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Cheap PC Oscilloscopes - Any Recommendations?
Missionary Man asks: "I'm an electronics teacher looking for a good (but reasonably cheap) PC based oscilloscope for classroom demonstration purposes. I've done a reasonable amount of research and come up with a few contenders. Ideally I'd like something with a bandwidth of up to 40MHz and 2 channels. Does anyone have any tales to tell regarding the use of any of these scopes (or any others I haven't found or mentioned) and can recommend a suitable device?"
"Here's the list of my findings so far:
- The DS2200C from USB Instruments will do 2 channels at 12 bit resolution, but only to 200KHz.
- The PCS100 from Velleman at QKits runs to 12MHz, but only 1 channel. It has a bigger brother, the PCS500, that has 2 channels and 50MHz bandwidth, but is a lot more expensive.
- Picotech do cheaper ones, like the ADC-40/42, but these only operate in the KHz ranges.
- Link Instruments sell the DSO-2102S that runs to 60MHz with 2 channels, but it's a bit out of my price range.
- Finally, I found the bitscope which seems to be just what I'm looking for, combining a 2 channel scope and an 8 channel logic analyzer for a reasonable price.
I see them on case modding sites occasionally. As far as your use, I'm not sure how they would measure up. Knowing the thriftiness of many modders, you may be able to find a decent recommendation there.
Check this one out. . . I don't know the price because their price page is broken. . . It looks like everything you need in a PC Oscillioscope.
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Another lame blog
This is a little bit OT, but you can write off any purchases required for work, this includes education. Perhaps writing off that expensive oscilloscope would be equivalent to not writing off a less featured model.
Price page is here but it looks like it's around $900.
Err... I came up with a 5-figure, used, standalone HP.
Was that supposed to be funny?
Ce n'est pas un vrai mouvement de robot!
For cheap demo purposes, consider using the analog sound ports (line-in). I have had good success doing that for lower speed (44.1K).
I was looking for a PC based scope but couldn't find quite what I wanted.. I recently bought a used Tektronix 2215 for $50.
Some more info:s ds_more infos.htm
r oup/tan dm/news/31646
http://www.redacom.ch/messtechnik/softdsp/
This site lists the price as US $930.
http://www.techonline.com/community/tech_g
People that believe in their opinions don't post AC.
Remember that the oscilloscope bandwidth close to the frequency of the waveform being measured distorts that waveform. (In phase if the frequency being measured is a sine wave.) You need an oscilloscope bandwidth maybe 3 times the highest frequency being measured.
ICs often have very high potential bandwidths, and, when something goes wrong, even an audio IC can have sometimes have parasitic oscillations at extremely high frequencies. If you are working on a circuit, you need to be able to see those parasitic signals.
I don't like this fact, because it is expensive, but 100 MHz seems to be a good oscilloscope bandwidth. I bought a very old Tektronix scope to get the needed bandwidth at a reasonable price.
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OK, I know you asked about PC based scopes but if a plain old scope will do the job consider used.
A friend of mine bought a couple at a ham radio swap meet from a guy who buys surplus lots. IIRC they were dual-trace and something like 20MHz (he ended up getting one for me and for several other interested friends).
They were selling for ~$20 which means you could have a scope for every student in a class of 20 and still stay in your budget.
~~~~~~~
"You are not remembered for doing what is expected of you." - Atul Chitnis
I also have an Ozi-Fox handheld that has a PC and/or palm-based interface. It only does 20mhz and is single trace, but they are fairly inexpensive (< $90.00 USD) -- you could buy multiple units for classroom use. The display on the unit itself is not great, but works well for quick-and-dirty work.
Good luck -- m
Roving Web-Teleoperated Robot
It seems people on slashdot are a bit overeager to buy PC based devices that can't be used as a standalone device. So far that I've seen, the benefits are mostly just cost, at the expense of portability, usability and quality.
I'd just find a real scope on surplus somewhere.
I just have a 'scope on "loan" from a local EE guy. Just an analog one. Effectively it is mostly a gift, but there are times he wants an analog scope so he wanted the understanding that he can get it back on occasion. For most uses, a digital one does fine.
It is not difficult to find a veritable mount of cheap oscilloscopes on eBay. You say you only need it for demonstration purposes, so why do you need something shiny and new? It can even be argued that the older analog oscilloscopes are better than newer digital ones. As always, resort to eBay if you need something not so good, and fairly cheap. Chances are you can find it there.
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I found their price list page through the google cache...seems like their stuff is out of his price range, but here's the link anyhow:
SoftDSP Price List
If a 2 channel audio frequency scope is all you need, then Oscilloscope 2.5 for Windows might do the trick. It uses the inputs on a standard sound card to grab 2 channels at up to 20 kHz. Disclaimer: I've not used it and a bit of Googling may find better alternatives.
Its slow, but is free (assuming you have the sound card).
Two wrongs don't make a right, but three lefts do.
... can download free/open-source plotter emulation software at http://www.qsl.net/ke5fx/misc/7470.zip. This may be helpful to you if you buy an older scope from eBay. It will let you grab screenshots, overlay them, print them, and save them in several formats including their original HP/GL-2 plotter language. You can see some typical screen captures at http://www.qsl.net/ke5fx/synth.html.
I use a Tek 2430A on my own bench. These are great scopes -- you can get 150 MHz bandwidth for about $400-$600. A National Instruments GPIB adapter to interface it to the PC will set you back another $100.
I'm trying to add support for as many instruments as I can to this package. Any interested parties should feel free to email me...
Dahlmann tightly grips the knife, which he may have no idea how to use, and steps out into the plain.
If my understand is correct, some of the guys from the GNU Radio Project have developed a USB based software radio device that works with in linux. It is called the Universal Software Radio Peripheral. I think the first prototypes have shipped. The cost is pretty close to your price range. You can see it in action running an oscope program here. And of course it can be extended to do many more exciting things.
106dB isn't a sample rate, that's gain...
I think the real issue with using a soundcard *is* the sampling frequency (44kHz? 96kHz maybe?) and you'll probably let out the magic smoke if you plug more than a few volts into it so you need some sort of voltage divider there for many signals. Plus I don't know how much filtering is done on the line-in side.
That said I'd say it may be more cost effective to get some used stuff. I spent about $100 on ebay for an old Tek 465. 100MHz, good condition. And I can jam the probes into a wall socket with no worries. Good enough for most of my purposes. In college we had nice digital storage scopes (and at work we've got the fancy color ones) so now I've been spoiled. But I think if you're gonna teach kids how to use a scope it's best to use the real thing. I like the nice clicky knobs on the old Teks.
Since no one who's replied has answered your question, instead choosing to talk about unrelated things, I have to say that I'd go with the Bitscope.
Visit #electronics (our electronics+open source channel) on irc.freenode.net if you want to discuss.
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My understanding is that sound card inputs are AC coupled, so you won't be able to see anything much slower than about 20 Hz. That might be OK, but it's not quite an oscilloscope.
The bitscope only has a 40MS/s data aquisition rate. Assuming that that's for both channels - 20MS/s each, then your left with a nyquist of 10Mhz. And you really need to oversample a waveform a lot more than x2 to see what it looks like. The analog bandwidth of the bitscope is high, but the A/D conversion will result in a lot of aliasing. That said. Its a really impressive unit for $400.00. I didn't think you could find something nearly that fast for under $700. Not exactly what you're looking for.
The software for a scope is pretty important - but without the raw A/D speed and resolution you won't get very far.
Yes, that was supposed to be a joke. That is probably one of the highest-end oscilloscope anywhere in the world.
It's funny. Laugh.
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You don't need 10x samples for most things. You need around 5x to catch most transient events. You only need 2x to make a waveform per Nyquist.
Most digital scopes do a sort of interpolation when the frequency is above Nyquist, they will sample the signal for several periods and reconstruct what the waveform looks like, this works with any repeating signal, but when you use this you can't catch transient events, for that you do need a sampling rate several times the base frequency.
I've had enough abrasive sigs. Kittens are cute and fuzzy.
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DRMO = Defense Reutilization Marketing Office
This is the military agency that sells surplus equipment to the public. They usually have stuff like what you need.
If you can find something that has a HPIB/GPIB bus connector (IEEE-488) then you can connect it to a PC and use program your own interface (the libraries are very simple and very well documented). We did this both in the Army and also at a commercial satellite communications company (ours was to interface with HP spectrum analyzers thru IEEE-488).
Pedro
----
The Insomniac Coder
The other thing that should be mentioned is the fact that the line input doesn't exactly qualify as calibrated. Whilst this doesn't always matter too much, it is still a limitation. You'd need a good known signal level (AC signal, obviously) to provide any form of (non-NIST-traceable) calibration.
Also, don't forget that the input range is very limited. In order to provide a useful voltage range you'd need to build an instrumentation amplifier. This entails time, money and effort. By the time you've added a couple of useable probes, you've spent over $100 for a 2 channel 22KHz bandwidth non-calibrated AC-coupled only scope.And we haven't even discussed software :o
Personally, I think that trawling ebay is a much better proposition. I know from experience, having built a soundcard scope previously. After a few months trawling ebay I hit the jackpot and won a poorly described auction resulting in a Tek TDS360 for about $150. It also came with a Tek PS280 power supply and a BK Precision 4040A. Yep, about $3200 from reputable dealers...
Granted, that was a case of extreme luck, but if you're patient and you brush up on your ebay searchfu you should still do way better than a soundcard scope.
There are some reasonable PC-based scopes, (eg the Bitscope mentioned in the submitted article), but second hand Tektronix scopes from ebay are still better value IMO.
Beat it against a local oscillator set to a frequency such that the difference of the two lands between zero and 20 thousand cycles per second (Hz). It's called heterodyning and has been used to shift frequencies since the early days of radio if not before.
I see even classic Slashdot is now pretty much unusable on dial up anymore.
Happy memories of my 2340A, but I dunno if I ... they ran so hot, and their
would recommend spending cash to buy one on
the used market
mean-time-to-failure reflected it. We had a few
dozen under our control (research lab + class lab),
and there would always be a few with little yellow
Post-Its on them waiting to be sent out for repair.
softdsp.com
I bought one two years ago (around 800$ canadian)
it's pretty good, does 200 MHz / (5 GigaSamplesPerSecond equiv., whatever that means), two channel, USB.
The software isn't great. I don't think there is a linux port... I'm lazy, haven't checked recently.
The actual device is really sweet. If I haven't blown it up in two years, it is pretty solid! (I'm a chemist, and I do things like attach 400V power supplies to it randomly, I'll feel bad if it dies. Or me.)
Good luck!
If you really want to give your students a head start, I'd suggest finding any cheap scope with a GPIB interface and get an educational copy of the LabView software
http://www.ni.com/academic/edu_dsct.htm
(you should double check that the educational version actually supports GPIB because I don't recall if it does).
There's a hell of a lot of corporations out there that use LabView for all their test equipment, so there's a good chance your students will run into it when they get jobs.
Many people make them, and they are real oscopes on
a PCI card... but the ones I have used were GaGe...
http://www.gage-applied.com/
Should not be too pricey, and I think they have
educational discounts. They are the best option
I have seen to get a real oscope in a computer, and
the sampling rate and digitization will beat a sound card hands down.
Personally you have to be careful about many of the "PC" based scopes that are out there. They usually suffer from bad analog bandwidth and short memory depth. Also you have to pay particular attention to many of the voltage/impendance limits of "PC" scopes.
Personally taking a trip down to your local electronics swap meet is not a bad idea if you have one nearby. Hear in SiValley there are a few around on the weekends where you get some older Tek/HP *cough* Agilent scopes for pennies on the dollar. Sometimes they need some work but most people are honest about it.
-Ho
The other thing to consider is the input amplifier bandwidth (this applies both to analog and digital scopes). This is also known as slew rate. It describes how fast the input amp can follow a signal change. Imagine an ideal square wave with zero rise time. It has infinite bandwidth. What does this mean? If the signal has a faster riset time than your input amp, your edges will be smoothed out. If I look at the output of a 40 MHz TTL oscillator (which outputs a squarewave) with my 60 MHz scope, I see what is almost a sinewave. "60 MHz scope" means the scope can display a 60 MHz sinewave. The sinewave is the waveform with the slowest slew rate. All other 60 MHz waveforms will also look like a sinewave on this scope. If you want to analyze square waves, your scope will only show a halfway accurate depiction of the signal if it has upwards of ten times the bandwidth of the signal.
There are also problems when measuring high bandwidth signals. Above about 80 MHz, you need to use BNC jacks on both sides, properly terminated with 50 Ohms, or the stuff you see on your scope screen will have very little to do with the actual signal. Not many outputs can drive 50 Ohms. You need to build special prototypes of your stuff that are intended for scope measurements. You can't just take a scope to your CPU or stuff like that.
If I had to make a recommendation, get a 60-100 MHz analog scope in good condition. Tek 465 is a good model.
If you want to look at digital stuff, get a logic analyzer. There are some interesting DIY projects on the web.
For higher frequency or RF stuff, a spectrum analyser can't be beat. But good ones cost more than a luxury car. If you're really serious, there are DIY projects on the net for that, too.
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Nyquist is about waveforms. If you don't understand the relation between waveforms and frequencies, then you and I are just going to have to drop this conversation right now.
You need 2x samples to capture a waveform. Mathematically. However, we are in the real world, and 5x is considered generally adequate. Truthfully, most engineers won't let a 40MHz scope anywhere near a 40MHz signal; equipment doesn't tend to perform optimally at its edges.
As to why buy a digiscope for repeating signals: data capture is nice. Especially when you can capture raw sample values and spit them into MATLAB to do some serious data analysis. Also, there's the fact that you can't buy new analog scopes anymore. Finally: most DSOs will also function as a spectrum analyzer. Which is great on your repeating signals.
Could a circuit be devised that would take an external frequency outside of hearing range, and enable it to be fed into the audio input of a soundcard, so a media player's oscilloscope would work?
A sample-hold should do it. Run the sample-hold at the same frequency that you are running the sound card sampling. Essentially you fold the higher frequencies into the sound cards range and since you are doing an ocilloscope you use software to offset each cycle of sampling and build up your picture of a cycle over several cycles. By the time you had that all figured out you'd be better off with the scope card and software. Especially since the sound card won't do DC-30Hz. Interesting idea though.
90% of the wealth is in 2% of the pockets. Bummer to be in the majority.
I don't know if you are considering used or not, but if you are...
l
SurplusShed is a site where I've bought optics from time to time, but they carry some electronics also.
To quote the website:
http://www.surplusshed.com/pages/item/r1456.htm
This is a powerful 100 Mhz oscilloscope with 5 channels and 12 traces. It has a four way trigger off either channels 1, 2, 3, or ALT. Trigger lock for stable automatic triggering for complex signals such as video waveforms. Can display several Lissajous patterns at the same time. 5 mV to 5 V per division (1 mV with magnifier) and 2% accuracy. Sweep speeds are 20 ns to 500 ms. This is the scope that is being used in production, testing, R&D, and home shops because of its versatility and portability. Tested and in good working condition. Complete manual copy included. Only have a few."
Oops, forgot to grab the price, but it is around US $225
Anti-gravity? That was *my* little secret! But I never patented it! Boy, was *that* dumb!
That's what a hacker do - take some existing tech and use it in new ways. If you can live within the frequency range of sound (up to 96khz, for most cards) a sound card is an excellent tool for signal analysis. Plus: there's already many tools and libraries out there for audio manipulation - Heck! you could probably even write the software for you needs in Python!
I bought a DSO-2100 from Link Instruments and have been very pleased with it. Probably one of the best investments I've ever made.
I have an Optascope 81M USB scope from
http://www.optascope.com
I recommend it highly. Nice software and really works well for me. Also only $189.00!
Specs are:
1 Ms/S Maximum Sample Rate (500Ks/s 2 channels)
200 KHz Bandwidth
20Vpp Max Input for CH1 & CH2
8 Bit Vertical Resolution
2 Channel
External Trigger Source
Trigger on Rising or Falling Edge at Any Voltage
Variable Trigger Voltage on DSO channels
10%, 50% and 90% Horizontal Trigger Position
Auto or Normal trigger modes
USB interface
This was covered a few years ago; no surprise that most people forgot. The answers are mostly the same; still a good read though: http://ask.slashdot.org/article.pl?sid=01/12/07/19 1220&mode=thread
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Trogdor the Burninator!
You can get a new Tektronix 1002 (two channels, 60 MHz) scope for $995 without any educational discount. If I were in the market for a scope, I'd try to find one of those used. They're small, reliable, and inexpensive for their abilities. $400 is a probably low, but I wouldn't be too surprised to find one for $600. To me, learning to use the controls on a standard scope is worth quite a bit. (An extra $200? You be the judge.)
Good point. I know my last client was a wireless equipment manufacturer and when they went from 900MHz for 802.11 to 2.4 Ghz for 802.11b their old equipment was worthless because it mostly topped out at 1GHz. The old equipment was sold off to employees but they probably would have been just as happy to give it to an educational institution if they had been asked.
There are 4 boxes to use in the defense of liberty: soap, ballot, jury, ammo. Use in that order. Starting now.
For used scopes:http://sphere.bc.ca/test/
While you are at it, grab some slide rules and Nixie tubes.
"As God is my witness, I thought turkeys could fly." A. Carlson
There are a quite a few used Tektronix 465 scopes going for about $200. Check newsgroups, eBay and go to some Hamfests.
Wansu, th' chinese sailor
The most common source for these type of PC-card "instruments" is National Instruments.
If you are teaching about electronics, you would be better off buying a used Tek 475 (or similar) analog scope, you can get a very good one for $300-400. They can learn about the actual circutry, timing, measurement error, etc. without
getting heavily into sampling theory and digitial
signal processing.
If you want the students to learn "the new way" of
electronic instruments, check with National Instruments about used/traded in cards, and software; they may have an educational discount.
There are also some "poor man's" type of scopes made of surplus parts, old TV's, etc.. that you can find in the back pages of Nuts& volts magazine; I don't recommend these if you want the students to learn what they will use in the future, in real-world engineering applications.
Finally, there are mixed-mode instruments that are analog with analog storage, analog with digital storage, analog with digital readouts added, various standard instruments with serial or GPIB interfaces, and s/w from the mfr or 3d party for
control and analysis.
See if you can find on some engineer's shelf a catalog/book from Tek or HP, say, from the 1980s
or 90's, this is about the vintage that will work and be in your price range.
Calculate 10 samples per Hz of the signal that you're sampling
Why? Remember Nyquist theorem? Yes, you can't get perfectly square filters, but a 10x oversampling is a big overkill.
Check out the PCI/PXI/AT/USB/PCMCIA-5102 from National Instruments. I think they're about $1200 or so and 20 MHz 2-channel 8-bit, a little more than you wanted to pay but it's good stuff.
Modern circuits are not so well controlled as someone might guess. To have 20 kHz output with little phase distortion, it is necessary to pass more than 200 kHz.
But that's not the issue. ICs allow the design of circuits with bandwidths that are literally physically impossible with discrete components. The fundamental bandwidth limitations of the transistors used in the IC may be 200 MHz or more, or even 1.5 gigahertz. Any small problem can cause a circuit to oscillate at 50 MHz, even if the IC is supposedly limited to far less than this.
All you need for oscillation is gain and some positive feedback. In the real world, circuits try all possible combinations almost instantaneously, and begin oscillating for reasons the designer never foresaw. For example, maybe there is capacitive coupling through the IC packaging, and the output circuit alone is oscillating.
This is only a slight exaggeration: There are 4 steps toward making a new electronic device: 1) Build the circuit. 2) Supply power for the first time. 3) Apply an oscilloscope probe and begin discovering all the reasons the circuit is oscillating when it shouldn't. 4) Then discover all the other reasons the circuit isn't working correctly, if any.
I was never a person who thought that killing people and destroying their property was a good way to resolve social problems, but at one time it was my job to repair the automatic flight control systems of fighter-interceptors in the U.S. Air Force's Air Defense Command.
These aircraft required 250 hours of maintenance per hour of flight. (Aircraft meant to be sold to other nations, also, required 15 hours of maintenance per hour of flight. I've followed the development of weapons systems ever since, and my opinion of what is actually delivered is that it is often fraud, or close to fraud. United States taxpayers: Your assigned duty is to find the money to pay, and to avoid thinking.)
Anyhow, during training flights it was required to pull several g's. Sometimes at high accelerations the electronics would go completely crazy, and all inertial reference would be lost. The only fix for this at the time was to land, regain stability, and take off again. The aircraft that had this problem were therefore not much use for any situation actually requiring defense. Worse, the problem seemed to have nothing to do with any particular aircraft, but seemed random.
One day while trying to make a faulty system work on my bench test mockup, I discovered the reason. Some of the amplifiers that controlled the gyros had high frequency parasitic oscillations at perhaps 100 times the normal frequency of operation. You couldn't see the oscillations with normal equipment because the frequency was too high. I had borrowed an oscilloscope from some co-workers who worked on faster electronics.
The design of the amplifiers was acceptable, but many of the amplifiers had bad solder joints. Those with bad solder joints would oscillate; oscillating amplifiers would amplify at the required low frequency, but had a much smaller dynamic range than amplifiers that were not oscillating. (Yes, that bad solder joints could cause this doesn't make much logical sense, but most parasitic oscillations don't make much logical sense.)
The amplifiers had other defects that caused them to have a high failure rate. Every time an amplifier was pulled from an aircraft for a conventional repair, an amplifier was drawn from stock and put in the waiting aircraft so that the aircraft would be immediately operational. That was the reason the instability problems kept moving from aircraft to aircraft.
I drew a circuit diagram of my test setup, wrote an article about the problem, had a photographer take photos of the test setup, took screen photos of the parasitic oscillations, and sent everything to those who review such things. This had several effects. Someone at Air Defense Command headquarters wrote a letter praising my work. When everyone was reviewed for p
So modulate in hardware and demod to baseband in software.
With a simple analog multipler (for example, the Analog Devices AD834) and e.g. a 5 KHz oscillator, you can AM a band-limited (say, DC-500 Hz) signal, put it in your sound card, then do the demod in software (another multiplication will work).
This will cost you, in total, about $5 (you can get free samples of the AD834 and you'll need some resistors, some caps, a couple op-amps, and some wire) and will give you DC-500Hz through your modulator or 20Hz-24KHz without it. Not too shabby, especially compared with $500.
By the way, if you're going to spend $500ish anyway, why not pick up a Tektronix 2445 or 2465 on EBay? The 2465 has 350MHz bandwidth and is, IMHO, one of the nicest all-around scopes out there.
A 465 is good, but a 465B is better. The Tek 465 is about 30 years old now, and the 465B is only 20 years old. I was able to pick up a nice 465B with all manuals and accessories on eBay for $100 recently.
If the poster really wants a digital oscilloscope, head on over to fpga4fun.com. There's some neat little FPGA projects, based on a little FPGA board the guy designed and is now selling for $50. One of the applications is a digital sampling oscilloscope; it actually looks pretty neat. With the FPGA board and ADC board, it's pretty cheap too.
...
You might want to check out the boards put out by Interface, a Japanese company. Specifically, their PAZ-3161 board supports up to 40 MHz sampling rate (one channel; 20 MHz if you sample both channels). Not only does this company make excellent boards (my lab has several), they provide both Windows and Linux drivers for the boards.
I've done some preliminary work on writing signal-analyzer software for their PCI-3525 board, which I would be happy to share (it's not close to being fully-functional yet, but we've got a student who may be using these boards, so that might change soon). I'm also happy to try to adapt this code to more general use. With these boards and existing code, your task might be much easier than you originally thought. Also, their sales engineers are very willing to help solve problems. I don't know the prices on their boards (ours were donated), but they are excellent devices.
On stereophonic equipment, the monaural sound obtained through multiple channels will enhance your listening pleasure.
No, it's not. You don't buy digital scope to analyse perfect sinewaves. When you're looking at complex waveforms that might include single events and glitches, you need at least a sampling rate ten times your signal frequency. The only way you get your original signal back if it's been sampled at or near the Nyquist frequency is through interpolation. That might be ok for audio applications, but when you need to extract secondary information from the signal, there's just no way. Ten times is the bare minimum, and Tektronix advertise their scope bandwidth as 1/10th the sample rate.
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here
When people say 'a 40 Mhz scope',they mean a scope with which you can measure signals up to 40Mhz. Sure, nyquist says that you'll need only 80Mhz to sample a 40Mhz bandwith. But for measuring that isn't really what you want:
The reason why people say you need 10 samples is because if you sample at 80Mhz and view the difference between a 40 and 39 Mhz signal, then the 40Mhz signal will look like a perfect 40Mhz square block signal (*1), and the 39 Mhz signal will look like a 40Mhz square block signal, but where one in every fourty blocks takes twice as long. That is not a good representation of the clean 39Mhz signal at all and it is precisely the reason why you need more than 2 samples per period of the maximum frequency you want to measure with a digital oscilloscope.
Plus, if you sample a wideband signal at 80Mhz, then you'll either have a lot of aliasing problems around 30-40Mhz, or you will have to deal with the signal attenuation of the lowpass filters in the analog frontend.
*1: only if the 40Mhz is exactly in phase with the 80Mhz clock of the oscilloscope, which is never the case, hence even the 40Mhz signal will look bad.
--- Hindsight is 20/20, but walking backwards is not the answer.
A new pc-based scope with these functions, at US$495:
u res.html
- Digital Storage Oscilloscope (DSO) 2-channels 80Msamples/sec
- Logic Analyzer (LA) 16-channels
- Arbitrary Waveform Generator (AWG)
- User Programmable Power Supply (UPPS) +/- 10V
- Programmable Clock Output (1kHz - 150MHz)
http://www.dynoninstruments.com/docs/elab-080feat