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Author Topic: Best oscilloscope choice?  (Read 51716 times)

watari

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Re: Best oscilloscope choice?
« Reply #15 on: January 06, 2014, 10:18:59 PM »
BTW, the wave I expected from my Hartley circut is a sine like one, but the previous one (plugged) has a weird shape to me and i don't know if for you guys it will mean something.

Thanks!!

TinselKoala

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Re: Best oscilloscope choice?
« Reply #16 on: January 07, 2014, 08:22:14 PM »
I can't quite figure out what is going on there, but something sure doesn't seem right.

Can you show the screenshots that you get when you run the scope's "probe compensation adjustment" routine, done with and without the PC power supply plugged in? See the Manual, part 1.6, page 12.

http://www.electronicaestudio.com/docs/Hantek6022BE_Manual.pdf


You can also run the "function check", part 1.7, and the internal self calibration, 1.8, to make sure the scope itself is set up and working properly.




watari

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Re: Best oscilloscope choice?
« Reply #17 on: January 24, 2014, 06:30:47 PM »
Thanks for your advise TinselKoala.

I already did all of the things you say, but I've done them again just to double (or triple) check. I post the screen shots I took this last time.

Probe compensation: first one is plugged and the second one unplugged


watari

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Re: Best oscilloscope choice?
« Reply #18 on: January 24, 2014, 06:41:56 PM »
The fuctional check is ok. I've tried  plugged and unplugged PC and using both probes. All of them displayed the same results. According with its User's guide it has to show a wave of 2V peak to peak and a frecuecy of 1KHz aprox., and tha's what I get so everything is all right, then. Also I tried once more to calibrate being my PC unplagged.

After all of this, the same situation I explained previously remains.

Maybe the explanation does not go further than the fact that it is a cheap oscilloscope and it has its own limitations. What do you thing after all of this?

Thanks!!

TinselKoala

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Re: Best oscilloscope choice?
« Reply #19 on: January 24, 2014, 08:35:37 PM »
The calibration traces are showing that there isn't anything wrong with your scope, like a noisy AC power supply or something. I doubt if the "cheap oscilloscope limitations" have anything to do with this problem.

OK, let's figure this out.

In the post here
http://www.overunity.com/13842/best-oscilloscope-choice/msg381997/#msg381997
you are showing the traces at vastly different timebases, so I can't evaluate just what's happening.

But from your description it does sound like you are making a groundloop somehow.

Can you please post the schematic of your Hartley oscillator, including power supply, and show just where and how you are connecting the oscilloscope probes and ground references?

ayeaye

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Re: Best oscilloscope choice?
« Reply #20 on: January 26, 2015, 05:09:08 PM »
Ok, i decided to solve that oscilloscope problem for myself. This is everyones problem, for anything not changing one needs a multimeter, but the next thing one needs is an oscilloscope, to measure anything changing.

So i bought an old oscilloscope from ebay. This is a 2 channel 20mhz oscilloscope hitachi v-222, and i got it for $50 without shipping. 20mhz oscilloscopes are one of the cheapest, because they produced them the most, often cheaper than any older vintage oscilloscopes. This oscilloscope was made some time in 1980's. But such oscilloscope is not outdated, they produce and use very similar analog oscilloscopes today, and nothing essential is changed in the electronics there.

Hitachi oscilloscopes are somewhat smaller, it weighs 14 pounds or 6.5 kg, but there are even lighter ones, neither does it take much room at the corner of a table.

$50 is cheaper than most usb oscilloscope, pocket oscilloscopes or scopemeters. But such cheap ones are not more than toys, less than 5mhz real bandwidth, many other things worse. Some have only one channel and even no external triggering. But this one is a fully functional oscilloscope with full power, no need to worry about any bad shortcomings. Robust and decoupled from everything, thanks to good old transformer.

So i may shortly describe the experience i got, in buying such things. Its better to buy from sellers who have sold at least several thousand items, with a possibly higher rating. But what i considered the most important, was that there were evidence that the oscilloscope were tested. That there are pictures of test signals on the screen, and sometimes even some small faults found is rather positive than negative, because this confirms again that the item was tested. That the basic things work, this is important for two reasons. First one may not be good at repairing the oscilloscopes. But even when one can do it well, when the basic things work say after 30 years, then this confirms that it is not made of any bad series of components, and thus the electronics may work a 100 more years without repair.

When buying old oscilloscopes, what you mostly get, is only the oscilloscope itself, no probes, no power cord, no manual. But this is not a big problem, as one can get two probes for $8, the higher frequency the better, a standard computer power cord usually fits well as a power cord, and the service manuals of most of the more widespread old scopes can be downloaded from internet for free. So you get all the description, calibration instructions, and circuit diagrams.

So in what shape was my scope when it arrived? It switched on and showed two lines on the screen, so i sighed with easy, at least the power supply and the crt tube works, without these it can be unrepairable. So then i took some wires, as i have no probes yet, and connected the calibrator output (every scope has a calibrator which generates a 1khz 0.5v square signal) to the inputs of both channels. There was the first disappointment, the second channel didn't work at all.

But then, after i switched all the switches many times, absolutely everything started to work. I also tested it with an AC wall adapter output. The trigger level adjusted fine on both channels, and the trigger was completely stable. On the old scopes which have stayed unused for many years, the switches get oxidized or dirty, whatever happens because of not moving them. This is normal, after moving them many times they work well again, even no need for a contact cleaning spray. In case if that is necessary, it should be a proper one which both removes oxide and lubricates, but if really necessary, one can buy such for less than $5.

So now i have a fully working 2 channel 20mhz scope, works well and looks nice too. I see that the knobs are almost not worn at all, so likely it is not even used much. I guess most old scopes are not much used, only a small part of then had been used intensively. I'm very happy with that scope, i never regret buying it, it rather makes me feel good, and more human-like, kind of. And doesn't it look nice? :)

So i hope there was some use of what i wrote here, for anyone who also needs to buy ones first oscilloscope.

Pirate88179

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Re: Best oscilloscope choice?
« Reply #21 on: January 28, 2015, 03:44:31 AM »
Ayeaye:

Good post.  I am sure this will help a lot of folks.  I already posted about mine from ebay for $100 and I am very happy with it. (Tektronix 2213)  Mine is from the 80's also and is 20 MHz.  I am sure yours will do what mine does just fine.  $50 is a real deal.

Thanks for sharing,

Bill

ayeaye

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Re: Best oscilloscope choice?
« Reply #22 on: February 09, 2015, 04:08:13 PM »
Thank you Pirate88179 :)

As much as i know, Tektronix 2213 is 60 MHz, but i may be wrong. Tektronix 2205 is 20 MHz, as much as i know. Anyway, Tektronix started to produce the scopes with that form and design, in the beginning of 1980's, then they started to make similar ones in Japan. This is a typical 1980's scope. What concerns using it, my scope is almost identical to these Tektronix's, the knobs do everything exactly the same, calibration is similar as well, the only difference is the location of the knobs. Inside it is a bit different, Tektronix has one big board, mine has two smaller boards one on another, one of these is upside down.

Many companies made very similar scopes, so one can buy any 2 channel 20 MHz or more scope by Hitachi, Iwatsu, Kikusui, Hameg, Philips, Elenco, Tenma, Leader, Trio, Kenwood, BK Precision, Beckman, i guess i named the most widespread ones of that type of scopes. Search like "Hitachi oscilloscope", and then the cheapest. A lot to search i know, but not so terribly lot. Tektronix one cannot find that way, there are too many plugins and accessories. Tektronix also used to be somewhat more expensive, but it is high quality and its manuals are very detail and good.

In my opinion, what concerns the cheap USB oscilloscopes, then their rise time is quite good, also they tolerate at least 300 volts input voltage the same as big scopes. The rise time doesn't mean an equivalent bandwidth with the analog scope with the same rise time though. Because the analog scopes can rise and fall much faster with less vertical distance. So it is considered that the bandwidth of the digital scope is its sample rate divided by 10, but because of two channels, it has to be divided by 20. Thus a typical 40 Ms/s cheap USB scope really has a bandwidth only 2 MHz, of an equivalent analog scope. Not 20 MHz as it is said, this 20 MHz may only be true, what concerns the rise time.

The cheap USB scopes also have not quite good electronics, with too much all kind of interference. They often have a faulty software. They don't work with every USB connection, like that in virtualbox. They are coupled to the computer's ground, which some may say is not a bad thing, then others may still want to use a floating scope. If they know what they are doing, that is. And they are inconvenient, have to be connected to the computer, software started, etc.

The USB scopes they consider "cheap scopes", and thus they make them as cheap scopes. That is, they don't care about the electronics quality, or the software quality. But when buying an old scope like mine, in spite its cheap, you get a scope which once wasn't cheap and was not made or designed as cheap. So when it is made to work, it is a good scope with high quality. A serious measuring equipment, not a toy by any means. Its really sad that they don't make good low end scopes any more. Once a beginner could get some cheap one channel 10 MHz analog scope (usually with an external triggering), which was slow and had a minimal functionality, but otherwise was a good and decent scope. But today, the beginner is supposed to use a cheap USB or pocket scope, which is a lot inferior to that 10 MHz analog scope.
« Last Edit: February 09, 2015, 06:48:02 PM by ayeaye »

TinselKoala

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Re: Best oscilloscope choice?
« Reply #23 on: February 09, 2015, 05:12:58 PM »
Yep, I have a 2213a which is 60 MHz and I believe that the 2213 is the same. I paid 125 Canadian for mine from Active Surplus on Queen Street East in Toronto, lugged it home on the subway. It's a lot lighter than many old scopes so it wasn't too hard.

There is a difference in the input attenuator board, the 2213a has the same switches and attenuator/preamp board as the 2215 instead of the 2213. This caused me a little difficulty when I had to replace an input FET on one side... I had the Service Manual for the 2213 and when I opened up my scope it was different inside! But the 2215 Service Manual had the right information that I needed, including how to disassemble those complicated range switches.

The scope is excellent, I use it a lot for general purpose work since it is so easy to use, warms up fast and the delayed timebase and variable-holdoff trigger functions are great to have. Crisp and bright display too.




Pirate88179

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Re: Best oscilloscope choice?
« Reply #24 on: February 10, 2015, 01:46:25 AM »
Yes, I made an error...the 2213 is 60 mghz.  What the heck was i thinking?

Bill

MarkE

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Re: Best oscilloscope choice?
« Reply #25 on: February 10, 2015, 01:57:21 AM »
Yes, I made an error...the 2213 is 60 mghz.  What the heck was i thinking?

Bill
You should have been thinking:  That's like 40MHz free bandwidth!  Can free bandwidth be turned into free energy?

Pirate88179

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Re: Best oscilloscope choice?
« Reply #26 on: February 10, 2015, 02:48:47 AM »
You should have been thinking:  That's like 40MHz free bandwidth!  Can free bandwidth be turned into free energy?

I'll check with EMJ.  If anyone can turn free bandwidth into free energy (in his mind anyway) he can.

Bill

ayeaye

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Re: Best oscilloscope choice?
« Reply #27 on: February 10, 2015, 02:27:21 PM »
Bill,

I didn't want to emphasize that you made a mistake, i'm so sorry. I wanted to say that you were right that both the Tektronix 2200 series and my scope were made in 1980's, and were 20 MHz and 60 MHz. Many other companies made similar ones. They all had the same design, a large rectangular crt tube, and knobs to the right of it, also were lighter than the previous ones (i guess all of them should be less than 15 pounds). The knobs on all of these do all the same things, and their electronics is similar as well.

I agree that Tektronix is the best, but one can also do with a cheaper one, which is one of these scopes like mine, made by other companies, similar to Tektronix 2200 series. There are disadvantages of course, like i can nowhere get the instructions how to disassemble the switches in my scope, when paid less one certainly gets less. Yet one can get a decent working scope. My screen is 6 inches, crisp and bright as well, and all is nice and stable. A completely useful scope.

ayeaye

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Re: Best oscilloscope choice?
« Reply #28 on: February 11, 2015, 05:48:18 PM »
They sell now one in ebay that is exactly mine, hitachi v-222, for $50. If you are in America, you may get it with $15 shipping, so all you pay is $65. It is not test signal though what it shows on the screen, so this one may or may not work, but it is certainly repairable. Mine was better, on the photo there were two sine signals on the screen, this showed that both the vertical system and the triggering works. And indeed it finally appeared to be a completely working scope, with no repair.

http://www.ebay.com/itm/Hitachi-Model-V-222-20MHz-2-Channel-Oscilloscope-/171677138055?pt=LH_DefaultDomain_0&hash=item27f8c13c87

ayeaye

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Re: Best oscilloscope choice?
« Reply #29 on: March 22, 2015, 09:55:00 AM »
Old oscilloscopes are mostly sold without probes. It is possible to use wires instead, but wires don't give a good contact, cause interferences, and they cannot be pushed in too hard, to not damage the oscilloscope's connector. So i bought 100MHz oscilloscope probes from eBay for $8 with shipping. The following video is about unpacking and testing them, sorry for the mistakes which i made, please read the description.

https://archive.org/details/probes_201503