
content: Quote from: tggzzz on July 19, 2021, 03:49:04 pmThe 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.QuoteModern ADCs are amazing.

author: tggzzz
author_rank: Super Contributor
timestamp: July 19, 2021, 08:55:30 pm
content: 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.

author: Jorge Ginsberg
author_rank: Contributor
timestamp: July 19, 2021, 10:24:06 pm
content: QuoteYou 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.

author: tggzzz
author_rank: Super Contributor
timestamp: July 19, 2021, 10:34:18 pm
content: Quote from: Jorge Ginsberg on July 19, 2021, 10:24:06 pmThe question did not specify that the waveform was repetitive, so that cannot be assumed.

author: Jorge Ginsberg
author_rank: Contributor
timestamp: July 20, 2021, 10:17:29 am
content: Quote from: tggzzz on July 19, 2021, 10:34:18 pmIf 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.

author: tggzzz
author_rank: Super Contributor
timestamp: July 20, 2021, 10:54:51 am
content: Quote from: Jorge Ginsberg on July 20, 2021, 10:17:29 amNo! Is an AM radio wave repetitive? Or FM etc?QuoteI have a dualbeamTelequipment 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.

author: Jorge Ginsberg
author_rank: Contributor
timestamp: July 20, 2021, 11:22:04 am
content: QuoteMore than 25 years ago, I used the Tektronix 7934 with analog storage and it was never a "pain"....

author: tggzzz
author_rank: Super Contributor
timestamp: July 20, 2021, 11:51:47 am
content: Quote from: Jorge Ginsberg on July 20, 2021, 11:22:04 amI was using a 7k in the late 70s. Irritatingly unreliable,partlybecause of the plugin connectors.I was using a 1GHz digitising scope in 1990, but the realtime sampling rate was much lower than 2GS/s

author: Jorge Ginsberg
author_rank: Contributor
timestamp: July 20, 2021, 11:59:15 am
content: Quotemay 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...