Author Topic: Least expensive but reliable used-market scope with at least 1 GHz?  (Read 29526 times)

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Offline EV

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Re: Least expensive but reliable used-market scope with at least 1 GHz?
« Reply #75 on: November 01, 2015, 11:17:24 am »
Here is the same picture with TEK R7633 scope. Store button is on.
20 dB attenuator, internal triggering and random sampling.
 

Offline Wuerstchenhund

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Re: Least expensive but reliable used-market scope with at least 1 GHz?
« Reply #76 on: November 01, 2015, 11:29:41 am »
I agree that the Tek/HP saying had it's best merit back in the analog days.  While I still think highly of Tek scopes (trust me, you don't have to tell me about why LeCroy is better, I read your posts) it's clear that Tek's heydays didn't fully traverse the A to D revolution; the dominance they enjoyed in the analog days declined but I still respect them and have a fondness for their MSO/MDO gear.  I know, I know LeCroy is better - I can see you reaching for the keyboard :)

If they are better is dependent on what you do (i.e. if you need more than 1.5GHz bandwidth then these old LeCroys are not much use, and you'd have to look at the successor WavePro 900 which goes to 2GHz or scopes from other brands anyways), but I'd say they are the most versatile scopes of that era due to the large memory, the fast sample rates and the sheer amount of analysis and measurement options. If you look at digital scopes from other manufacturers of that time you'll see that they are pretty basic in comparison.

Having said that, HP has made some really good digital scopes, too, i.e. if you needed a scope for TDR measurements and a very high bandwidth at a rock-bottom price then a sampling scope like the HP 541xx/547xx is hard to beat.

As to Tek digital scopes from that era, well, I can't see why someone would consider them over the other available alternatives unless you're a fan of Tek gear. They have small screens (and for some reason the color versions come with a monochrome tube with some LCD shutter mask to create color instead of using a color tube), a horrible UI, and very few advanced options. Some come with deep memory as option but for some reason the high bandwidth variants (TDS600) only got a ridiculous 15kpts (the TDS694C that has been mentioned before in this thread can at least be upgraded to 120k but this is still pretty poor) which noticably limits the benefit their high sample can bring. As mentioned before the older TDS also suffer from capacitor plaugue. And on top of it there is the price premium simply for being a Tek.

If you want a digital scope from the '90s then I'd focus on HP/Agilent and LeCroy.

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The reason for the thread is pretty much what I mentioned to dr.diesel on the first page of the thread - what started this inquiry was simply a desire to achieve better rise time measurements (but so as not close off other possible improvements I didn't want to constrain a wider discussion of what folks think might be a really good 1GHz scope in general - ie, a scope with other functionality and performance improvements beyond just improved risetimes, while trying to keep the price down).  Said differently, for this endeavor maximizing risetime performance is the base case and everything else is the value-added case. 

I see. That changes things a bit.

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I have 4 scopes.  (According to the recent thread underway I'm 16 scopes away from par if par is 20; so I have a long way to go to get to par much less a birdie or an eagle, in golf-speak).

Well, you're better than me then because I only have 2.5 scopes (two LeCroys and one scope from a company that shall not be named who seems to dislike private ebay ssales of their gear so has them taken down for trademark infringement and who doesn't bother to complete the firmware for that scope, so due to the half-done firmware I don't count it as full scope)  ;)

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Most of what I do (which is just trying to learn through small projects and experimenting) can be done with 100MHz or less - so that can be done on my Rigol (70MHz) or Tek 2247A (100MHz).  I also have a 2465B which is spec'd at 400MHz but does somewhat better.  Lastly, I have a Tek 7000 which is spec'd to 500MHz but my amplifier plugins are only spec'd for 200MHz; I'm on the lookout for a 500MHz 7A29.  In the meantime I became fascinated with the Jim Williams generator (now I have two of those, not much in test equipment land seems to hold steady at quantity 1).  The JW generators showed my scopes couldn't keep up with the fast pulse gens.  So, I started thinking how much bandwidth do I need and what could I maybe afford to see hundreds of picoseconds risetimes, or better yet, maybe tens of picoseconds risetimes.  (The 2467B is spec'd at 875ps and does somewhat better - but going faster seems to be an addiction for no good reason.) 

So, this all led to researching 1GHz scopes (an arbitrary number but a notable threshold, perhaps).  That led to the suggestions here to investigate the Tek 7000 sampling plug-ins.  Somehow even though I had the Tek 7000 I wasn't at all on top of the sampling capabilities.  I've found a 7S11 with a S-1 (only good to 350ps but that's 525ps faster than the 2467B); so I think for now I just need a 7T11 and I'm sub-500ps risetime ready.  With a S-4 I'd be down to 25ps.  There is no good reason to do this except that a) it's fascinating to think about looking at signals operating in the trillionths of a second, and b) as Howardlong mentioned (I'm paraphrasing) the more you can visualize signals the more insight/learning you can gain.  There is no payoff other than curiosity addressed.

Well, in this case I agree that you're probably best served with the 7000 and its sampling plugins, which should be more cost-effective than buying some 1GHz scope from the '90s (which aren't really that cheap, and quite often going for a bit newer and more capable model doesn't add much to the price tag).
« Last Edit: November 01, 2015, 01:36:19 pm by Wuerstchenhund »
 

Offline Electro Fan

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Re: Least expensive but reliable used-market scope with at least 1 GHz?
« Reply #77 on: November 01, 2015, 12:29:39 pm »
"The 284 looks like a very nice piece of equipment but it is out of my justifiable budget.  "

So what is your budget and what country are you in?

I have 2 pulse generators that are spec'd with rise times faster than my scopes can see so adding a 3rd at any price doesn't seem to make sense.  Maybe I'm not seeing the good deals on 284s but on the U.S. eBay market so-so condition 284s go for about $400 - for about the same total amount or less you can find all three sampling plugin components (7S11/S-X/7T11).
 

Online KE5FX

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Re: Least expensive but reliable used-market scope with at least 1 GHz?
« Reply #78 on: November 01, 2015, 08:13:26 pm »
As to Tek digital scopes from that era, well, I can't see why someone would consider them over the other available alternatives unless you're a fan of Tek gear. They have small screens (and for some reason the color versions come with a monochrome tube with some LCD shutter mask to create color instead of using a color tube), a horrible UI, and very few advanced options. Some come with deep memory as option but for some reason the high bandwidth variants (TDS600) only got a ridiculous 15kpts (the TDS694C that has been mentioned before in this thread can at least be upgraded to 120k but this is still pretty poor) which noticably limits the benefit their high sample can bring.

The 120K record length limitation isn't all that "poor" when you consider that it's used for single-shot acquisition at 10 GS/s.  The 694C was already the priciest scope in the entire Tek catalog during the years when it was offered (2000-2003-ish), and it's not clear who would have been willing to pay for more acquisition memory.  They had to be using either CCDs or interleaved banks of the fastest SRAM available, possibly both.

It's worth asking what other real-time DSOs will get you to 3 GHz in the sub-$2000 range.  I'm not familiar with LeCroy's offerings; do they have a 694C competitor that people in that market should be looking at?  At the time I was shopping for mine, the next step up would have been an HP 54854A at more than twice the price.
« Last Edit: November 01, 2015, 08:35:03 pm by KE5FX »
 

Online nctnico

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Re: Least expensive but reliable used-market scope with at least 1 GHz?
« Reply #79 on: November 01, 2015, 09:26:21 pm »
The TDS694C still goes for quite a lot of money. Unfortunately one of it's problems is the trigger chip overheating and dying. Ofcourse that chip is made from unobtainium. OTOH: you could get lucky buying a replacement chip. A couple of weeks ago I bought a scope which had some custom ASICs which needed replacement and much to my surprise I could buy the chips for a reasonable price... Anyway: it is worth investigation the repair options before buying a TDS694C. Besides that there is also the Tektronix TDS820 (6GHz sampling scope) with the usual capacitor plague.
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Online KE5FX

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Re: Least expensive but reliable used-market scope with at least 1 GHz?
« Reply #80 on: November 01, 2015, 11:34:39 pm »
The TDS694C still goes for quite a lot of money. Unfortunately one of it's problems is the trigger chip overheating and dying. Ofcourse that chip is made from unobtainium. OTOH: you could get lucky buying a replacement chip. A couple of weeks ago I bought a scope which had some custom ASICs which needed replacement and much to my surprise I could buy the chips for a reasonable price... Anyway: it is worth investigation the repair options before buying a TDS694C. Besides that there is also the Tektronix TDS820 (6GHz sampling scope) with the usual capacitor plague.

It turns out that those scopes actually had spare trigger chips on the board.  They were connected to power, but apparently never used for anything. 

I had a spare TDS 694C whose main timebase wouldn't trigger, and a friend who works in the T&M business was able to repair it by moving two chips.  (Both of my original ones were bad.)  I didn't believe him at first, but I haven't been able to find any missing trigger functionality on this scope, so apparently he knew what he was talking about.  Crazy stuff!

 

Online Howardlong

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Re: Least expensive but reliable used-market scope with at least 1 GHz?
« Reply #81 on: November 02, 2015, 08:30:15 am »
Here is the same picture with TEK R7633 scope. Store button is on.
20 dB attenuator, internal triggering and random sampling.

Interesting, I don't have any knowledge of the Tek 7000 series, how does the internal triggering work? It looks like there is some kind of delay after the trigger, or is there something clever going on? Like a time machine? ;-)
 

Offline EV

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Re: Least expensive but reliable used-market scope with at least 1 GHz?
« Reply #82 on: November 02, 2015, 11:20:34 am »
Here is the same picture with TEK R7633 scope. Store button is on.
20 dB attenuator, internal triggering and random sampling.

Interesting, I don't have any knowledge of the Tek 7000 series, how does the internal triggering work? It looks like there is some kind of delay after the trigger, or is there something clever going on? Like a time machine? ;-)

I dont know how random samplig works. I am not professional on these things. This kind not pretriggered pulse signal can not be seen with fast time bases using sequential sampling.
 

Offline EV

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Re: Least expensive but reliable used-market scope with at least 1 GHz?
« Reply #83 on: November 02, 2015, 11:52:01 am »
Here is a new picture from R7633 with storage level adjusted bigger.
 

Offline Wuerstchenhund

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Re: Least expensive but reliable used-market scope with at least 1 GHz?
« Reply #84 on: November 02, 2015, 05:51:04 pm »
The 120K record length limitation isn't all that "poor" when you consider that it's used for single-shot acquisition at 10 GS/s.

It is, because the tiny sample memory means that the period you can capture at full sample rate is ridiculously small (12us with the optional 120kpts "large" memory option if my math is correct). It also means that to capture longer periods the sample rate will have to drop noticeably so that the tiny memory covers the whole period, i.e. the sample rate already drops if you extend the timebase beyond 1us/div.

120k points would be considered poor for a scope with slower sample speed already, and that is even more true for a fast sampler like the TDS694C. The TDS600 Series is pretty badly balanced, which makes them a poor choice for pretty much anything except some niche tasks, and together with the other issues (i.e. the trigger IC overheating nctnico mentioned, which is simply poor design, or the failing LCD shutter) makes the TDS600 a pretty poor choice.

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The 694C was already the priciest scope in the entire Tek catalog during the years when it was offered (2000-2003-ish), and it's not clear who would have been willing to pay for more acquisition memory.

Pretty much everyone who wanted to capture longer periods or make use of long memory for sequence mode. Remember that 120k would already be poor on say a 2GSa/s scope, and the higher sample rate of the TDS694C (which equals to a larger amount of data) only makes matters worse.

In addition, the TDS694C wasn't exactly cheap when it came out, it did cost the same (or even more) than comparable scopes from other manufacturers at that time which all came with more sample memory.

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It's worth asking what other real-time DSOs will get you to 3 GHz in the sub-$2000 range.

Sub-$2000? Not sure about that, most of the TDS694C seem to go for closer to $2500 - $3500 which isn't exactly cheap. $2000 pretty much only buys you "untested" (yeah, right) or broken ones. That's a lot of money for such a an old and (aside from bandwidth and max sample rate) pretty basic scope.

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I'm not familiar with LeCroy's offerings; do they have a 694C competitor that people in that market should be looking at?

Well, it depends on where the priorities are. In the age and somewhat similar price range of the TDS694C there are essentially three LeCroy scopes, the older WavePro 960, the successor WavePro 7300, the WaveMaster 8400, and the WaveRunner 6200.

The WavePro 960 is a 2GHz scope (50ohms/1M switchable inputs) which offers 16GSa/s and up to 64Mpts memory (standard is 1M), and which came out around the same time as the TDS694C (end 1999/early 2000). The 950 is the largest model (there's also the 1GHz 950 and the 500MHz 940) and like other LeCroy scopes it comes with a pretty long of available options which includes advanced triggers, advanced math and FFT, Jitter and Timing Analysis and lots more, however it doesn't do serial decode. But it does come with a nice large 10.4" TFT display (no CRT), it boots quickly, and the UI is pretty straightforward. The WP900 was the last of LeCroy's VxWorks based upper high end scope, it was manufactured by Iwatsu, and has shown to be rock-solid (the only weak spot is the plastics front cover which tends to crack in the lower right corner, however a replacement can be bought for $20 or so).

With some patience you can find working WavePro 960s for below $2k, but they can often go for between $2k and $3k (so roughly the same price range as the TDS694C).

If 3GHz is required then one would be looking at the successor WavePro 7300 (non-A model) which came out around late 2001/early 2002. It's more expensive than the TDS684C but it's also a completely different generation of scope i.e. 20GSa/s with up to 72M memory and touch screen which runs Windows 2000 (can and should be upgraded to XP) for which a huge range of options is available, including serial decode for a wide range of common and less common/niche/obscure protocols. As the older WavePro 950 these scopes are very reliable (especially under Windows XP) if using the latest software (these scopes are still supported with updates!) and not messing with Windows settings. Aside from the front cover (which is the same as for the WP900) the only real weak spot is the hard drive, however this is a standard IDE drive that can be replaced easily. Otherwise these scopes are solid like a rock. As with the WavePro 900, the WP7000 Series does have 50ohms/1M switchable inputs.

Like all LeCroy mid-range and high-end scopes since the 9300 Series both WavePro 900 and WavePro 7000 use the LeCroy ProBus interface for which the second hand market often has a good selection of reasonably priced active probes.

However, there's also the larger WaveMaster 8000 Series which is basically the higher bandwidth variant of the WavePro 7000. The WM8000 Series starts with the WM8400 with 4GHz bandwidth (WM8500: 5GHz; WM8600: 6Ghz) and comes with 50ohms inputs with ProLink interface. Aside the bandwidth and the front end the scope is pretty similar to the WP7000, with up to 20GSa/s sample rate (however, standard memory is 4M/8M, with up to 100M). Because the WM8k comes with a 50ohms only input it can often be had for less than a WavePro 7000. I've seen a WM8500 go for approx $3500.

Last but not least there's also the WaveRunner 6200, 1 2GHz scope with 10GSa/s and 2M standard (up to 24M). As the Wavepro 7000 and WaveMaster 8000 this is a Windows 2000 based scope which comes with a wide range of options including serial decode, although the list is somewhat shorter than for the WP7k/WM8k. The LCD screen is smaller (8.4"), too. As with the other scopes, the WR6000 is a very reliable scope without any known flaws (again aside from the hard drive, but hard drives are essentially consumables anyways). WR6200s are pretty rare but I've seen them go for roughly the same money as a WavePro 960.

None of these scopes suffer from overheating, capacitor plague or any other major flaw that can be found in the old TDS Series. In addition, unlike the old Tek scopes even the old WavePro 900 can be sent to LeCroy for repair, and spare parts are also still available. Tek doesn't even service many scopes that are much younger.

However, if price matters most and one can live with 2GHz bandwidth then I'd say even an Agilent 54720D with 54722A (2Ghz 8GSa/s plugin with 256k memory) is a better choice than a TDS694C, plus like the LeCroys above it also doesn't suffer from overheating ICs. And the 54720D/54722A combination should be even less expensive than the LeCroy scopes above or a TDS694C.

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At the time I was shopping for mine, the next step up would have been an HP 54854A at more than twice the price.

Understandable since the is a much more modern scope than the TDS694C. The 54854A offers 4Ghz bandwidth, up to 20GSa/s sample rate, double the memory as standard (262k) than the TDS694C has when fitted with "long" memory, can have up to 32M sample memory, offers a range of advanced options including serial decode, comes with an LCD screen, and is overall a much better balanced scope than the TDS694C.
« Last Edit: November 02, 2015, 07:20:50 pm by Wuerstchenhund »
 

Online edavid

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Re: Least expensive but reliable used-market scope with at least 1 GHz?
« Reply #85 on: November 02, 2015, 06:06:22 pm »
Sub-$2000? Not sure about that, most of the TDS694C seem to go for closer to $2500 - $3500 which isn't exactly cheap. $2000 pretty much only buys you "untested" (yeah, right) or broken ones. That's a lot of money for such a an old and (aside from bandwidth and max sample rate) pretty basic scope.

Here's a perfectly nice one that sold for $1263:

http://www.ebay.com/itm/Tektronix-TDS694C-3GHz-4-Channel-Oscilloscope-Options-1M-HD-/131589284202

I've noticed that you like to overstate the price of used Tek scopes, and understate used LeCroys  :-//
 

Offline Jwalling

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Re: Least expensive but reliable used-market scope with at least 1 GHz?
« Reply #86 on: November 02, 2015, 06:13:33 pm »
The TDS694C still goes for quite a lot of money. Unfortunately one of it's problems is the trigger chip overheating and dying. Ofcourse that chip is made from unobtainium. OTOH: you could get lucky buying a replacement chip. A couple of weeks ago I bought a scope which had some custom ASICs which needed replacement and much to my surprise I could buy the chips for a reasonable price... Anyway: it is worth investigation the repair options before buying a TDS694C. Besides that there is also the Tektronix TDS820 (6GHz sampling scope) with the usual capacitor plague.

It turns out that those scopes actually had spare trigger chips on the board.  They were connected to power, but apparently never used for anything. 

I had a spare TDS 694C whose main timebase wouldn't trigger, and a friend who works in the T&M business was able to repair it by moving two chips.  (Both of my original ones were bad.)  I didn't believe him at first, but I haven't been able to find any missing trigger functionality on this scope, so apparently he knew what he was talking about.  Crazy stuff!



Hi John,

Wow, I didn't know that.  :-+ Would you happen to have a picture of the complete board?
Were the extra trigger chips completely soldered down including the large pad under the chip?

Jay (Sold you your working TDS694C)
Jay

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Offline Wuerstchenhund

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Re: Least expensive but reliable used-market scope with at least 1 GHz?
« Reply #87 on: November 02, 2015, 06:14:06 pm »
Sub-$2000? Not sure about that, most of the TDS694C seem to go for closer to $2500 - $3500 which isn't exactly cheap. $2000 pretty much only buys you "untested" (yeah, right) or broken ones. That's a lot of money for such a an old and (aside from bandwidth and max sample rate) pretty basic scope.

Here's a perfectly nice one that sold for $1263:

http://www.ebay.com/itm/Tektronix-TDS694C-3GHz-4-Channel-Oscilloscope-Options-1M-HD-/131589284202

Great. Not all TDS694C sell at just $1263, though:
http://www.ebay.com/itm/Tektronix-TDS694C-Color-4-Channel-Oscilloscope-3GHz-10GSa-s-13-1F-HD-1M-2F-/301739835878?hash=item46411881e6:g:mhQAAOSwQPlV9dqu

http://www.ebay.com/itm/Tektronix-TDS694C-Digital-Oscilloscope-4Ch-3Ghz-10Gs-s-Options-/311439784843?hash=item488341fb8b:g:V0EAAOSwyQtV7D5O

Quote
I've noticed that you like to overstate the price of used Tek scopes, and understate used LeCroys  :-//

Not really. I just am long enoughj on ebay to know that prices can pretty much vary a lot depending on time of the year, when an auction ends, description, quality of pictures, and a ton of other parameters, and that some variations don't mean that the same item will always sell at the same price.
 

Offline Jwalling

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Re: Least expensive but reliable used-market scope with at least 1 GHz?
« Reply #88 on: November 02, 2015, 06:28:48 pm »
Not really. I just am long enoughj on ebay to know that prices can pretty much vary a lot depending on time of the year, when an auction ends, description, quality of pictures, and a ton of other parameters, and that some variations don't mean that the same item will always sell at the same price.

And one of the most important in auction-style listings: Just how bad someone wants it!

Jay
Jay

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Online edavid

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Re: Least expensive but reliable used-market scope with at least 1 GHz?
« Reply #89 on: November 02, 2015, 06:40:22 pm »
Sub-$2000? Not sure about that, most of the TDS694C seem to go for closer to $2500 - $3500 which isn't exactly cheap. $2000 pretty much only buys you "untested" (yeah, right) or broken ones. That's a lot of money for such a an old and (aside from bandwidth and max sample rate) pretty basic scope.

Here's a perfectly nice one that sold for $1263:

http://www.ebay.com/itm/Tektronix-TDS694C-3GHz-4-Channel-Oscilloscope-Options-1M-HD-/131589284202

Great. Not all TDS694C sell at just $1263, though:
http://www.ebay.com/itm/Tektronix-TDS694C-Color-4-Channel-Oscilloscope-3GHz-10GSa-s-13-1F-HD-1M-2F-/301739835878?hash=item46411881e6:g:mhQAAOSwQPlV9dqu

http://www.ebay.com/itm/Tektronix-TDS694C-Digital-Oscilloscope-4Ch-3Ghz-10Gs-s-Options-/311439784843?hash=item488341fb8b:g:V0EAAOSwyQtV7D5O

So by pointing out that the 2 of the highest priced sold listings went for $2200 and $2400, you're agreeing that your statement "most of the TDS694C seem to go for closer to $2500 - $3500" is incorrect?
 

Offline Wuerstchenhund

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Re: Least expensive but reliable used-market scope with at least 1 GHz?
« Reply #90 on: November 02, 2015, 07:05:17 pm »
So by pointing out that the 2 of the highest priced sold listings went for $2200 and $2400, you're agreeing that your statement "most of the TDS694C seem to go for closer to $2500 - $3500" is incorrect?

It's not incorrect. It's probably news to you but to get a feeling for the usual going rate on ebay you need a longer period than the 90 days that you can backtrack on ebay searches. Especially when this timespan includes the time of the year where people tend to spend less so they can spend a bit more for Xmas. I buy a lot of test gear, and monitor prices pretty closely.

Some time ago a Rohde & Schwarz FSU26 spectrum analyzer with options sold in an auction for approx £1000 when the same analyzer usually sells for £6k+ (unfortunately I missed that one). However it would be silly to assume that the value of an FSU26 is just £1000.

The winner of that TDS694C for $1263 was lucky, and so were the other two (probably to an lesser extend, but still) who got their TDS694C for below $2.5k. It doesn't necessarily mean if you wanted one that you'd get one for a similar price.

Not really. I just am long enoughj on ebay to know that prices can pretty much vary a lot depending on time of the year, when an auction ends, description, quality of pictures, and a ton of other parameters, and that some variations don't mean that the same item will always sell at the same price.

And one of the most important in auction-style listings: Just how bad someone wants it!

Exactly. My experience is that unless an item is really sought after (i.e. Apple stuff) and has lots of interest then an auction will often rake in less money than a (somewhat realistic) Buy-It-Now price. But considering the amount of overpriced gear on offer I guess "realistic" means different things for sellers and buyers  ;)
 

Online nctnico

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Re: Least expensive but reliable used-market scope with at least 1 GHz?
« Reply #91 on: November 02, 2015, 08:00:38 pm »
Let's just say that you can get really good deals on Ebay every now and then. It just depends on how badly you need it. I have several searches running and sometimes something interesting pops up for the right price.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Online KE5FX

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Re: Least expensive but reliable used-market scope with at least 1 GHz?
« Reply #92 on: November 02, 2015, 08:52:19 pm »
Hi John,

Wow, I didn't know that.  :-+ Would you happen to have a picture of the complete board?
Were the extra trigger chips completely soldered down including the large pad under the chip?

Jay (Sold you your working TDS694C)

No, that's the only photo I took -- the entire board is pretty large.  The spare chips are soldered down just like the others, pad included, so you need a hot-air station with a preheater to rework them safely. 

I still can't wrap my head around the idea that Tektronix populated the board with expensive nonfunctional parts.  It might be understandable if there were another variant with slightly different specs that needed all four parts, or if an option that took advantage of them had been offered for sale, but neither seems to have been the case.  (I'm assuming the 794D used a different acquisition board, being a DPO.)

Well, it depends on where the priorities are. In the age and somewhat similar price range of the TDS694C there are essentially three LeCroy scopes, the older WavePro 960, the successor WavePro 7300, the WaveMaster 8400, and the WaveRunner 6200...

Good info -- the 960 looks like a solid competitor in most respects.  The 694C sacrifices heavily at the altar of bandwidth, and it does show up in the real-world price. 

I think of the 694C as sort of a spiritual successor to the 519, where you paid a king's ransom for a 2-division CRT driven by a 4CX250 and not much else.   I wouldn't defend it as one of the all-time great general purpose scopes, but the point stands: if you need 3 GHz for $1500 or so, there are currently no alternatives. 

LeCroy plays silly games of their own -- notice how the sampling rate of the 2 GHz 960 goes down to 4 GS/s if you enable all four channels.  That means it can no longer be considered a real-time DSO.  I don't know what I'd call it, but it wouldn't be polite.  :P  On the other hand, the Tek maintains an honest (if inadequate) 10 GS/s with all four channels turned on.  They get a lot of credit for that in my book.

« Last Edit: November 02, 2015, 08:54:31 pm by KE5FX »
 

Online Howardlong

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Re: Least expensive but reliable used-market scope with at least 1 GHz?
« Reply #93 on: November 02, 2015, 09:10:41 pm »
Folks

One of those QuickStart8 DPO demo boards on eBay turned up today, here's how the rising edge looks on the 54120B/54121A. The board generates a 24MHz square wave at its Fast Rise signal, so easy to pre-trigger on.

The setup is:

33" SMA-SMA Radiall interconnect 0.37dB/ft @ 18GHz
HP 11742A SMA inline blocking capacitor
Weinschel 1515-1 18GHz SMA resistive power splitter
2 x 10.5" SMA-SMA Radiall interconnects, 0.89dB/ft @ 18GHz, to the Ch1 and trigger inputs.

The close-in second picture shows a slightly longer rise time as the entire preshoot is not taken into account.





 

Offline Electro Fan

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Re: Least expensive but reliable used-market scope with at least 1 GHz?
« Reply #94 on: November 02, 2015, 09:49:47 pm »
One of those QuickStart8 DPO demo boards on eBay turned up today, here's how the rising edge looks on the 54120B/54121A. The board generates a 24MHz square wave at its Fast Rise signal, so easy to pre-trigger on.

Roger that

Since we've seen your scope get well below 100ps we can be pretty sure that the ~152ps risetime is the performance of the QuickStart8 demo board - which is in line with Tek's quote spec of <200ps.

On the 2467B it produces about a 720ps rise time (maybe you can see if you get a similar reading on your 2467B).  I'm looking forward to seeing what the measurement will be on the Tek 7000 sampling system - just need another part...
 

Offline Wuerstchenhund

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Re: Least expensive but reliable used-market scope with at least 1 GHz?
« Reply #95 on: November 03, 2015, 10:31:30 am »
I think of the 694C as sort of a spiritual successor to the 519, where you paid a king's ransom for a 2-division CRT driven by a 4CX250 and not much else.   I wouldn't defend it as one of the all-time great general purpose scopes, but the point stands: if you need 3 GHz for $1500 or so, there are currently no alternatives. 

If you can get one at $1500, yes.

Quote
LeCroy plays silly games of their own -- notice how the sampling rate of the 2 GHz 960 goes down to 4 GS/s if you enable all four channels.  That means it can no longer be considered a real-time DSO.  I don't know what I'd call it, but it wouldn't be polite.  :P

It's true that with four channels enabled the WP960 sampling rate goes to 4GSa/s only, but at 2GHz bandwidth that still meets Nyquist for a signal up to 2GHz.

Lets have a closer look at how both scopes perform at various timebase settings:

Tektronix TDS694C with standard (30k) and "long" (120k) memory
Timebase SettingSample Rate (std memory)Frequency limit (fsample/2) (std memory)Sample Rate (long memory)Frequency limit (fsample/2) ("long" memory)
10ns/div10GS/s3GHz (bw limit)10GS/s3GHz (bw limit)
20ns/div10GS/s3GHz (bw limit)10GS/s3GHz (bw limit)
30ns/div10GS/s3GHz (bw limit)10GS/s3GHz (bw limit)
50ns/div10GS/s3GHz (bw limit)10GS/s3GHz (bw limit)
100ns/div10GS/s3GHz (bw limit)10GS/s3GHz (bw limit)
200ns/div10GS/s3GHz (bw limit)10GS/s3GHz (bw limit)
300ns/div10GS/s3GHz (bw limit)10GS/s3GHz (bw limit)
500ns/div5GS/s2.5GHz10GS/s3GHz (bw limit)
1us/div2.5GS/s1.25GHz10GS/s3GHz (bw limit)
2us/div2.5GS/s1.25GHz5GS/s2.5GHz
3us/div1GS/s500MHz2.5GS/s1.25GHz
5us/div500MS/s250MHz2.5GS/s1.25GHz
10us/div250MS/s125MHz1GS/s500MHz
20us/div125MS/s62.5MHz500MS/s250MHz
30us/div100MS/s50MHz250MS/s125MHz

The table clearly shows that the small memory causes huge 3GHz bandwidth and the fast 10GSa/s sample rate to drop dramatically beyond 1us/div (long memory) or even 200ns/div (std memory), and with it the useful bandwidth, i.e. at 10us it's essentially just a 500MHz (long memory) or even just a 125MHz (std memory) scope.

Lets see how the WP960 performs:

LeCroy WavePro 960 quad channel with standard (250k) and long (16M) memory
Timebase SettingSample Rate (std memory)Frequency limit (fsample/2) (std memory)Sample Rate (long memory)Frequency limit (fsample/2) (long memory)
10ns/div4GS/s2GHz (bw limit)4GS/s2GHz (bw limit)
20ns/div4GS/s2GHz (bw limit)4GS/s2GHz (bw limit)
30ns/div4GS/s2GHz (bw limit)4GS/s2GHz (bw limit)
50ns/div4GS/s2GHz (bw limit)4GS/s2GHz (bw limit)
100ns/div4GS/s2GHz (bw limit)4GS/s2GHz (bw limit)
200ns/div4GS/s2GHz (bw limit)4GS/s2GHz (bw limit)
300ns/div4GS/s2GHz (bw limit)4GS/s2GHz (bw limit)
500ns/div4GS/s2GHz (bw limit)4GS/s2GHz (bw limit)
1us/div4GS/s2GHz (bw limit)4GS/s2GHz (bw limit)
2us/div4GS/s2GHz (bw limit)4GS/s2GHz (bw limit)
3us/div4GS/s2GHz (bw limit)4GS/s2GHz (bw limit)
5us/div4GS/s2GHz (bw limit)4GS/s2GHz (bw limit)
10us/div2GS/s1GHz4GS/s2GHz (bw limit)
20us/div1GS/s500MHz4GS/s2GHz (bw limit)
30us/div1GS/s500MHz4GS/s2GHz (bw limit)
50us/div500MS/s250MHz4GS/s2GHz (bw limit)
100us/div250MS/s125MHz4GS/s2GHz (bw limit)
200us/div125MS/s62.5MHz4GS/s2GHz (bw limit)
300us/div50MS/s25MHz4GS/s2GHz (bw limit)
500us/div50MS/s25MHz2GS/s1GHz
1ms/div25MS/s12.5MHz1GS/s500MHz

The initial bandwidth of the WP960 is of course lower (2GHz vs 3GHz), however the WP960 maintains a fast sample rate for much longer than the TDS694C. Even with the reduced sample rate in 4 channel mode the WP960 with  deep memory still captures at full analog bandwidth where a fully spec'd TDS694C only captures less than 100MHz. And this performance distance only gets larger when only two or a single channel is needed as the WP960 can combine sampling and memory sizes.

This also pretty much shows that a scope's performance can't be judged just by looking at two of the main parameters (analog bandwidth and sample rate). There's a lot more to it.

Quote
On the other hand, the Tek maintains an honest (if inadequate) 10 GS/s with all four channels turned on.  They get a lot of credit for that in my book.

I agree, the sample rate is pretty good, but as the tables above shows its  advantage is mostly negated by the ridiculously small memory.

The other question is what one actually wants to do with the scope. High bandwidth scopes are rarely used to look at a 3Ghz sine wave, they are used to look at high bandwidth transmission systems (i.e. fast data buses), fast pulse trains or similar stuff, and for that I'm sorry to say the TDS694C is pretty useless, mostly due to its small sample memory (and the lack of analysis capabilities doesn't help, either).
 

Online nctnico

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Re: Least expensive but reliable used-market scope with at least 1 GHz?
« Reply #96 on: November 03, 2015, 11:45:42 am »
If you take peak-detect into account the TDS694C doesn't run out of breath that quickly. So even at lower sweep rates you'll still have full bandwidth to find glitches.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline Wuerstchenhund

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Re: Least expensive but reliable used-market scope with at least 1 GHz?
« Reply #97 on: November 03, 2015, 12:01:45 pm »
If you take peak-detect into account the TDS694C doesn't run out of breath that quickly. So even at lower sweep rates you'll still have full bandwidth to find glitches.

True, but Peak Detect is essentially a crutch to compensate for the lack of sample memory. It also comes with its own problems, i.e. the loss of timing information in the samples and the introduction of noticeable distortion (noise) into the waveform, which makes it useless for anything that requires a true waveform representation (i.e. signal analysis/FFT).

I'm doing lots of glitch finding in high speed circuits, and I can't even remember when was the last time that I've used Peak Detect. Personally, I'd take a deep memory scope over a small memory scope with PD any day.
« Last Edit: November 03, 2015, 12:15:36 pm by Wuerstchenhund »
 

Online nctnico

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Re: Least expensive but reliable used-market scope with at least 1 GHz?
« Reply #98 on: November 03, 2015, 12:20:44 pm »
But if you really need/want 3GHz then the TDS694C is the cheapest choice out there when it comes to a realtime sampling scope which can also be used as a general purpose scope.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Online KE5FX

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Re: Least expensive but reliable used-market scope with at least 1 GHz?
« Reply #99 on: November 03, 2015, 10:30:23 pm »
If you take peak-detect into account the TDS694C doesn't run out of breath that quickly. So even at lower sweep rates you'll still have full bandwidth to find glitches.

True, but Peak Detect is essentially a crutch to compensate for the lack of sample memory. It also comes with its own problems, i.e. the loss of timing information in the samples and the introduction of noticeable distortion (noise) into the waveform, which makes it useless for anything that requires a true waveform representation (i.e. signal analysis/FFT).

I'm doing lots of glitch finding in high speed circuits, and I can't even remember when was the last time that I've used Peak Detect. Personally, I'd take a deep memory scope over a small memory scope with PD any day.

Yeah, absolutely, in the general case.   What the 694C is primarily good for is looking for ringing/overshoot issues -- impedance matching, in other words -- in the time domain.  If you need to look at a whole Gig-E or USB packet, you're likely to want more memory.  But if you need to evaluate PCB trace terminations or determine where they're needed, it's a great tool.  Physical-layer SI problems in the sub-300 MHz regime can't hide from a 10 GS/s scope with FET probes.

For most other 500 MHz+ use cases, a spectrum analyzer is more likely to be my weapon of choice.  If I wanted to measure fast risetimes of a repetitive waveform, like the OP of this thread, I'd be more inclined to look at its comb spectrum.  Actually I probably use the FET probes with an SA more often than I use them with the 694C. 

The thing about a scope is, no matter how fast it is, you always want something faster.  Same with memory depth.  Moving to the frequency domain can get you out of that trap.
 


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