Nice, older DSO advice

[0culus]

I'm just going to try to distill down some of my scattered thoughts here. TL;DR I want to get a nice DSO for my personal lab, this year, to provide capability that my collection of CROs don't provide. Use case for the DSO will primarily be working with reasonably high speed (say ~100 MHz) digital logic and FPGA projects. I already have a benchtop logic analyzer, so I don't really need mixed signal.

Budget-wise, short of winning a contest, a brand new high end DSO is pretty much right out. Way too expensive. So the next best thing is to do what I normally do and find something that's a bit older. I believe in purchasing the best tools that you can afford, thus I am looking for professional quality older used stuff from top brands. Sorry, tautech.    Let's say that my budget for the purposes of discussion is $5000.

Keysight and Tek are standard brands one thinks of, but honestly I'm very interested in looking at LeCroy and R&S as well. I found this, for instance: eBay auction: #232562487402


Thoughts and advice are all appreciated. Again, not making this purchase soon but trying to learn as much as possible before I do so I'm ready. 

[Kosmic]

Pssstt you can "unlock" all software features with most of the older Lecroy models. If someone is asking I didn't told you 

https://www.eevblog.com/forum/testgear/lecroy-options-recovery/

And the software package on Lecroy oscilloscope is normally really interesting. Even the older one.

[Mr Nutts]

Keysight and Tek are standard brands one thinks of, but honestly I'm very interested in looking at LeCroy and R&S as well. I found this, for instance: eBay auction: #232562487402

Ignore Tek, they had great analog scopes but the DSOs were very poor

If you want to learn about Lecroy then there are lots of very good posts by former (now banned) member "Wuerstchenhund" (hope I spellt that right) who knows more about scopes than anyone else I have met

I have a Lecroy LT574 which is the previous model from the one in your ebay link. With options unlocked it can do so much that I often still find something new

Agilent/Keysight scopes are very nice, and there are some inexpensive options like the 54622A

[DaJMasta]

$5000 buys a lot of scope, you could probably manage a few hundred MHz bandwidth no problem on an R&S scope which is pretty high end for update rate and feature polish.  That budget would also get you a fair bit of lower bandwidth (350MHz or lower) scope of the current generation, Don't know if Tek/Keysight/LeCroy have great options at the pricepoint, but Rigol and Siglent have modern strong contenders and R&S's lower end scope line would fit in that price bracket with some premium fit and finish.

If you're looking for really high bandwidth, then older is the older way to go, and LeCroy probably has the highest value options for those 1GHz+ scopes.  If you don't care about bandwidth... well there are a lot of options of various levels of performance.... $5000 for a used scope with no bandwidth requirement is a really big area to draw from if you don't have specific requirements.

Maybe take a look at some of the bigger stores to see if they have something of interest?  Keysight's got an ebay store and a non-keysight brand store, I think Tek and LeCroy have some sort of official thing too, then some of the bigger test equipment dealers have a good stock to see what's available and what you may be interested in.  Maybe smaller form factor instead of boat anchor?  Maybe 10+ bits (would have to be newer, there)?  Maybe specifically a windows based (or not windows based) scope, or with some connectivity or specific option package?

[0culus]

I'm thinking 1 GHz might be a good move, as I'd like to be able to see my digital signals with good integrity (i.e. be able to display all the harmonics). I'm liking the sound of being able to fully unlock a LeCroy.

[tautech]

I'm thinking 1 GHz might be a good move, as I'd like to be able to see my digital signals with good integrity (i.e. be able to display all the harmonics). I'm liking the sound of being able to fully unlock a LeCroy.

Yeah well with a $5k budget you're at the level were a decent and new DSO is within reach like the SDS5054X that BTW also has a purchasable 1 GHz BW upgrade......and you say you wouldn't mind unlocking options. 

Info that has come to light has BW options hidden in the OS for all 5kX models from 350M -1G however no one has investigated taking the 350 all the way to 1 G AFAIK.

Wanna be first ? 

[0culus]

I don't know. Convince me that the engineering in that scope is on the level of LeCroy, R&S, or Keysight. Personally, I prefer to spend my money on the best quality stuff I can. 

[DaJMasta]

I don't know really how easy it is, I know there were reports of screwing things up and needing backups before but perhaps those issues have been sorted.  Something like the 900 series (950 or 960) is quite affordable and uses the older dedicated interface, as is the DDA-125 (I think the 120 and lower have CRTs) - a bit obtuse in terms of layout for my tastes, but powerful and responsive.  Newer scopes of theirs, the WavePro 7000/8000 series and DDA/SDA/WaveMaster equivalents are pretty powerful Windows 2000/XP based scopes that have had a fair bit of hacking and analysis done on the forum.  Beyond that, and likely still in your budget, are the more modern smaller form factor scopes.  You'll pay a fair bit more for the small form factor and newer model, but the base scope interface will be basically the same (X-Stream software on all their windows based scopes and some more modern non-windows ones), and you can still get a good amount of bandwidth for your buck.

At least for the older, larger form factor scopes, they can be a bit noisy for fans, but it's not awful and can be improved with high flow replacements.  Since they're basically just a microATX PC in a scope chassis on the windows models, it's pretty easy to upgrade to the max of the board for a bit better responsiveness/load times, and some upgrades of the mainboard to a whole new chipset (or to windows 7) have been documented in some threads around.  I've worked with a DDA-125, WavePro 960, WavePro 7200, and WavePro 7300A and have found them all to be pretty nice scopes, the first two with the older display format and OS, the remaining two with windows and X-Stream, and the only real quirk of an issue is that on the 7300A, I get a relay click and recalibration (temperature compensation, presumably) on every new acquisition not in roll mode, which is really obtuse.  In another thread it was mentioned that this was common and expected by some users, but my WP7200 never did that - just the occasional temperature compensation every few minutes like a SA alignment or similar, so I expect it can probably be figured out, I just haven't mucked around in the calibration menu to try and fix it myself, yet.

In the case of any of those, there are a good number of units for sale with software options unlocked, but hacking if effective would take care of that, though the acquisition memory options are hardware based and are not software unlockable (it seems that very large memory options may even use different ADC boards that are larger for the extra memory chips).


In any case, I'm sure there are some complaints with them, but for high bandwidth 8 bit scopes that offer a lot of bang for your buck, these used LeCroys have seemed like the best value proposition for a while now.  I'd expect a WP950 to start a bit more than $1000US, with WP7200s closer to $2000, but there are sometimes deals floating around especially if you don't mind risking buying an untested unit.

[0culus]

Is there a breakdown chart anywhere of the various LeCroy models?

[pigrew]

Although you specifically asked for scopes, it sounds like you need to also budget for a set of active probes, assuming a need to probe anything more than 150MHz. Active probes are mostly manufacturer-specific (though adapters do exist), and will easily eat up $US500 or more for a set.
 Myself, I've been using the Tek P6243 and P6205 (attached to a Tek TDS784D which has a very antiquated interface but works decently apart from few internal analysis modes).
If working with LVDS or USB, you may also need a differential probe like P6247 (even more money). I'm sure LeCroy and Agilent sold good active probes, but I don't know their model numbers off the top of my head.

[Mechatrommer]

...looking at LeCroy... I found this, for instance: eBay auction: #232562487402
Thoughts and advice are all appreciated.

for my eye?... not good enough... try below... but ymmv in case if you have other preferences to 500MHz DSO instead of cheaper GHz DSO of the same age...

$2K - 5GHz similar AFE as 6GHz version (SDA6000, i believe its upgradable) if you dont mind the BMA input (there's convertor to BNC and i'm developing myself)
DDA5005A-XXL

if somehow you hate the guy, there's another US seller @ $2.5K
DDA5005A-XL

$4K - if you insist on BNC input, then... 3GHz DSO... currently decent looking cheapest from Singapore, if you dont mind missing front frame, there's one $2K+ from Thailand...
DDA3000-XXL

the sweet 6GHz SDA6000 (before a big jump in BW and price to SDA13000 and SDA18000), currently cheapest around $4K, maybe you can offer and lucky if seller accept at half the price (like i did)
https://www.ebay.com/sch/i.html?_nkw=lecroy+6000

i'm cursed 

[nctnico]

I don't know. Convince me that the engineering in that scope is on the level of LeCroy, R&S, or Keysight. Personally, I prefer to spend my money on the best quality stuff I can. 

The hardware usually isn't the problem with scopes from China. The firmware OTOH can take long to fix. However if you have $5k to spend and 500MHz is enough I'd keep an eye on the Siglent SDS5000 series to see where the firmware development is going.
If you need 1GHz or more then the older DSOs from Agilent and Lecroy are a good option but these won't be very useful as a general purpose oscilloscope due to (generally) no peak detect mode, big size and noise.

Another option is to check for refurbished oscilloscopes. With a budget of $5k you get into a grey area where getting an old & loud boatanchor may not be the best option. Good deals can be found in Keysight's Ebay store and I'm sure other manufacturers have similar outlets. It does take some patience to wait for a good deal to appear.

[Kosmic]

If you need 1GHz or more then the older DSOs from Agilent and Lecroy are a good option but these won't be very useful as a general purpose oscilloscope due to (generally) no peak detect mode, big size and noise.

Big and noisy, yes. But, is the lack of peak detect really a problem ? My understanding was that, in peak detect mode, the oscilloscope was running as fast as possible sorting and keeping only the Min/Max samples. You can probably do something similar running at max speed and activating persistance.

To detect glitchs another option is to exploit the triggering system. Interesting post on the subject from Wuerstchenhund: https://forum.allaboutcircuits.com/blog/the-truth-about-oscilloscope-waveform-update-rates-and-why-not-to-fall-for-it.1514/

[0culus]

I don't know. Convince me that the engineering in that scope is on the level of LeCroy, R&S, or Keysight. Personally, I prefer to spend my money on the best quality stuff I can. 

The hardware usually isn't the problem with scopes from China. The firmware OTOH can take long to fix. However if you have $5k to spend and 500MHz is enough I'd keep an eye on the Siglent SDS5000 series to see where the firmware development is going.
If you need 1GHz or more then the older DSOs from Agilent and Lecroy are a good option but these won't be very useful as a general purpose oscilloscope due to (generally) no peak detect mode, big size and noise.

Another option is to check for refurbished oscilloscopes. With a budget of $5k you get into a grey area where getting an old & loud boatanchor may not be the best option. Good deals can be found in Keysight's Ebay store and I'm sure other manufacturers have similar outlets. It does take some patience to wait for a good deal to appear.

Emphasis mine. I have a Tek 7904A, so pretty much anything in the DSO realm that's new enough to not have a crt is going to be smaller I'd think. Not a huge worry for me.

[nctnico]

If you need 1GHz or more then the older DSOs from Agilent and Lecroy are a good option but these won't be very useful as a general purpose oscilloscope due to (generally) no peak detect mode, big size and noise.

Big and noisy, yes. But, is the lack of peak detect really a problem ? My understanding was that, in peak detect mode, the oscilloscope was running as fast as possible sorting and keeping only the Min/Max samples. You can probably do something similar running at max speed and activating persistance.

For general purpose use you are often looking at signals which are way below the maximum frequency and need a lower than maximum samplerate. This means that a signal will get undersampled resulting in all kinds of signals on screen which have no relation to reality. Peak-detect is very useful to see at least the (vertical) extend of the signal and give the user a hint the signal of the DUT has higher frequencies.

Edit: BTW a quiet lab is very easy to get used.

[Kosmic]

For general purpose use you are often looking at signals which are way below the maximum frequency and need a lower than maximum samplerate. This means that a signal will get undersampled resulting in all kinds of signals on screen which have no relation to reality. Peak-detect is very useful to see at least the (vertical) extend of the signal and give the user a hint the signal of the DUT has higher frequencies.

Edit: BTW a quiet lab is very easy to get used.

But then, you are limited by the memory available to your scope. With unlimited memory you could run at max speed at any time/div. So the requirement should be an healthy amount of memory or peek-detect.

For example, with my Lecroy I can sample at 4GS/s for 4ms (0.5ms/div). This is one channel and it maxout the 16Mbytes of memory available. For my usage it is definitely acceptable and I don't really need peak-detect.

[0culus]

So here's one thing I'm not clear on. For 'scopes that are really PCs with expensive peripherals, is the memory available for capturing waveform data shared with the system RAM or do some 'scopes have dedicated capture memory that's only used for waveform data?

[DaJMasta]

Acquisition memory of even moderate scope frontends outpaces the speed/latency requirements for conventional PC memory, especially when shared with other devices.  Generally, acquisition memory is its own devices controlled directly by dedicated memory controllers connected to the ADCs and trigger system.  It's this case in every one of the scopes mentioned so far, in the specific case of the windows based machines, depending on the architecture they usually connect through PCI, PCIe, or other high bandwidth interfaces (sometimes SATA), so the mainboard performs the acquisition and any hardware analysis/decoding/etc, sends that data to the PC portion, and the PC portion processes it further as needed and updates the display with it.


It's effectively the same in a scope that doesn't have a separate PC - the ADC connects to a memory controller and acquisition memory, and that system interfaces with the application processor that drives the display and handles all the screen, control input, and analysis related functions.

[Mechatrommer]

If you need 1GHz or more then the older DSOs from Agilent and Lecroy are a good option but these won't be very useful as a general purpose oscilloscope due to (generally) no peak detect mode, big size and noise.

Big and noisy, yes. But, is the lack of peak detect really a problem ? My understanding was that, in peak detect mode, the oscilloscope was running as fast as possible sorting and keeping only the Min/Max samples. You can probably do something similar running at max speed and activating persistance.

For general purpose use you are often looking at signals which are way below the maximum frequency and need a lower than maximum samplerate. This means that a signal will get undersampled resulting in all kinds of signals on screen which have no relation to reality. Peak-detect is very useful to see at least the (vertical) extend of the signal and give the user a hint the signal of the DUT has higher frequencies.

what can we ask more from 20GSps scope? (price $2-4K available used) to see glitches of more than 10GHz frequency content? any modern DSO say at 4GSps with peak detect feature can detect that kind of glitches? (priced way more than $4K new) but you have some point, high BW GHz DSO are specialized tool, we just want to get cheap here.

[nctnico]

Indeed. My point is that the older scopes with high samplerates are less suitable as general purpose oscilloscopes.

[Mechatrommer]

high BW GHz DSO are specialized tool.

just to add more to avoid misconception.... are specialized tool... that the lower BW DSOs are not capable of and certainly have no way of workaround at all. ymmv.

[David Hess]

If you need 1GHz or more then the older DSOs from Agilent and Lecroy are a good option but these won't be very useful as a general purpose oscilloscope due to (generally) no peak detect mode, big size and noise.

But, is the lack of peak detect really a problem ? My understanding was that, in peak detect mode, the oscilloscope was running as fast as possible sorting and keeping only the Min/Max samples. You can probably do something similar running at max speed and activating persistance.

Peak detection works on single shot acquisitions.

Peak detection done using persistence is envelope detection across multiple acquisitions (1) or DPO (digital phosphor oscilloscope) type operation on one or more acquisitions which would be my personal preference.  Peak detection might be considered a very limited DPO mode of operation that uses the shallowest histogram possible.

This brings up a question about the right kind of DSO to suggest.  Maybe you want a DPO type of DSO which is good at finding glitches?

(1) DSOs which support peak detection combine it with envelope detection mode to make envelope detection more effective.  But despite what Rigol says, they are distinct things.

[Ice-Tea]

If you're interested in an older LeCroy, it won't kill you to look at my signature (follow the eBay link).

Currently there's a 9354 500MHz and a DDA-120 there (almost identical to the LC585 4Ch 1GHz Scope). There's actually also a WP950 that I'm currently repairing a display issue on (also 1G) but unfortunately that one doesn't have a bezel anymore

[Mr Nutts]

If you need 1GHz or more then the older DSOs from Agilent and Lecroy are a good option but these won't be very useful as a general purpose oscilloscope due to (generally) no peak detect mode, big size and noise.

H
Peak detect? LOL! 
 
Peak detect was useful on the TDS3000 I once had to use because its memory was so small that it quickly ran out of steam (i.e. sample rate)
 
Outside of underpowered Tek scopes I never touched it again
 
My Agilent Infinum 8064 has peak detect but with 128M of memory why would I use this crutch when even at very long timebases the sample rate remains high enough?
 
I just got a Wavepro 960 which is a 2 GHz scope, and it comes with 64M memory. No peak detect but 64M memory which is enough to sustain a sufficient real-time sample rate at very long timebases

It’s big but not very noisy

And the size comes with a large display

My Waveruner LT is very compact and not loud either

Indeed. My point is that the older scopes with high samplerates are less suitable as general purpose oscilloscopes.

All of the scopes I mentioned are way better general purpose scopes than the TDS3000 has ever been
 
I wonder what you are doing to require peak detect on a modern scope with sufficient memory and which can’t be done with real-time sampling and triggers if required? Or maybe you just use it because it’s what you are accustomed to? 

And I don’t think 1 GHz is still considered “high bandwidth” when scopes now go to 110 GHz

[EEVblog]

$5000 buys a lot of scope

It does indeed.
I'd be looking outside of ebay at one of the auctions like Equipnet who advertise on the main site.
If patient you should be able to get a really high end scope, as $5k is outside the budget of the hobbyists looking for a bargain.