Least expensive but reliable used-market scope with at least 1 GHz? - Page 1
Forum section: electronics / testgear

author: Electro Fan
author_rank: Super Contributor
timestamp: October 27, 2015, 07:47:19 pm
content: Just looking for opinions but this will probably bring out some debates....So, get on your boxing glovesor better yet just be friendlyWhat is your preferred least expensive but reliable used-market scope that has at least 1 GHz of bandwidth?That's it - no other modifiers but you can make your case based on any value-added considerations such as 4 channels vs. 2, color vs. monochrome, LCD vs CRT, less bench space vs. more, good measurement features, or any other features, functions, specifications, real world experience, etc., etc.

author: nctnico
author_rank: Super Contributor
timestamp: October 27, 2015, 07:49:16 pm
content: I think Tektronix TDS744A uphacked to 1GHz / 4Gs/s.

author: dr.diesel
author_rank: Super Contributor
timestamp: October 27, 2015, 07:50:31 pm
content: Any particular project driving/requiring this?

author: Electro Fan
author_rank: Super Contributor
timestamp: October 27, 2015, 07:59:26 pm
content: Quote from: dr.diesel on October 27, 2015, 07:50:31 pmFair question - what started it was a desire to get to better rise time measurements but I'd rather not constrain a wider discussion of what folks think might be a really good 1 GHz scope in general (while keeping the price down).

author: AndyC_772
author_rank: Super Contributor
timestamp: October 27, 2015, 08:13:56 pm
content: I agree that the Tek TDS7xx series are excellent scopes, and an obvious option if you need 1 GHz on a modest budget.I had a TDS754D for a while, but it was quite noisy, kept the room warm (400W power consumption), and there was always the threat that its critical battery would finally give out and lose all the cal data. No doubt this can be worked around if you have the time and inclination, but I need my scope to earn a living, so I chickened out and swapped it for a newer Agilent.

author: Lukas
author_rank: Frequent Contributor
timestamp: October 27, 2015, 09:23:16 pm
content: Does a sampling scope suit your needs? If yes, have a look for Tektronix 7000 series mainframes with sampling plugins. Generally speaking, high bandwidth sampling scopes are much cheaper than a realtime scope with the same BW.

author: Howardlong
author_rank: Super Contributor
timestamp: October 27, 2015, 09:54:15 pm
content: Recently I managed to buy an HP 54120B mainframe, 54121A test set and cable for a total of $700 + shipping over three separate auctions over the period of about four months. The aim was to be able to look at digital signals over 100MHz and be able to see reasonably what they really look like rather than some hazy representation, Together that's a 20GHz sampling scope. The 54121A has its own TDR pulse generator built in with <=45ps rise time. The 54121A is speced for 17.5ps rise time, if you can generate such a signal. I also bought a 54006A 6GHz passive probe for $200.With the built in TDR pulse generator I achieve a 33ps system rise time on my unit. It's been pretty educational looking at this stuff in the time domain, usually I use an 8753A VNA for matching stuff, and will continue to do so, but seeing the impedance bumps in the time domain give you a different perspective.One thing to note is that the trigger is separated from the channel inputs. This means that you need to construct various contraptions out of power splitters and cables. If you really have to see what caused the the trigger (ie, you have a not very repetitive signal) you will need a delay line, and keep in mind that a delay line of sufficient length is going to affect the signal integrity. All this adds to the cost. I finally invested in an SMA torque wrench too.The 54120B is a big beast, longer than all my other boat anchors, about 25" depth, but not quite as heavy as I expected. It was the 54121A that was the expensive bit. I managed to get mine with the 3.5mm bulkhead savers and shorts attached. These are thread compatible with SMA, but take care on how you mate them, the 3.5mm receptacles don't have the teflon supports on the inner that SMAs do.Someone's trying to sell the same setup as mine for £25k on ebay at the moment, I don't think so!

author: TerraHertz
author_rank: Super Contributor
timestamp: October 28, 2015, 01:36:38 am
content: Quote from: Howardlong on October 27, 2015, 09:54:15 pmI like these too. I have a couple working, one for US$610 in 2004, another free. Plus another mainframe for spares (power supply problem) for US$75 recently.Better mention to Electro Fan that these things are 50 ohm input, and absolute maximum allowed voltage range +/- 2V. Maximum, as in more will blow the inputs. This means you have to be extremely careful with static, ensure cable conductors are shorted to ground before connecting to the scope, etc.The commonly available 'service' manual has no schematics, but Artek manuals does have the schematics for the mainframe available on CD. They are good quality but don't include the sampling head. I still don't have schematics for that.A really cool accessory is the HP N1020A TDR probe - PCB probing for 54121T. It's very nice to be able to see PCB trace impedance variations along a track. These come up now and then on ebay. eg 181505699415

author: Electro Fan
author_rank: Super Contributor
timestamp: October 28, 2015, 06:41:57 am
content: ThanksSo far it looks like a TDS700 series or a 7000 Series sampling system such as a 7S11 and S-6?The sampling system has limited voltage range?Or try duplicate Howardlong's good find with the HP 54120B, etc.Any other suggestions/considerations?

author: AndyC_772
author_rank: Super Contributor
timestamp: October 28, 2015, 07:09:06 am
content: www.fastsampling.com

author: Howardlong
author_rank: Super Contributor
timestamp: October 28, 2015, 08:44:09 am
content: Quote from: Electro Fan on October 28, 2015, 06:41:57 amYou use inline 50 ohm pads to attenuate appropriately, or you can use a 54122A instead of a 54121A which has built in variable attenuators but has a reduced bandwidth of 12.4GHz, probably not much of a problem if you're probing with a 6GHz probe though.Edit: I come with an RF background so have a reasonably large selection of SMA pads and other related paraphernalia already.

author: EV
author_rank: Frequent Contributor
timestamp: October 28, 2015, 09:10:34 am
content: Quote from: Electro Fan on October 28, 2015, 06:41:57 amYou need plugins 7T11 and 7S11 with S-2 or S-4. It is easyer to use if the pulse is pretriggered about 70 ns using external trigger.

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: October 28, 2015, 09:51:17 am
content: Quote from: Electro Fan on October 27, 2015, 07:47:19 pmIt depends on what you want to do, really. 1GHz bandwidth is pretty meaningless if the other specs aren't adequate for the task at hand.If usability was at least somewhat important then I'd say a LeCroy 9370/9374 or 9384, simply because while they are old and ugly, they offer very decent specs (1GSa/s to 4GSa/s real-time sample rates, 50k to 8M sample memory per channel), and for a few bucks can have all their advanced options enabled.On the other side quite often the successors LeCroy LC574 (4GSa/s) or LC584 (8GSa/s) can be found for the same price as a 9300 Series scope. The LC offers faster processing and color screen, and like with the 9300 Series these scopes can have all their software options unlocked for a few bucks, too.Both are pretty reliable scopes for which Service Manuals including schematics are available, and especially with the advanced options enabled they can still do lots of things that even today can only be found in high end scopes. In this age and (2nd hand) price class there's unlikely to be anything more powerful. Although their age does start to show (i.e. screen burn), and it can take some time to get a good deal amongst all the ebay sellers asking insane prices for their "untested" (yeah, right) gear. But that's a general problem.However, if money and price was of upmost importance, and usability played no role, then one can save a few bucks by getting one of the antique sampling scopes from the late 80's. They are huge, slow, loud, suck lots of power, and are only really useful for a very limited set of tasks, and due to their age and sensitive components may require a lot of babying, but these days at least they're often dirt cheap.

author: EEVblog
author_rank: Unknown
timestamp: October 28, 2015, 11:11:49 am
content: Which country?$765 buy it nowhttp://www.ebay.com/itm/Tektronix-TDS-684A-1GHz-5GS-s-4-Channel-Color-Digital-Oscilloscope-13-1F-2F-/371470646243

author: bingo600
author_rank: Super Contributor
timestamp: October 28, 2015, 04:52:03 pm
content: Quote from: EEVblog on October 28, 2015, 11:11:49 amWhoaaa - The UPS shipping offered costs $550 for DK.Thats 72% of the scope price, and both prices would be used, when adding the 25% DK import VAT here/Bingo

author: Fungus
author_rank: Super Contributor
timestamp: October 28, 2015, 05:06:30 pm
content: Quote from: bingo600 on October 28, 2015, 04:52:03 pmYes, I saw that.It's $26 if you're in the USA, $550 if you're not. I think a pegasus will fly it to your house or something.

author: nctnico
author_rank: Super Contributor
timestamp: October 28, 2015, 05:23:22 pm
content: Quote from: EEVblog on October 28, 2015, 11:11:49 amI would not get that one because it has no peak detect (AFAIK the entire Tektronix TDS600A series has no peak detect) and it has a very short memory. Without peak detect a DSO is very limited in it's use. A TDS500 or TDS700 series is a much better buy!If shipping is expensive, ask if they can ship using USPS.

author: woodchips
author_rank: Frequent Contributor
timestamp: October 28, 2015, 05:44:22 pm
content: Be warned that many > 500MHz scopes struggle to trigger. In particular the HP 54120 gives up at 1GHz even though the amplifiers will work to 18GHz.The old HP180 series scopes have sampling,as do the Tek 540 and 560 sopes.Undoubtably the best is the Tek 7000 scopes, trigger to 14GHz, wonderful.The other sampling wrinkle that is very useful is that because they don't have amplifiers, then the frequency response doesn't roll of at 12dB or so. I have had usable traces from the S2 sampler at more than 10GHz.

author: Howardlong
author_rank: Super Contributor
timestamp: October 28, 2015, 05:59:40 pm
content: Quote from: Wuerstchenhund on October 28, 2015, 09:51:17 amTotally agreed, you definitely wouldn't want to use one of the sampling scopes as your day to day scope for general development and debugging. But if you want to look at rise times, eye patterns and signal integrity for sub-nanosecond stuff such as USB 3.0 without the measuring instrument itself affecting your measurements too much then they have their place. But no, I certainly don't switch it on every day, far from it in fact. I do admit to a strange fascination of seeing changes at 10ps/div.To extend the triggering of the 54121A to 18GHz, you can use a 54118A. The basic 54121A triggers to 2.5GHz, but you'll need a 200mV p-p signal to do that (keep in mind the various attenuations from power splitters and probes). Minimum pulse width for the 54121A trigger is 200ps @ >200mV.

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: October 28, 2015, 06:32:12 pm
content: Quote from: Howardlong on October 28, 2015, 05:59:40 pmIf it has to be as cheap as possible or the bandwidth needs to be very high, I agree that they have their place. But even for eye patterns I'd rather use a real-time scope, either in real-time mode (real-time eye) or in ETS/RIS mode (where they still offer better performance than most sample scopes).QuoteWell, that's the other part (the fun of fiddling with old instruments), which isn't necessarily guided by necessity, and where normal use-case based criteria don't apply.The 54120 is certainly an interesting scope, although a very specialized one. I wish I had the space for one.

author: edavid
author_rank: Super Contributor
timestamp: October 28, 2015, 07:38:52 pm
content: Quote from: Electro Fan on October 28, 2015, 06:41:57 amIf you want reliability, I don't think you want a 7000 series sampling setupYou could also consider a Tek 11801, which is similar to the HP 54121, but uses plugin sampler heads instead of the separate box.

author: robert_
author_rank: Regular Contributor
timestamp: October 28, 2015, 07:52:53 pm
content: Id go for Lecroy 93xx over a TDSxxx any day.Nice large CRT display, long memory (nothing <50k/channel, and up to 8M on some) and seem to be much more reilable, no leaking SMT capacitors. Also you get full service manuals incl. schematics, which Tek doesnt.Also, 1Ghz: Tek 7104. Huge, loud, power hungry, but its a 1Ghz realtime analog scope. Not that it would be too useful, but it exists.

author: Electro Fan
author_rank: Super Contributor
timestamp: October 28, 2015, 10:08:39 pm
content: Quote from: EV on October 28, 2015, 09:10:34 amI think the 7000 is the preferred route.... It seems that the 7T11 and 7S11 are not both needed, seems like 7S11 should do it, yes? Then comes the question of what are the tradeoffs between S-6 and say S-4, 3, 2, etc? And finally, which probe?Any info/suggestions along these lines would be very welcome. Thx

author: dom0
author_rank: Super Contributor
timestamp: October 28, 2015, 10:43:51 pm
content: You absolutelyrequireboth a 7T11 and a 7S11 for a sampling scope.

author: Electro Fan
author_rank: Super Contributor
timestamp: October 29, 2015, 01:05:37 am
content: Quote from: dom0 on October 28, 2015, 10:43:51 pmWow, I definitely missed on this. Thanks for the heads-up.

author: EV
author_rank: Frequent Contributor
timestamp: October 29, 2015, 07:44:45 am
content: Quote from: Electro Fan on October 28, 2015, 10:08:39 pmYou need both plugins.S-2 has 50 Ohm GR874 connector and needs no probe. Risetime is 50 ps.S-3 has probe connected to it. Rise time is 350..500 ps dependind on the used attenuator.S-4 has 50 Ohm SMA connector and need no probe. Rise time is 25 ps.S-6 is for 7S12 TDR. I have not used it with 7S11.

author: Howardlong
author_rank: Super Contributor
timestamp: October 29, 2015, 01:36:19 pm
content: As a matter of interest, what is the technology behind these old sampling scopes?I assume there's a sample and hold, but what technologies were used to achieve such a tiny sample time?Regarding the timing relative to trigger, how did that work? I realise you can do random or sequential, but at some stage there needs to be very low jitter picosecond accuracy timing involved, how did they achieve that?

author: Berni
author_rank: Super Contributor
timestamp: October 29, 2015, 01:46:27 pm
content: One important question to ask if is you are looking to get a proper real time scope or is a sampling scope fine?

author: nctnico
author_rank: Super Contributor
timestamp: October 29, 2015, 02:00:01 pm
content: Quote from: Howardlong on October 29, 2015, 01:36:19 pmUsually a diode sampler. That is the easy part. Triggering and time correlation are a different story.

author: Electro Fan
author_rank: Super Contributor
timestamp: October 29, 2015, 08:08:02 pm
content: Quote from: EV on October 29, 2015, 07:44:45 amThanks - some questions:If the S-2 has a risetime of 50 ps (plenty fast in my book), what is the downside to a S-2?- if the benefit of a S-4 is 25ps I can forgo that; if the benefit of the s-4 is the SMA connector I can get around that on the S-2 with a GR874 to BNC adapter... I think; not to say the S-2 wouldn't be preferred if one can be found...When you say no probe is needed where is the signal coming from? (I need an overview of the 7000 sampling system architecture).The original goal was to be able to measure risetime on a 1GHZ or faster signal...Thanks

author: Electro Fan
author_rank: Super Contributor
timestamp: October 29, 2015, 08:11:10 pm
content: Quote from: Berni on October 29, 2015, 01:46:27 pmGood question. As mentioned, the original goal was to measure risetime on 1 GHz or faster signals. What are the differences between a proper real time scope and a sampling scope?Your question caused me to go look for/find this:http://electronicdesign.com/test-amp-measurement/what-s-difference-between-real-time-and-sampling-oscilloscopes-seems like for higher bandwidth at lower cost for repetitive signals that are not difficult to trigger the sampling approach will be better, including less jitter?- seems like for more challenging trigger requirements and deeper analysis (but maybe for relatively slower signals and with higher cost) the real time scope would be better?FWIW, I have noticed on my 2467B that under some circumstances a pulse generator signal with a risetime of perhaps 700ps or less will drift; it seems to happen more with certain cables or cable lengths. I'm not sure if this drift is considered jitter, or if it's something else; perhaps the drift would be less with a better/faster real-time scope or perhaps it would be less (more stable) with a sampling scope?- feel free to add further clarificationsThx

author: Electro Fan
author_rank: Super Contributor
timestamp: October 29, 2015, 08:44:19 pm
content: A couple of these comments from Howardlong reflect some of my thinking:Quote from: HowardlongQuote from: HowardlongThe current objective is to be able to attain better risetime measurements (ie, to be able to measure risetime for 1 GHZ signals, or faster if affordable) but anything that gives better measurement of signal performance in general along with other improved visibility into waveform and signal attributes would be a positive. The challenge is to do it at a good cost since it's strictly an educational hobby with no chance of revenue generation.So far, the idea of adding some plug-ins to a Tek 7000 seems like the path of least resistance....The one thing I most miss on the 7000 is cursors (go figure) along with the general lack of digital readout measurements but if I can get from the performance of a 500MHz 7904/7A29 to some of the performance and "observable measurements" normally associated with a 1 GHz or faster scope then the sampling plug-in approach seems like a reasonable path.I'm definitely up for leaning more about the sampling configs of the 7000.

author: EV
author_rank: Frequent Contributor
timestamp: October 29, 2015, 09:54:08 pm
content: Quote from: Electro Fan on October 29, 2015, 08:08:02 pmAs I told they have 50 Ohm input connector. You can connect the signal to it with RG58 cable. If the voltage is too big (max value is 5 V) you need also attenuators.You can find free manuals for 7T11, 7S11, S-2 and S-4 by google. You can get more info from them.

author: rx8pilot
author_rank: Super Contributor
timestamp: October 29, 2015, 10:03:48 pm
content: I have a TDS754C and really like it overall. It's old, big, and does not have some of the bells and whistles the newer models have. It does, however, work every day with no issues discovered yet. if the CRT every dies, it has VGA to extend its life a little if I need. I am using it as a step to a new and modern $15k+ scope when I have the cash to pay for it.

author: Electro Fan
author_rank: Super Contributor
timestamp: October 29, 2015, 10:07:30 pm
content: Quote from: EV on October 29, 2015, 09:54:08 pmOk, I understand that the 50 Ohm connector (or GR874) can be used via a coax cable rather than a probe (I thought when you mentioned that no probe was needed that maybe the signal was routed internally from another plug-in) - now I understand. ThxIf a probe were to used is there any particular Tektronix probe (from the 7000 era or more recent) that is recommended for use with a S-4?

author: Electro Fan
author_rank: Super Contributor
timestamp: October 29, 2015, 10:13:52 pm
content: Quote from: rx8pilot on October 29, 2015, 10:03:48 pmThese look like fine scopes but just to confirm the TDS754C is 500MHz? Need to go to 784 for 1 GHz? Thx

author: rx8pilot
author_rank: Super Contributor
timestamp: October 29, 2015, 10:21:03 pm
content: Quote from: Electro Fan on October 29, 2015, 10:13:52 pmThat is correct - but it is the same box minus some filter caps and software keys.

author: nctnico
author_rank: Super Contributor
timestamp: October 29, 2015, 10:21:36 pm
content: I think you can uphack the TDS754 to a TDS784. This info is somewhere on the forum but you'll need to calibrate the scope afterwards for frequencies >500MHz.

author: rx8pilot
author_rank: Super Contributor
timestamp: October 29, 2015, 11:02:08 pm
content: Quote from: nctnico on October 29, 2015, 10:21:36 pmYep, I have seen it done. I am too chicken to mess with it. One small mistake will send me scrambling to fix a 15 year old scope. I may try it when I order my new scope - just for fun.

author: Electro Fan
author_rank: Super Contributor
timestamp: October 29, 2015, 11:06:25 pm
content: On the Tek 7000 series...The Tek S-2 spec says:Operating Input Voltage Range: +1V to -1V P-P signals. Step signals greater than 200mV may require more than 1 dot to display 100% of the step transitionMaximum Input Voltage: +/-5VDC or sine wave of 10V P-P up to 10MHzDoes that mean for anything above 10MHz the limit is +1V to -1V P-P ?Likewise on the S-4 the spec says Signal Voltage Maximum Operating is 1VPP, but on the front of the unit it says +/- 5V Max.http://bee.mif.pg.gda.pl/ciasteczkowypotwor/Tek/S4_In.pdfUnder what conditions is it safe to go to +/- 5V? Thx

author: OldSchoolTechCorner
author_rank: Frequent Contributor
timestamp: October 29, 2015, 11:15:53 pm
content: The TDS784 is a good one. Only issues is uses tantalum capacitors and they are prone to fail and burn hole though board. A tantalum capacitor is actually much like a bomb or thermite. It has an oxidizer (manganese dioxide) and fuel (tantalum). You'll only need to ignite it. Well the electricity is also there so just start the countdown clock. The reason why I replace them as they age. The older series Tektronix DSO's you have to replace every SMD electrolytic and though hole and neutralize and clean the boards.

author: Electro Fan
author_rank: Super Contributor
timestamp: October 29, 2015, 11:32:55 pm
content: a little bit off topic but saw this discussion/comparison of sampling scopes:https://books.google.com/books?id=JP3sCAAAQBAJ&pg=PA64&lpg=PA64&dq=tekronix+s-4+vs+s-6&source=bl&ots=YVKKgsCnqU&sig=R0GUfGIQ6S92AR8dzeUOTF7AjCM&hl=en&sa=X&ved=0CD4Q6AEwBWoVChMIp-bu9-royAIVEN1jCh0wZgAQ#v=onepage&q=tekronix%20s-4%20vs%20s-6&f=false

author: edavid
author_rank: Super Contributor
timestamp: October 30, 2015, 01:09:22 am
content: Quote from: Electro Fan on October 29, 2015, 08:08:02 pmI believe the S-2 actually has a 75ps risetime (4.6GHz bandwidth). Downside is the GR connector... GR adapters tend to add aberrations.

author: Electro Fan
author_rank: Super Contributor
timestamp: October 30, 2015, 04:07:11 am
content: Quote from: edavid on October 30, 2015, 01:09:22 amYes, I think 75ps is the spec.How big a deal is the GR aberration? On 10 typical measurements, how many are likely to be impacted by an aberration? Kind of a subjective/random question I realize - just trying to get some impression of the impact. Thx

author: Rupunzell
author_rank: Frequent Contributor
timestamp: October 30, 2015, 06:22:21 am
content: Start here at the Picosecond Pulse Labs app notes to get an idea of what is involved.http://picosecond.surtos.com/techinfo/content.asp?spid=19Bernice

author: TSL
author_rank: Regular Contributor
timestamp: October 30, 2015, 06:49:55 am
content: A HP 54720A or D is a reasonable scope. Plugin modules to 2Ghz, color screen etc. i have one with 54712A and 54721A modules and that's fine for me. $1000Us will buy you a fine specimen thus...http://www.ebay.com/itm/HP-HEWLETT-PACKARD-MODEL-54720A-OSCILLOSCOPE-W-TWO-54721A-AMPLIFIERS-1159-/401018882278Yes its big and a little noisy but its exceptionally capablerf-loop had high praise for them too...https://www.eevblog.com/forum/chat/is-a-hp-agilent-54721a-a-decent-oscilloscope/More info on it here...http://www.keysight.com/main/facet.jspx?&cc=AU&lc=eng&k=54720A&sm=g

author: Electro Fan
author_rank: Super Contributor
timestamp: October 30, 2015, 06:57:47 am
content: Quote from: Rupunzell on October 30, 2015, 06:22:21 amThanks for the link to the info. Picosecond Pulse Labs looks like an intense / focused outfit; looks like they are now part of Tektronix?http://www.tek.com/document/news-release/tektronix-acquires-picosecond-pulse-labsPrivately-held Picosecond Pulse Labs, based in Boulder, Colorado, offers products that include ultra-high-speed pattern generators,the world's fastest pulse generators and highest bandwidth sampler modules. The company recently introduced the PatternPro line that includes multi-channel 32 Gb/s data generators and analyzers for 100G/400G applications.

author: Electro Fan
author_rank: Super Contributor
timestamp: October 30, 2015, 07:25:44 am
content: Quote from: TSL on October 30, 2015, 06:49:55 amI'm sure it's high performance but it looks a bit esoteric. I briefly had a HP scope - it had some good attributes but I think I'm with whoever said "Tektronix for oscilloscopes, HP for everything else" - I'm kind of a Tek scope fan. And a closet Keysight fan. Not to say I wouldn't take a LeCroy or HP or another scope - almost any oscilloscope looks good to me.Having said that I always admire your posts and I know rf-loop also has a lot knowledge and experience - and he definitely knows what he likes:Quote from: rf-loop on February 22, 2011, 07:52:53 pmand he also knows what he doesn't like..... a "cross word puzzles" UIQuote from: rf-loop on February 22, 2011, 07:52:53 pm- that comment by rf-loop was very FUNNY!

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: October 30, 2015, 12:08:57 pm
content: Quote from: TSL on October 30, 2015, 06:49:55 amThat's only true for its bandwidth and modularity (which includes optical inputs). As a scope per se, the 54720 is actually pretty basic. Trigger, math and measurement capabilities are somewhat limited for a scope in this class (it does have statistics, though), and processing is painfully slow. FFT on this thing is a real dog even though it only uses a few thousand points.We had 54720As and Ds when they were current (~1995?), and they were great for the things we needed them to do (TDR, jitter measurements), but as general purpose scopes they weren't great even at those days, especially when considering the input limitations of the various modules. Many people also didn't like the typical HP single knob user interface (also found on the older 545xx Series scopes), although I have to say I did really liked it.Don't get me wrong, the 54720 can be exceptionally great value for money if you need very high bandwidth, the available optical inputs and the modularity, but outside some niche areas it's not much better than any other digital scope from the early '90s. The same money ($1000 for an untested 54720D) can get you much more versatile scopes that satisfy the 1GHz bandwidth requirement and make better general purpose scopes.Quote from: Electro Fan on October 30, 2015, 07:25:44 amThe thing with that old saying"Tektronix for oscilloscopes, HP for everything else"is that it was true when analog scopes were still current, and Tek was without doubt a leader in analog scopes who has pushed technology forward. However, that isn't equally true in regard to digital scopes, in fact Tek has been pretty much a follower when it comes to DSOs, and pushing DSO technology was left to mostly LeCroy and (to some extend) Agilent/Keysight. Plus many of the old Tek's suffered from a capacitor plague, and the UI was pretty horrendous even by those days' standards.If you want an old digital scope I'd pretty much focus on LeCroy and HP/Agilent.I don't know if the reason you started this thread is for curiosity or if you're thinking on buying a scope, but if its the latter then you should first get your requirements right (i.e. what you want to do with the scope, why you think you need 1GHz bandwidth etc), then sort out your budget, then find out what it buys you and then do some thorough research (i.e. read the manuals for each scope to get an impression on how they work and what they can do, talk to users that do use one of the scopes for similar things you want to do, find out what the weak points are etc), and then decide based on your findings.

author: Electro Fan
author_rank: Super Contributor
timestamp: October 30, 2015, 09:42:47 pm
content: Quote from: Wuerstchenhund on October 30, 2015, 12:08:57 pmI 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. The only reason for mentioning the Tek/HP saying was that my experience with the HP analog scope seemed to confirm the saying. In the digital era it's a different situation, I get it.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 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). 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.I appreciate all the advice here - some of the recommended scopes would add more functionality but this thread helped me realize that I'm sitting on just a few incremental pieces short of what I need for pretty fast risetime viewing with the Tek 7000.

author: Howardlong
author_rank: Super Contributor
timestamp: October 30, 2015, 10:46:47 pm
content: It sounds like you have a similar intrigue that I do into insanely tiny time.When I first built computers in the 70s, 450ns was the typically static RAM access time, and at the time we were amazed at that.Although I do plenty in RF mostly in S band and below (although I have been known to go up to K band experimentally), pretty much everything is measured in the frequency domain.Much more recently, I have become more interested in looking at stuff like transmission lines in the time domain as well (as well as the frequency domain with VNAs as I traditionally have done), and it gives an interesting, and different, perspective.What I would say is that if you did go to a 1GHz bandwidth scope from a 500MHz one and are trying to measure ~300ps rise times such as with the JW pulse generator, there is a difference, but it's nowhere near as much as you'll get with a sampling scope in the 10s of GHz. What I would recommend, if you go for a real time scope in the low GHz is to get one that works in equivalent time too. Neither interpolation nor fixed, limited period sampling give a faithful reproduction of what's happening, there will inevitably be some bastardisation, but with ETS you can avoid the interpolation and sampling period limitations, and will generally get a fair bit closer on repetitive signals.Even with ETS, typically the next problem to deal with is front end analogue artefacts like overshoot and/or ringing that often might only exist inside the scope! One way to show what's happening is to shoot a step from a TDR such as that in a sampling scope set up and look at the response when it hits a 1GHz scope's BNC, it's rarely pretty.A high speed sampling scope is not the same as a regular day to day scope, almost like a spectrum analyser isn't like a regular scope or a kettle isn't an oven, they are different tools for different jobs. My guess is that if, like me, you invest in a 1GHz scope after using 500MHz units, it's just won't be enough.... you have been warned!

author: KE5FX
author_rank: Super Contributor
timestamp: October 30, 2015, 11:03:31 pm
content: Quote from: Electro Fan on October 30, 2015, 09:42:47 pmDon't know if anyone has suggested the Tektronix TDS 694C. It's a good way to get all the way to 3 GHz without resorting to sampling. They can sometimes be had for around $1K, and it's a good idea to buy another one as a parts mule if possible.They aren'tgreat3 GHz scopes since they "only" sample at 10 Gs/s, but they get the job done, and they are extremely good at 1 GHz. They are new enough that they don't suffer from the infamous Tek capacitor plague.Trigger chip failures are very common, but strangely enough, as I recently learned, the 694C has a couple of spares on the board that are soldered in but unused. So you can save some bucks by buying one with a triggering problem and swapping the chips.True to Tektronix's usual balls-to-the-wall engineering practice, you need to use a fan on the acquisition board when servicing it with the power on. A lot of people didn't know/care about that, and my personal suspicion is that this is what causes a lot of the triggering failures.Point being, these scopes are somewhat cheaper than they really ought to be, considering how good they are.Edit: they do require 50-ohm probes, which is something else you have to budget for. This is true of any scope once you go above 500 MHz, where high-impedance passive probes become useless. Tek's active probes, like the P6245, are ideal.

author: Electro Fan
author_rank: Super Contributor
timestamp: October 31, 2015, 12:42:36 am
content: Quote from: Howardlong on October 30, 2015, 10:46:47 pmHoward, if you or others here would be up for an educational post on the fundamentals of ETS vs. the alternative(s) and anything significantly related - either here or in a fresh thread - that would be good. I think there is an entire layer of distinctions I'm not really seeing much less understanding. Thanks, EF

author: Electro Fan
author_rank: Super Contributor
timestamp: October 31, 2015, 12:51:43 am
content: Quote from: KE5FX on October 30, 2015, 11:03:31 pmI'm sure I'm comparing apples to watermelons, but what is the significance of the Tek S-4 spec that says it has a bandwidth of 14.5 GHz? I realize the sampling head is just part of the Tek 7000 architecture but what will that 14.5 GHz do or not do vs. the 3 GHz and 10Gs/s of the TDS694C? Thanks

author: Electro Fan
author_rank: Super Contributor
timestamp: October 31, 2015, 12:58:26 am
content: The plot thickens. I noticed that the standard Tek configuration refers to the use of a pulse generator with a trigger out. In my case I just have my two fairly simple JW pulse gens - neither of which has a trigger out.I'm trying to digest the Tek manual (it seems to offer some alternative setups) but if anyone has any suggestions on the easiest way to connect and measure a JW pulser (without a trigger out) to the Tek 7000/Tek 7S11 with Tek S-X/Tek 7T11A please let me know. Thankshttp://exodus.poly.edu/~kurt/manuals/uploads/TEK%207T11A.pdf- see discussion on 2-6 under "Observing a Fast-Rise Pulse"

author: KE5FX
author_rank: Super Contributor
timestamp: October 31, 2015, 01:29:42 am
content: Quote from: Electro Fan on October 31, 2015, 12:51:43 amIf you know you're always going to be viewing repetitive signals that will look the same at every trigger, then a sampling scope can be a good way to go. But they are finicky to set up and use, and there are some things they either can't do at all or aren't very good at. There's a deckherethat covers the major differences. The 7000-series samplers areveryfinicky to use, lacking any built-in intelligence for setup and triggering.The 694C is a real-time scope that can capture up to 100K points (IIRC) at 10 GS/s in one single-shot acquisition. So while you could use a sampling scope to look at an eye diagram, for instance, you could use a 694C to look at specific glitches in a data stream. It's an ordinary scope just like any other, except that its 3 dB bandwidth is 3 GHz. Kind of a jittery display, but it's a wonder they could do it at all in the early 1990s.

author: Electro Fan
author_rank: Super Contributor
timestamp: November 01, 2015, 03:24:46 am
content: Quote from: KE5FX on October 31, 2015, 01:29:42 amThat was a very good deck - very informative - I hadn't previously been able to understand how the relatively slower sampling rate could sample the faster signal. Both approaches seem to have good merit - just depends on the functionality required and the affordable budget. Thanks for the link.

author: Electro Fan
author_rank: Super Contributor
timestamp: November 01, 2015, 03:26:56 am
content: Just re-posting in case anyone has any thoughts on how to deal with triggering for this.... ThxQuote from: Electro Fan on October 31, 2015, 12:58:26 am

author: edavid
author_rank: Super Contributor
timestamp: November 01, 2015, 03:43:54 am
content: Quote from: Electro Fan on November 01, 2015, 03:26:56 amYou misread that, you don't need a pretrigger to measure a pulse generator's risetime.(In some situations, it's handy to have a DL11 or 7M11 though.)

author: Electro Fan
author_rank: Super Contributor
timestamp: November 01, 2015, 04:34:54 am
content: Quote from: edavid on November 01, 2015, 03:43:54 amThanks, so the diagram is just showing an optional triggering capability? I guess the 7T11 and 7S11 talk to each other via some channel on their adjacent location in the mainframe and triggering happens manually with 7T11 trig level knob? Thx

author: EV
author_rank: Frequent Contributor
timestamp: November 01, 2015, 07:32:12 am
content: Quote from: Electro Fan on November 01, 2015, 04:34:54 am7T11 and 7S11 must be sibe by side. They have connectors there and are connected to each other.As I told earlier it is easyer to use if you have 70 ns pretriggered pulse connected to ext-trigger. I think in your picture is Tek 284 pulse generator. It has this kind pretriggered pulse.If you are going to see JW pulse with these plugins you are in trouble. The pulse must be attenuated at least 20 dB to be seen on the tube screen. You must use internal trigger because you dont have pretriggered pulse. The JW pulse is so narrow that there can be difficulties to get triggering work. It will not be easy to see the pulse. Anyway it is better to start practice with something like 1 MHz square wave signal with 250 mV amplitude.

author: Electro Fan
author_rank: Super Contributor
timestamp: November 01, 2015, 08:20:49 am
content: Quote from: EV on November 01, 2015, 07:32:12 amThe 284 looks like a very nice piece of equipment but it is out of my justifiable budget. So, the question is, can a fairly rapid pulse with a rise time of less than 500ps be captured by the 7S11/7T11 combo with one of the Tek S-X sampling heads? According to the specs even the S-1 (at 350ps) should be able to do it.I realize that some JW pulse gens produce a very narrow "peaky" pulse - I have one of those (shown in the first photo) and I'd like to figure out how fast it's rise time really is - which is what started me on this mission. I also have a pulse generator (on a board made by Tektronix) that has a flatter top on the pulse - it is shown in the second and third photos. It appears to produce about a 20ns wide pulse, so presumably the Tek 7000 sampling system should be able to pick this up in terms of the pulse duration. Supposedly, the Tek Pulse Gen board is capable of a rise time of <200ps - so this is what I'd like to see with the 7S11/7T11.What I am a little nervous about is exceeding the voltage capacity of the sampling system. My peaky pulse gen does seem to produce a pulse that is on the order of 7-8 volts Pk-PK (I'm not sure why or if it is operating properly). But the Tektronix pulse gen seems to produce a pulse that is well under 1 Volt Pk-Pk (less than 350mV), so I'm thinking that should work.See any reason why the pulse shown in the second and third photos won't be displayable on the Tek 7000 (S711/S-1/7T11) sampling system? The only reason I see that it might not work is if there is an issue with the triggering. If I understood edavid's post he seems to think it will trigger ok.Thanks for the help/advice.

author: Howardlong
author_rank: Super Contributor
timestamp: November 01, 2015, 08:24:17 am
content: EF: I did a video showing the 54120B/54121A sampling scope combo and its TDR step generator for use in measuring the rise times of assorted scopes, including switching between real time and ETS on scopes that supported it.

author: Berni
author_rank: Super Contributor
timestamp: November 01, 2015, 08:46:05 am
content: I built one of those Jim Williams pulse gens. The transistor i used in it seamed to not want to reverse breakdown anywhere near where the datasheet said it would so i ended up running the circuit from over 100V DC and that made 30V output pulses that i had to run trough an attenuator to get in to my scope. I got 160ps rise out of mine in the screenshot. It appears that this is about as fast as JW pulse gens go. Enugh to test the bandwidth of scopes up to 1GHz but past that not so much.The pulses are indeed very short unless you use some trick to extend them (I seen a coax cable transmission line used for that). I would guess a sampling scope would have a lot of trouble triggering off this.

author: Electro Fan
author_rank: Super Contributor
timestamp: November 01, 2015, 08:59:14 am
content: Quote from: Howardlong on November 01, 2015, 08:24:17 amHoward, that is an EXCELLENT video! The star of the show is a toss-up but I think the 54120B/54121A comes in second and you come in first!(The performance of the 54120B/54121A is really something wonderful.)Dave, if you happen to catch Howard's video it might be worth featuring. Between the various scopes/test equipment, the few tens of picosecond performance, and the education..... it's delightful!EF

author: Howardlong
author_rank: Super Contributor
timestamp: November 01, 2015, 09:13:47 am
content: EF: many thanks.I am pretty new to this, so there may be some corrections that come out. I am having second thoughts on the overshoot on the two Agilents, it may be largely due to a designed filter response rather than limitations on the analogue side or impedance bumps.

author: Electro Fan
author_rank: Super Contributor
timestamp: November 01, 2015, 09:18:48 am
content: Quote from: Berni on November 01, 2015, 08:46:05 amYes, I think the JW pulsers with the peaky pulse are challenging - both because of the short/peaky duration and also possibly due to the fairly high voltage - although it looks like you got it captured on your scope. It's my understanding that Jim Williams also designed another version of the pulse generator that had a wider pulse.For what I have in mind I'm inclined to use the pulse gen built into a Tektronix demonstration board; think the >20ns wide pulse will ease the measurement process.

author: Howardlong
author_rank: Super Contributor
timestamp: November 01, 2015, 09:26:09 am
content: Quote from: Berni on November 01, 2015, 08:46:05 amIt's not only the trigger pulse width, it's also that the gap between pulses is very long and not at all stable, so you'll probably need to see the trigger pulse itself. As well as probably needing to extend the pulse (or get a 54118A) you'd need a delay line such as HP 54008A or the Tek equivalent to allow you to see the trigger. Note that by their very nature, delay lines will affect your signal to varying degrees.

author: dom0
author_rank: Super Contributor
timestamp: November 01, 2015, 09:30:07 am
content: Am I the only one who thinks that you can't really measure a meaningful rise time with a signal that never reaches a reference level (i.e. flat top)? You'd have to measure with something that's guaranteed to be fast enough the pulse height first...

author: Electro Fan
author_rank: Super Contributor
timestamp: November 01, 2015, 09:35:11 am
content: Quote from: dom0 on November 01, 2015, 09:30:07 amI don't think you are the only one. I agree with what you are saying.Unless we are sure the measuring system is capable of performing better/faster than the DUT I don't see how we can depend on the measurement. I'm not sure that I know how wide a pulse needs to be for a scope to determine where the top is, but I believe that even if a pulse is wide enough, if the pulse's rise time is faster than the scope's rise time then what scope is going to show is largely it's own limiting rise time. I think we saw this in Howard's video.So there are two issues here: One issue is whether the scope's rise time is fast enough to reveal the DUT's rise time. The second issue, which is related to the first, is whether the pulse from the DUT is wide enough (long enough in duration) for the scope to effectively find the top of the pulse.I could be wrong about this, but that's the way I understand it so far.

author: EV
author_rank: Frequent Contributor
timestamp: November 01, 2015, 10:08:01 am
content: Here is the best I could do with my Free-Electrons JW pulser. I used 20 dB attenuator, internal triggering and random sampling. Scope is Tek R7103 with 7T11 and 7S11 (S-4) pluins.

author: Berni
author_rank: Super Contributor
timestamp: November 01, 2015, 10:11:11 am
content: I agree it should be a proper step rather than a short pulse for testing rise time, but it turns out its not all that easy to create a 10s of picosecond rise time pulse out of things you might have laying around the lab.In my case the scope had a specified rise time of 85ps so the pulse generator was the limiting factor here. Being a modern real time scope it has no trouble triggering on that.Given the difficulty of properly triggering these sampling scopes are they useful for anything else than looking at quick rise times or perhaps looking at the signal integrity of a stable clock signal?

author: EV
author_rank: Frequent Contributor
timestamp: November 01, 2015, 10:45:38 am
content: Quote from: EV on November 01, 2015, 10:08:01 amHere is my picture again and picture By Free-Electron with 33 GHz scope.

author: JoeO
author_rank: Frequent Contributor
timestamp: November 01, 2015, 10:46:24 am
content: "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?

author: Howardlong
author_rank: Super Contributor
timestamp: November 01, 2015, 10:53:13 am
content: Quote from: Berni on November 01, 2015, 10:11:11 amAs long as you have a frequent, regular, repetitive signal they are fine, but they do indeed have limitations. For checking signal integrity and eye diagrams, generally those features go hand in hand, and that's the point of a sampling scope. They're useless for single shot or infrequent or irregular signals. There are some similarities to CROs in that respect, especially in being unable to see pre-trigger (or even immediately post trigger) without a delay line. I guess as I was brought up on CROs, I can live with it! Imagine the awe I had when I had my first DSO and could see pre-trigger, it was like magic, some kind of time machine!

author: EV
author_rank: Frequent Contributor
timestamp: November 01, 2015, 11:17:24 am
content: Here is the same picture with TEK R7633 scope. Store button is on.20 dB attenuator, internal triggering and random sampling.

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: November 01, 2015, 11:29:41 am
content: Quote from: Electro Fan on October 30, 2015, 09:42:47 pmIf they arebetteris 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.QuoteI see. That changes things a bit.QuoteWell, 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)QuoteWell, 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).

author: Electro Fan
author_rank: Super Contributor
timestamp: November 01, 2015, 12:29:39 pm
content: Quote from: JoeO on November 01, 2015, 10:46:24 amI 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).

author: KE5FX
author_rank: Super Contributor
timestamp: November 01, 2015, 08:13:26 pm
content: Quote from: Wuerstchenhund on November 01, 2015, 11:29:41 amThe 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.

author: nctnico
author_rank: Super Contributor
timestamp: November 01, 2015, 09:26:21 pm
content: 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.

author: KE5FX
author_rank: Super Contributor
timestamp: November 01, 2015, 11:34:39 pm
content: Quote from: nctnico on November 01, 2015, 09:26:21 pmIt 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!

author: Howardlong
author_rank: Super Contributor
timestamp: November 02, 2015, 08:30:15 am
content: Quote from: EV on November 01, 2015, 11:17:24 amInteresting, 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? ;-)

author: EV
author_rank: Frequent Contributor
timestamp: November 02, 2015, 11:20:34 am
content: Quote from: Howardlong on November 02, 2015, 08:30:15 amI 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.

author: EV
author_rank: Frequent Contributor
timestamp: November 02, 2015, 11:52:01 am
content: Here is a new picture from R7633 with storage level adjusted bigger.

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: November 02, 2015, 05:51:04 pm
content: Quote from: KE5FX on November 01, 2015, 08:13:26 pmIt 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.QuotePretty 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.QuoteSub-$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.QuoteWell, 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.QuoteUnderstandable 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.

author: edavid
author_rank: Super Contributor
timestamp: November 02, 2015, 06:06:22 pm
content: Quote from: Wuerstchenhund on November 02, 2015, 05:51:04 pmHere's a perfectly nice one that sold for $1263:http://www.ebay.com/itm/Tektronix-TDS694C-3GHz-4-Channel-Oscilloscope-Options-1M-HD-/131589284202I've noticed that you like to overstate the price of used Tek scopes, and understate used LeCroys

author: Jwalling
author_rank: Unknown
timestamp: November 02, 2015, 06:13:33 pm
content: Quote from: KE5FX on November 01, 2015, 11:34:39 pmHi 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)

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: November 02, 2015, 06:14:06 pm
content: Quote from: edavid on November 02, 2015, 06:06:22 pmGreat. 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:mhQAAOSwQPlV9dquhttp://www.ebay.com/itm/Tektronix-TDS694C-Digital-Oscilloscope-4Ch-3Ghz-10Gs-s-Options-/311439784843?hash=item488341fb8b:g:V0EAAOSwyQtV7D5OQuoteNot 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.

author: Jwalling
author_rank: Unknown
timestamp: November 02, 2015, 06:28:48 pm
content: Quote from: Wuerstchenhund on November 02, 2015, 06:14:06 pmAnd one of the most important in auction-style listings: Just how bad someone wants it!Jay

author: edavid
author_rank: Super Contributor
timestamp: November 02, 2015, 06:40:22 pm
content: Quote from: Wuerstchenhund on November 02, 2015, 06:14:06 pmSo 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?

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: November 02, 2015, 07:05:17 pm
content: Quote from: edavid on November 02, 2015, 06:40:22 pmIt'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.Quote from: Jwalling on November 02, 2015, 06:28:48 pmExactly. 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

author: nctnico
author_rank: Super Contributor
timestamp: November 02, 2015, 08:00:38 pm
content: 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.

author: KE5FX
author_rank: Super Contributor
timestamp: November 02, 2015, 08:52:19 pm
content: Quote from: Jwalling on November 02, 2015, 06:13:33 pmNo, 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.)Quote from: Wuerstchenhund on November 02, 2015, 05:51:04 pmGood 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.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.

author: Howardlong
author_rank: Super Contributor
timestamp: November 02, 2015, 09:10:41 pm
content: FolksOne 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 @ 18GHzHP 11742A SMA inline blocking capacitorWeinschel 1515-1 18GHz SMA resistive power splitter2 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.

author: Electro Fan
author_rank: Super Contributor
timestamp: November 02, 2015, 09:49:47 pm
content: Quote from: Howardlong on November 02, 2015, 09:10:41 pmRoger thatSince 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...

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: November 03, 2015, 10:31:30 am
content: Quote from: KE5FX on November 02, 2015, 08:52:19 pmIf you can get one at $1500, yes.QuoteIt'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) memoryTimebase 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/s2.5GHz3us/div1GS/s500MHz2.5GS/s1.25GHz5us/div500MS/s250MHz2.5GS/s1.25GHz10us/div250MS/s125MHz1GS/s500MHz20us/div125MS/s62.5MHz500MS/s250MHz30us/div100MS/s50MHz250MS/s125MHzThe 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) memoryTimebase 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/s1GHz1ms/div25MS/s12.5MHz1GS/s500MHzThe 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.QuoteI 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).

author: nctnico
author_rank: Super Contributor
timestamp: November 03, 2015, 11:45:42 am
content: 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.

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: November 03, 2015, 12:01:45 pm
content: Quote from: nctnico on November 03, 2015, 11:45:42 amTrue, 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.

author: nctnico
author_rank: Super Contributor
timestamp: November 03, 2015, 12:20:44 pm
content: 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.

author: KE5FX
author_rank: Super Contributor
timestamp: November 03, 2015, 10:30:23 pm
content: Quote from: Wuerstchenhund on November 03, 2015, 12:01:45 pmYeah, 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.

author: AndyC_772
author_rank: Super Contributor
timestamp: November 04, 2015, 07:28:45 am
content: I'm not sure I see how a SA can really replace a time domain measurement.If I'm probing a high speed signal, chances are it's to see if it's monotonic, or perhaps to check the timing relationship between one signal and another. I can't remember any occasion when I've needed to simply measure rise time.

author: KE5FX
author_rank: Super Contributor
timestamp: November 04, 2015, 07:59:53 am
content: Quote from: AndyC_772 on November 04, 2015, 07:28:45 amIt's just a matter of whether you're doing more RF stuff than digital, or vice versa.

author: Rupunzell
author_rank: Frequent Contributor
timestamp: November 04, 2015, 06:09:14 pm
content: Very much a matter of what needs to be measured and done.Ghz time domain interments have evolved due to the need for Ghz digital that has become common today. These time domain instruments have their place and fills a particular need. Much the same can be said for frequency domain instruments. They offer a different means of measurement. Neither actually replaces one or the other once the measurement needs become more specific. Out of this appears the mixed domain instrument offering both time and frequency domain.. except it excels at neither as a result of inherent technology trade offs.Ideally one would have access to a really good time domain instrument, frequency domain instrument and a really good network-impedance analyzer for the specific range frequency spectrum range needed.Beyond this, skill, experience, knowledge, of the user makes all the difference in getting measurement results. Oh, there is also a host of adapters, cables and endless made up test fixtures and all that to make specific measurements required.BerniceQuote from: KE5FX on November 04, 2015, 07:59:53 am

author: Mosaic
author_rank: Regular Contributor
timestamp: June 03, 2016, 05:06:47 pm
content: While I have a 694c (1M, 1F,2F,13, HD) that stops displaying acquisitions on Ch3/4 on the main time base when triggered, it restarts and all else seems fine once Intensity is enabled with no chip mods. Also the thermal profile across the trigger chips with the case off is about a 50 °C delta after about 5 mins, with a 6° variance among the chips. I got the unit for $2k with a full cal. cert from Axiom test done for free because of the Ch3/4 issue, which I consider minor now, given it is sorted by a push button.While the discussion of which scope is better is healthy, for $2k a cal'd 3Ghz one shotter with glitch/ pulsewidth/logic and edge detection gives me capabilities I cannot afford otherwise in the wifi time domain. I use the analog 24xxA series ($300) for gen purp work and a Rigol DS2302A (cost $800 with full unlock) for other deeper memory slower DSO comm/SPI/I2C tasks. The 3 Ghz wakes up when frequencies of such interest or calibration type work for other scopes/instruments is required. It's just using affordable toolsets for the right app. A one device that does everything is great but $8K+ scopes are too much $$$. Also at >2Ghz , 50 ohm line impedance dominates and that is often RF Tx line related, at least for me.For $8K you can get a 3Ghz HP8753D VNA ($2k) , the 694C ($2k) , the Rigol Ds2302A unlock ($800) the 24xx Tek ($300), a Rigol 1.5Ghz -TG DSA ($1500), A 6.5 digit Rigol DMM ($600) with change for some good connectors, cabling , probes and such like.I am seriously considering adding a soldered on heat spreader to the heat solder pad under the TQFP trigger chips given the 1/2" clearance due to the PCB standoff for air flow. I note that Tek expressly ported the case to cool all the heatsunk chips with fresh air intake but NOT for these 4 trigger chips. Also I will reflow the pins on all the trigger chips as a precaution to 'stress relieve all the thermal & hygroscopic PCB changes over the years.Here is my cooling mod. project:https://hackaday.io/project/12087-tektronix-tds-694c-trigger-cooling-workaroundQuote from: KE5FX on November 01, 2015, 11:34:39 pm