Inexpensive >=2GHz scope (ETS ok!) - Page 1
Forum section: electronics / testgear

author: timbojames
author_rank: Contributor
timestamp: July 16, 2019, 01:49:12 pm
content: EDIT_FINAL: You can see my original query below. I'm reviving this because I did get in touch with Sabanovic after posting this; he had just been out of the country at the time. He was extremely helpful and I did get one of his DS800 scopes. It has been working great for us so far and meets all our requirements. I know he's making an attempt to get back behind his USB scopes, so I wanted to add this edit in case this post winds up in someone's search.I'm new to the forum but have lurked around here for several years. I'm in need of oscilloscope with at least a 2GHz bandwidth (will be working with 915MHz ism bands and lower). Equivalent time sampling is perfectly ok.I've already tried the eBay used scope avenue. I've received three different scopes (Tektronix models) with various failures not reported by the sellers. Its brutally obvious that people are snatching these aging scopes up at auctions and selling them as 'working' without knowing the first thing about how to verify they are actually working. This has taught me to use much greater scrutiny on listings and the listings where I'm confident the scopes have actually been tested (knowledgeably) tacks on an extra $700-1000USD on the price. I'm familiar with the component aging issues on most of the used high bandwidth scopes, but I just don't have the time to pick up a bunch and try to work on recapping the boards.I thought I had found an alternative in Sabanovic's DS800 USB scope. It's a high bandwidth equivalent time sampling scope which is perfect for my needs and fit in my STRICT budget of <1500 USD. Maybe everyone here already knows this, but the fellow is AWOL. I even tried to buy through his website and the transaction in PayPal has sat as 'pending' for over a week. No response to emails either.I have failed to find any product similar in performance or price to the DS800. Again, I need something up to 2GHz bandwidth, 2 channels minimum, equivalent time sampling is perfectly fine at a price of <=1500 USD. I know plenty of people have done their own DIY projects to build things similar to the DS800, but this isn't a viable alternative for me. Used equipment is fine, but I'm incredibly tired of returning scopes on eBay. eBay is the only option I know of at the moment so I'm continuing to pursue it. I also don't live in an area where used scope are available for physical purchase in person.Just FYI, this oscilloscope is needed as a stopgap instrument for a start up venture so that we can get enough data to secure some funding. Unfortunately that means we need it asap and it needs to be cheap. I'm sure some of you can understand that predicament.Thanks in advance for any help or guidance.EDIT: Since I'm getting a lot of 'a scope is not what you want' argument, let me clarify that the 915MHz band that we are interested in is not a carrier. There is no modulation. This is not a communication/data signal in any traditional sense. The most critical thing to measure is the phase relationship between a signal and master clock/trigger all operating around 915MHz (this is an intentional delay used as a tuning parameter that must be controlled). I anticipate needed to see up to the third harmonic which makes my bandwidth need shift more into the 3GHz range minimum. A spectrum analyzer would definitely be a nice to have, and will be a necessity later, but we can't afford both yet.

author: tggzzz
author_rank: Super Contributor
timestamp: July 16, 2019, 02:17:18 pm
content: What you haven't said is what measurements you intend to make at 915MHz.Frequently a scope is the wrong tool for RF measurements. I haven't yet come across a use-case for using a scope to look at an RF signal of the type you would find at 915MHz.

author: timbojames
author_rank: Contributor
timestamp: July 16, 2019, 02:34:03 pm
content: Quote from: tggzzz on July 16, 2019, 02:17:18 pmUnderstandable, but we would not think we had a good technology for a startup venture if we didn't have some unique IP. Suffice it to say that a scope is the right tool for us right now. That's not to say down the road when we can afford a full instrumentation arsenal that other instruments wouldn't be of tremendous value. We obviously can't afford that at the moment, and we would be happy with a scope that can view and measure voltage wrt time on repetitive signals up to 915MHz.

author: tggzzz
author_rank: Super Contributor
timestamp: July 16, 2019, 03:06:10 pm
content: Let me ask the "what measurements you intend to make" in a different way:what ENOB do you require for your application?will the non-linearities in fast ADCs affect your measurements?

author: DaJMasta
author_rank: Super Contributor
timestamp: July 16, 2019, 03:11:13 pm
content: Also what sort of bandwidth you need. The advantage of a scope is that you have ALL of the bandwidth available for analysis, the advantage of a spectrum/signal analyzer or similarly architectured instrument is that you have dramatically increased sensitivity and lower noise floor. Because RF signals, especially received ones, tend to be very small and modulation schemes tend to be narrower band (they have to be to fit International/National regulations), getting a SA with enough demodulation bandwidth for your signal is generally a better choice to get measurements of your signal.If you do end up needing a scope, often the best price per GHz on the used market is LeCroy scopes. Some people don't like them, but I've had good experiences and you can sometimes get working ones of a reasonable vintage for less than $1000/GHz, and they've been discussed at length in some similar threads and elsewhere.

author: edavid
author_rank: Super Contributor
timestamp: July 16, 2019, 03:17:42 pm
content: So just rent a scope. I think you will quickly realize that it's the wrong instrument, as everyone is telling you.

author: timbojames
author_rank: Contributor
timestamp: July 16, 2019, 03:34:23 pm
content: Let me preface this by saying I'm not an RF Engineer, I'm not even an EE, I'm an ME. I have a fair bit of experience with test equipment, but nothing in this kind of frequency range. Over the past year I've been forced into these waters based on how our theoretical constructs developed.Our 'requirements' are hard to define at the moment since so much of our work resides in computer simulation and what we need to further analyze are going to be real world implementation phenomena. What those phenomena are going to be and what we will need in order to analyze them is impossible to say right now.It's easy enough to say a 12bit ADC ought to suffice. If I had to put a value on ENOB I'd say we'd be pushing our luck to expect more than 5-6 at this price range at our frequency of interest. Maybe even that is wishful thinking. I do not think the non-linearities are going to affect us too much. We are after qualitative understanding at this stage in the game, not quantitative accuracy. At some point the quantitative accuracy starts to affect the qualitative results though.I appreciate the thoughtful queries into our needs. I wish I could say more, but there's plenty of unknowns and plenty I just can't go into detail on. We are at the baby steps of actually building any kind of real world implementation. Computer simulations aren't enough. So it's a bare minimum kind of demonstration out of our own pocket.

author: timbojames
author_rank: Contributor
timestamp: July 16, 2019, 03:37:09 pm
content: Quote from: DaJMasta on July 16, 2019, 03:11:13 pm2GHz really is enough bandwidth. If someone made a 1.5GHz scope that would be enough bandwidth. Believe me I know how 'wrong' that sounds for a 915MHz band signal. LeCroy recently hit my radar as a brand that tends to run a little cheaper than the Tektronix/Agilent models. I've currently been focused on those.

author: timbojames
author_rank: Contributor
timestamp: July 16, 2019, 03:43:41 pm
content: Quote from: edavid on July 16, 2019, 03:17:42 pmWe've gotten a handful of rental quotes. Given our lowest estimate of the duration we will need it, we grossly exceed the $1500 budget. I have had very poor luck finding available rentals of the old equivalent time sampling scopes. Which means what is available to rent rapidly exceeds our budget. If you're aware of shops renting out an ETS scope with at least 2GHz bandwidth for $200-300 a month, then PLEASE let me know of them.I know everyone thinks it's the wrong tool. I just can't explain in gross detail why it is the right tool. Take my word on it, even if you're utterly convinced we will be wasting our money.

author: nctnico
author_rank: Super Contributor
timestamp: July 16, 2019, 03:58:09 pm
content: Quote from: timbojames on July 16, 2019, 03:37:09 pmLook for the Agilent 54835 and uphack it to the 54845 (by changing a few resistors) to get a 1.5GHz scope. Lots available as 'for parts' units; ones with a sticker saying VIN33 are the newest. Since you seem to be measuring in a narrow band the frequency response won't matter that much I guess. Lecroy is also a good option.

author: 0xdeadbeef
author_rank: Super Contributor
timestamp: July 16, 2019, 04:00:43 pm
content: The Tektronix tds7254 is sold around 2k€ at eBay now and then - but usually without any probes or even the TCA-BNC adapters.I don't recall ever seeing any LeCroy >= 2GHz being sold for something even close to this price race.

author: edavid
author_rank: Super Contributor
timestamp: July 16, 2019, 04:10:34 pm
content: "I'm not even an EE" + "take my word on it" doesn't really add up.Why don't you develop your technology at a lower frequency?Or post a want ad over in Buy/Sell/Wanted? I'm sure some hobbyist will rent you a sampling scope for $1500.

author: tggzzz
author_rank: Super Contributor
timestamp: July 16, 2019, 04:33:45 pm
content: Quote from: timbojames on July 16, 2019, 03:37:09 pmLet me ask some other questions.If you have an audio signal (i.e. <20kHz) that is amplitude modulating a 915MHz carrier,at how many GS/s do you need to sample the 915MHz carrier in order to see the amplitude variations?what jitter spec do you need for the trigger signal?

author: woodchips
author_rank: Frequent Contributor
timestamp: July 16, 2019, 05:36:30 pm
content: Almost any sampling scope by Tek or HP will do 1GHz. The biggest problem is that other than the 7T11 they all also stop triggering at 1GHz but the sampling input is wide open and will happily display 4GHz signals, reduced amplitude of course, but still be there.The 7T11/7S11 are the newest, but the ones for the 560 series Tek scopes or 180 series HP scopes will all do. It is just finding one and looking at it being demonstrated.The 7401 scope will do 1GHz, just seen two of these sell for less than £100 each, with the correct plugins, in the last couple of weeks.Sometimes this older stuff is so much better than the newer stuff.

author: timbojames
author_rank: Contributor
timestamp: July 16, 2019, 05:42:42 pm
content: I'm sorry that I'm dealing with a proprietary technology that I can't go into depth on. You guys are thinking like signal engineers and in light of that, what I'm saying sounds silly, I get it.I'll say this much. There is no modulation and there are specific laws of physics reasons that we are interested in a 915MHz ISM band. This isn't a communication signal, it's not a carrier. I get that everyone wants to tear me apart considering what I've asked, but you're actually assuming a lot that isn't accurate. This is not a typical use case.I was merely hoping someone knew of some alternatives to the avenues I was pursuing in trying to find a used scope or someone knew of a not well marketed device that I had missed.

author: DaJMasta
author_rank: Super Contributor
timestamp: July 16, 2019, 05:45:08 pm
content: Quote from: timbojames on July 16, 2019, 03:37:09 pmNot exactly what I mean by bandwidth - the scope will digitize the entire bandwidth from DC to its maximum including your signal of interest, but if you're doing any kind of RF work, the only bandwidth you'll likely be interested in (at least in the time domain) is the channel around your carrier frequency, so if your 915MHz signal operates on a 40MHz channel, you really only need to look at 895MHz to 935MHz to get information on the content of your transmission. It's helpful to see otherwise, sure, below and above gives you spurious emissions and whatnot, but especially with an 8 bit converter in a scope, you're not going to pick up small ones anyways.So if you're looking at the content of the signal, you really need a mixer and an LO source (an RF signal generator) to downconvert your 915MHz signal to be digitized on a much lower bandwidth device, or you want an instrument that does this on its own as a spectrum analyzer with an IF output or with signal analysis capability. The advantage of the spectrum analyzer is that even a relatively standard 3GHz bandwidth will give you the second and third harmonic of your signal, which will help diagnose spurious emission issues with it.Worth mentioning that sampling scopes aren't great for RF transmission work, since you'd have to retrigger on the packet being sent and then send the packet hundreds or thousands of times to get it to fully show on the scope display, which requires some low level hardware control since most protocols take care of retransmission automatically.As for the price, maybe it's harder to find cheap LeCroys overseas, but All the ones I've dealt with have been <$2000 for a 2GHz scope (they are sold for over, but I don't bother at those prices), I've got one that needs a new bezel that I'll be sending off at some point for that price point, and I still don't think it's the right instrument for most RF work. I'd be looking at a 3GHz SA with TG for a 915MHz RF transmission and characterization of the signal or diagnosing of transmitter issues.BTW, to digitize a 915MHz carrier with a 20kHz modulating signal, you need 1.83004GS/s assuming standard AM - the lower frequency content doesn't require any special sampling speed since it's much, much slower variations in the carrier.

author: Datman
author_rank: Regular Contributor
timestamp: July 16, 2019, 05:56:42 pm
content: That's all right. A 2GHz scope let you see only the fundamental at 915MHz, the 2nd and the 3rd harmonics. I think it would be more useful a 3GHz or 6GHz spectrum analyzer and a 50 (100) MHz digital scope like the classic, cheap Rigol DS1054Z with many free math functions for analog and digital signals!

author: tggzzz
author_rank: Super Contributor
timestamp: July 16, 2019, 06:50:12 pm
content: Quote from: DaJMasta on July 16, 2019, 05:45:08 pmAbsolutely not, and that was the point of the question.

author: tggzzz
author_rank: Super Contributor
timestamp: July 16, 2019, 06:54:18 pm
content: Quote from: timbojames on July 16, 2019, 05:42:42 pmThat changes nothing. The maths works whatever you call it.

author: Jwalling
author_rank: Unknown
timestamp: July 16, 2019, 07:15:55 pm
content: Quote from: nctnico on July 16, 2019, 03:58:09 pmIn the OP's price needs, I'd second that; or just get a 54845A. Another option might be a TDS794D, but there's not many around...Not too bad...https://www.ebay.com/itm/182282000068?Ask the seller if it passes SPC and the FULL self test from the utility menu!EDIT: But then again, you can get 8GS/s on the 54845A on 2CH. I think I would choose the 54845A.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 16, 2019, 07:24:15 pm
content: Quote from: timbojames on July 16, 2019, 01:49:12 pmI will admit, when I saw your original post this is first thing I thought. I wouldn'tsay people are berating you. You asked for advice, people gave it, and it just didn't align with the answers you were expecting.I'm amazed at some of the prices I will see on used LeCroys. I have a few vintage ones. The oldest has a 4GHz BW and uses RIS which is fine as many times I am looking at repetitive signals. These old relics can be found for well within your budget. I gave one away a while back.You may require a faster one-shot rate. In that case, I would start searching the used market. You may find something in your budget that would meet what ever your requirements are. Some sellers will offer a trial to insure the product works once it arrives. With these old scopes, consider if it doesn't work, the manufacture may no longer service it. If they do, that service may very well cost more than your entire budget. Not to mention your time.Good luck with your new business. Hope it goes well for you.

author: bdunham7
author_rank: Super Contributor
timestamp: July 16, 2019, 11:08:05 pm
content: Quote from: timbojames on July 16, 2019, 01:49:12 pmCan you tell us what aspect of the signal you do need to look at and what amplitudes or other characteristics it will have or that you will be looking for?

author: timbojames
author_rank: Contributor
timestamp: July 16, 2019, 11:55:32 pm
content: Quote from: bdunham7 on July 16, 2019, 11:08:05 pmI ran back into some HFSS/Maxwell simulations and I admit I mispoke by claiming I only needed 1.5GHz bandwidth. We may need to see as high as the third harmonic so really even 2GHz is going to be pushing it, but again we just don't know and we are on a budget. The 8GHz TDS820 seemed like a perfect option until we ran into a slew of bad sales of defective scopes. We will generally be interested in simple amplitude and phase measurement off a master clock/trigger. However, there is going to be a lot of unforeseen distortion to the base signal because of the test apparatus and the next most important thing is to be able to visualize that distortion so we can systematically identify the cause and clean it out of the system. For the purposes of this discussion you could consider the base signal sinusoidal.

author: tautech
author_rank: Super Contributor
timestamp: July 17, 2019, 12:55:10 am
content: Quote from: timbojames on July 16, 2019, 11:55:32 pmLike the others said, a SA is the right tool for that.A 2.1 GHz SSA3021X comes in right on budget.https://www.siglentamerica.com/spectrum-analyzers/ssa3000x-series-spectrum-analyzers/

author: timbojames
author_rank: Contributor
timestamp: July 17, 2019, 04:43:05 am
content: Quote from: tautech on July 17, 2019, 12:55:10 amSpectrum Analyzer would be nice, but we can't afford both and it's critical to see phase relationship between a signal compared to a master clock/trigger (there is some intentional delay that must be controlled). The distortion/artifacts/reflections are going to be a fact of life and we'll have to do the best we can with a scope to analyze those because for the interim we can't buy both. Hence the scope needing enough bandwidth to hit the second harmonic bare minimum, preferably the third.I've been looking at these LeCroy Disk Drive Analyzers because it seems they can be found for about 1.5-2k USD and they have a 5GHz -3db bandwidth and good sampling rates. Reading through the manual, they appear to just be an oscilloscope with some specialty functions for disk drive analysis.

author: OwO
author_rank: Super Contributor
timestamp: July 17, 2019, 04:56:50 am
content: No, no one here seems to be getting the OP's point, so let me ask you this:Do you have to be able to see the signal's waveform? If so then a SA absolutely will not do.A SA will NOT tell you the relative phase between the fundamental and the harmonics!This is what ETS scopes are for, and if that is truly the use case then people can stop suggesting a SA based solution!

author: joeqsmith
author_rank: Super Contributor
timestamp: July 17, 2019, 05:00:56 am
content: Like this?https://www.ebay.com/itm/LeCroy-DDA-5005A-XL-4-Channel-Disk-Drive-Analyzer-WaveMaster-8500-Oscilloscope/153444975958?epid=1617668161&hash=item23ba088556:g:6ksAAOSwRW9cq-eh1.5K would be a very good price for a working one with accessories. A few people here have been upgrading them with new screens and MBs. You shouldn't have any problems finding help if you have questions about it.

author: hendorog
author_rank: Super Contributor
timestamp: July 17, 2019, 08:05:18 am
content: It sounds like you don't actually need much bandwidth.So could you downconvert both signals it to a more sensible frequency using two mixers and some cheap PLL board from ebay.Then use a basic scope such as the Siglent 1000XE series to monitor the phase relationship. It will be the same at baseband as it is at 915MHz.And it has an excellent FFT which you can make use of for the distortion monitoring.Get your funding that way and then buy the real deal gear.There are other ways to do it which are cheaper, but it sounds like you need something which produces pretty pictures as well as being able to be explained.

author: Mechatrommer
author_rank: Super Contributor
timestamp: July 17, 2019, 08:11:13 am
content: Quote from: timbojames on July 16, 2019, 05:42:42 pmQuote from: timbojames on July 17, 2019, 04:43:05 amfrom the sound of it, you want something greater than 915MHz fundamental, something 10X BW than that to see analog nature qualitatively of the signal, and 10X the sampling rate to see some phase difference between 2 signals, and even that, some type of "physics" will not accept that minimum limit (only 1/10X jitter tolerance compared to a period of the fundamental). at your budget and spec, i think you are looking at 20GSps because thats what still available cheap in used market, above that the price immediately sky rocket. maybe Lecroy 3 - 6GHz Wave Master / Pro / SDA / DDA series may suits you at currently affordable budget (200GSps ETS). or maybe are you talking about 91MHz? and want to see the quality of it? with 1-2GHz, all you see is 915MHz sine wave with differing amplitude and jitter spec / phase difference limit dictated by the sampling rate or ETS. ymmv.

author: timbojames
author_rank: Contributor
timestamp: July 17, 2019, 09:05:01 am
content: Quote from: joeqsmith on July 17, 2019, 05:00:56 amThat is what I was eyeballing. Connectors seem to be an annoyance but I've already seen people circumvent the $300 adapters.

author: timbojames
author_rank: Contributor
timestamp: July 17, 2019, 09:14:29 am
content: Quote from: Mechatrommer on July 17, 2019, 08:11:13 amIts two independent tasks. I need to be able to set an accurate delay by looking at phase of a 915MHz pure tone. Second test involves looking at the 'result' (which will have distortion) and to qualitatively get a look at artifacts that I anticipate will be in the second (and possibly third) harmonic range. I know accurately viewing a third harmonic isn't going to happen on a 2GHz scope, I've admitted I fudged that spec. I really need something in 3-4GHz range with suitable sample rates (depending on the sampling scheme used). We at least aren't concerned with accurate phase measurement in that third harmonic range, that's all taking place with the 915MHz unadulterated pure tone. I'm well aware the instrument is going to be a limiting factor, but as you said the price skyrockets to go 10x which is where everyone wants to be.The LeCroy DDA5005A that we referenced above can do 200GS/s with RIS.The only thing I meant by 'laws of physics' was someone suggested I do the demonstration at a lower frequency. There's reasons various technologies use the frequencies that they do and what we are pursuing is only practical logistically and physically with a 915MHz ISM band.

author: Mechatrommer
author_rank: Super Contributor
timestamp: July 17, 2019, 09:33:26 am
content: if you wait patiently, or get creative you can get used 3-7GHz differential probe for it at around 500 - 700 USD... i collected 3 of these probes during a span of time waiting and stalking and offering at less than 2K. get creative i mean you look separately head and body/adapter that each seller cannot test, so they sell it as is... bargain has becoming more difficult lately but maybe with best offer you can still get at the ballpark price, dont ever expect them to be like rigol probe kind of cheap though, even the active (non differential) ghz probe type.https://www.ebay.com.my/itm/New-Teledyne-LeCroy-Wavelink-D500PT-6GHz-Differential-Probe-in-cal/323745468566?hash=item4b60bbd096:g:n10AAOSwtfhYnzETpeople are working on diy BMA to BNC/SMA adapter at low cost alternative... and/probably later the diy active/diff probes... for agilent brand i'm not sure, they are $1K tag for 1-2GHz diff probe i currently see in ebay.. some agilent or tektronix stalker may give you better advice..

author: nctnico
author_rank: Super Contributor
timestamp: July 17, 2019, 11:16:41 am
content: Quote from: timbojames on July 17, 2019, 04:43:05 amIf you want to see the phase relationship then I recommend looking at the Agilent 54835, 54845 or 54846. These have a higher resolution trigger interpolator so you can measure the phase relationship with a higher precision. IIRC the Lecroy scopes in your price range typically have a lowest time/div of 200ps and the Agilent scopes allow 100ps/div.For looking at distortions spectrum analysis is a better tool. This is available on the oscilloscopes mentioned so far (FFT) but using a spectrum analyser you can get more bandwith and a better frequency resolution for less money.

author: Berni
author_rank: Super Contributor
timestamp: July 17, 2019, 12:55:54 pm
content: You can get a 20GHz sampling scope for under a grand if you are lucky enough around the used market, something along the lines of this:https://www.keysight.com/en/pd-54751A%3Aepsg%3Apro-pn-54751A/20-ghz-dual-channel-electrical-moduleBut as people have said if you only need it for one special measurement then it might make more sense to rent something like this from an equipment dealer.

author: timbojames
author_rank: Contributor
timestamp: November 08, 2019, 06:14:02 am
content: Added a final edit on my original post for the sake of Darwin Sabanovic who was extremely helpful once I got in touch with him. I did get one of his DS800 USB scopes and it has been working great for us for the past couple months. Thanks to everyone else for your advice and guidance as well.

author: ZhuraYuk
author_rank: Regular Contributor
timestamp: November 08, 2019, 01:40:16 pm
content: Quote from: timbojames on July 17, 2019, 04:43:05 amBe aware that those have only 50 Ohm inputs. I recommend to go for used LeCroy WavePro 7100A. It is fully hacked and bandwidth limit can be unlocked to 3Ghz by removing capacitors and replacing resistors in front end (rest of the hardware is incidental across all 7000 series). Inputs are 1M/50Ohm switchable in all bandwidth range.