old tek scope and some usb logic analyzer OR a $400-$500 new digital scope? - Page 1
Forum section: electronics / general

author: storkbus
author_rank: Newbie
timestamp: February 19, 2012, 09:37:01 pm
content: Like most here I'm on a small budget (monetary and time). I've decent tek 2225 scope. But I need more channels and I need to observe the various serial interfaces like i2c etc. For more or less the same amount of money I can buy a new Rigol or Owon. Both are extensively reviewed and discussed. A lot of bang for the buck but not perfect.Another route would be an old scope with a modern usb interface logic analyzer. A PC based logic analyzer is cheap and seems to be more than sufficient for microcontrollers and various buses like i2c. Of course the integration in a single device is nice but one pays a hefty premium such integration. And pay again for each separate protocol. So for the moment I think I'll buy a separate logic analyzer.The leaves the scope. To limit the playing field I've narrowed it down to two models. A tek 2465B (analog 4*400MHz) and a tek 460a (digital 4*400MHz). The 2465a is a well known good scope. But almost everyone requires a rebuild due to leaking condensators. No problem and well documented but takes a lot of time and costs money. But since it's analog what you see one the CRT happens at your probes. No missed glitches, no interpolation just the signal. But also no digital age handy features.Then I got an offer on a tek 460a with four original probes for $600. The tek 460a is fully digital. The specs are a bit lower than a 2465b from a quick comparison. But judging from the pictures and the lab from which it came give me the impression that this machine is in excellent condition and well maintained. And since it's much younger, 2001, no leaking condensators and higher life expectancy.What am I going to do with the scope? Mainly monitor signal quality on sender AND receiver at the same time to determine whether the timings are still within spec.Since I've no experience the tek400 series could anybody offer some hands-on experience on the scopes?Any opinion or advice about this topic is more than appreciated.Regards,Frederik

author: Unknown
author_rank: Unknown
timestamp: February 19, 2012, 10:10:38 pm
content: I would agree on the USB logic analyzer. The ~$150 bulk mode logic analyzers with almost unlimited memory are fine as long as you can live with the 24 MS/s sampling rate (should be plenty for slow buses like I2C). You can get more channels and a higher sampling rate in exchange for less memory with the FPGA-based designs, like the Intronix LogicPort and Zeroplus logic analyzers. Be sure to pay attention to the software, I personally really dislike the Zeroplus user interface, for example.Digital scopes are much nicer for digital signals in my opinion, since you can just trigger on a pulse and do a single shot acquisition. With analog scopes you have to arrange for a constant, periodic bit pattern, like sending a continuous stream of Us over RS-232. For analog signals analog scopes tend to be better than at least the old or low-end DSOs, due to their much higher update rate and intensity grading (which DSOs try to emulate, like the digital phosphor stuff). As for a Tek TDS-460a vs. a modern Chinese scope, the bandwidth and four channels are very nice, but the sampling rate limits the single shot bandwidth to maybe 40 MHz (according to Tek). Memory is less than modern DSOs, but 15 kpts is quite usable in my opinion. I haven't used a TDS-400, but comments about it seem fairly favorable. I think very few of the Chinese scopes are four channel, so your choice will become quite limited if you need this feature.I wouldn't be so sure that the TDS-460a is less likely to suffer from bad caps than the 2465b, plenty of bad caps in 2001, and I know several of the TDS-400/500 series scope fail self tests due to 'acquisition fail' because of bad caps. Don't know about the TDS-460a specifically, try searching the TekScopes archive.Why not start with the logic analyzer and see if you can manage with a two channel analog scope? The logic analyzer will do some of the tasks you might need those extra channels for, though not all. $600 is quite a hefty sum of change for something that you may or may not need and that may or may not meet your requirements.

author: kripton2035
author_rank: Super Contributor
timestamp: February 19, 2012, 10:46:27 pm
content: I was looking for a decent entry level logic analyzerI want to have the decoding of rs232, i2c spi, and if possible more like lin or can or usbbut these rigol digital scopes even with logic analyzer included dont do signal decoding.you need to spend a *LOT* more money to get this.so I'm keeping my analog scope (and small digital part) and I got a logic sniffer that's enought

author: storkbus
author_rank: Newbie
timestamp: February 19, 2012, 11:27:53 pm
content: @kripton2035 Thanks, that's what I found out as well. For some $130 I can buy a ZeroPlus analyzer and get 30 additional protocols for free.@alm Thanks for pointing out the software from ZeroPlus, I'll do some more research on the topic. One can tie the ZeroPlus to an Owon SDS series scope for triggering which I think is a nice feature. One reason I need a second scope is that I can place the one scope at the remote sensor and leave the other on the bench. If things don't work I just walk to the sensor(s) and have a look over there without disturbing my setup or hauling with many kilo's of scope.The offered scope has the extended memory and math option as well. And I misread the email, the tds460a is from 2003 and last calibration from 2007. The $600 is asking price.The seller send me a couple of pics from the interior. You don't want the replace the caps on these machines, there're way too many of them. But thanks for warning me. I didn't find any rebuild information like on the 2465b for example.I can drop two channels and don't really need the 400MHz. So that leaves me with the choice of a brand new DSO or a 10 year old tek460a. But the foresight of wasted time on firmware issues with a (too) cheap DSO isn't very attractive but a dead tek460a neither.Still any comments are more than welcome.

author: nixxon
author_rank: Frequent Contributor
timestamp: November 13, 2012, 12:01:38 am
content: I am waking up this old thread, as I am considering buying one of these scopes with options 05 13 1F 1M 2F.Quote from: alm on February 19, 2012, 10:10:38 pmAre you sure about this 40 MHz comparison?One of the highlights of the Tek TDS 460A is that:Capture Transient Events to the Full Scope Bandwidth with Its 100 MS/s Sample Rate(...)Capture Those Glitches with the 10 ns Peak Detect ModeDoes anybody know how this works in practice, compared to vintage analog scopes and recent digital scopes?Maybe this scope isn't that bad?Today I have a Rigol DS1102E and an old Tektronix 422 (15MHz).

author: Smokey
author_rank: Super Contributor
timestamp: November 13, 2012, 01:25:08 am
content: This "middle ground" price range of equipment, 500-1000 USD, always kind of amuses me. It's kind of no mans land for non-professionals. It's relatively easy to justify something cheaper to just play with, and if you actually need something more expensive for a specific job or something then that's easy to justify too. But you can get stuck agonizing over that damn 500-1000 price range. Unfortunately a fair amount of what used to be high quality top end gear that you can now find used falls into that range too.One thing to keep in mind is how much DSO tech advanced and how fast. I would relate it to the iphone. The first iphone was released in 2007. That was only 5 years ago! As far as functionality the first iphones were great at the time and still decent now, but if I made you use an original iphone as a daily driver after you got use to modern phones it would drive you crazy. While you could probably make it do most of the basic stuff you wanted these days, being relatively speaking crazy slow and lacking the modern features/memory would probably be a deal breaker. It's the same deal with DSOs, and a lot of them are more than 5 years old.If you are thinking of buying something used in the "no mans land" 500-1000USD range then you should remember that you can quickly outgrow what used to be top end gear too since compared to modern tech they now look like dinosaurs. The sample rate (like 100Ms/s) is only at the fastest timebases, and it goes down really fast. The only thing worse than fighting with a circuit is fighting with your test gear. I'd say stay out of the no mans land. If you can get by with something cheaper for the foreseeable future, do that. Otherwise save up for something nice. Or get something super cheap now AND save up for something nice.A cheap DSO and cheap logic analyzer should get the job done most of the time. Once you have an actual performance requirement that the cheap stuff can't meet, then the decision is MUCH easier. Especially if you saved the money you would have spent in "no mans land."For that Tek 460, how do they claim 400Mhz bandwidth out of 100Ms/s? Is it one of those averaging deals? I didn't read the manual

author: nixxon
author_rank: Frequent Contributor
timestamp: November 13, 2012, 08:33:12 am
content: Thank you for your reply. I am glad I found this thread.I found the relevant info:http://www.tek.com/document/application-note/real-time-versus-equivalent-time-samplingBy using DSOs with higher sample rates one can acquire higher-bandwidth signals in real-time. For example, an engineer wants to acquire and store a single-shot 50 MHz signal. Using a scope with a 400 MHz analog bandwidth and a 1 GS/s sample rate, creating a real-time bandwidth of 400 MHz, he can easily acquire the signal in real-time.However, if the engineer chooses a digital scope with an analog bandwidth of 400 MHz and a 100 MS/s sampler, he cannot accurately acquire the 50 MHz signal in real time. Although this scope, like the first one, has an analog bandwidth of 400 MHz, its maximum sample rate of 100 MS/s limits the real-time bandwidth to only 40 MHz.Even if the 460A captures 10nS glitches over a wide timebase range, it seems no better at this than a 50 MHz Rigol DS1052E with a 1GS/s sample rate.I tend to believe that a 400MHz analog scope like the Tektronix 2465B is more useful than the 460A. (both 4 channel scopes). Now I consider getting a Philips PM 3244 (analog 4 channel 50 MHz), that the seller wants to sell for US$ 165, rather than the 460A that the seller is reluctant to sell for US$ 500.