Looking for high bandwidth (>4 GHz)used or older scope recommendations - Page 1
Forum section: electronics / testgear

author: JohnG
author_rank: Frequent Contributor
timestamp: September 20, 2018, 03:21:02 pm
content: Folks,I have a chance to purchase a used Lecroy Wavemaster 8620 for what seems to be a decent price. I have used other Lecroy scopes in the past, such as the LC574 and Waverunner 6100, so I know what I am getting into with the interface. What I am looking for is whether or not the scope has any big problems to watch out for. I have a chance to spend an hour or two looking at the scope before I decide.Any help or advice appreciated. Other scope recommendations for similar scopes are also appreciated.Thanks,John

author: DaJMasta
author_rank: Super Contributor
timestamp: September 20, 2018, 04:30:04 pm
content: Don't know about the 8620 specifically, but I've got a WavePro 7200 and by the look of the specification, a lot of parts are probably similar to the 7000 line. The interface should be as you expect, since the X-Stream software goes back for a while, but the datasheet I saw mentions Windows 2000, which would mean you're limited to upgrading the software to version 6.8 or something - if you install XP on it, you then get access to more recent revisions of the software, which I believe do officially support this scope (maybe not the newest versions, but version 8.something, at least).You probably already know if you're looking into this bandwidth, but you're going to need ProLink adapters just to get an SMA connection on an input channel, and those high bandwidth probes do not come cheap and if you buy used, often don't come with accessories. Also worth mentioning the frontend is only good to +-4V, so treat it gingerly!From the spec, looks like the edge trigger is only available to 5GHz, not the full 6GHz of the unit, and the fancy SmartTrigger options are only available to 750MHz.Otherwise, the layout is probably similar to a lot of their scopes from the mid 2000s, so you'll probably have an off the shelf mATX board as your computer and a regular hard drive mounted to the back chassis - so upgrading to get a bit more compute performance or lower loading times is probably easy.

author: joeqsmith
author_rank: Super Contributor
timestamp: September 21, 2018, 01:35:12 am
content: I have the WM 8500A. In general, I like the scope and can't think of any major problems off hand. I did increase the RAM, added an SSD, added a 1G Ethernet card and switched from Windows 2000 to XP.What accessories does it have? Adapters, probes?

author: Proto
author_rank: Contributor
timestamp: September 21, 2018, 07:13:10 am
content: Keysight has an eBay storefront that offers 2 types of products for the secondary market, premium and used. Both are refurbished but premium carry the original warranty and have all new probes, manuals and standard accessories. Used have the biggest discount off list but come without standard accessories and a reduced warranty. Either category may have instrument options installed. There are S-Series (up to 8 GHz) and 6000 X-Series (up to 6 GHz) units there now. Ending soon, the 6000 X-Series units include Keysights extensive apps bundle and have tremendous discounts.

author: LapTop006
author_rank: Unknown
timestamp: September 24, 2018, 07:17:58 am
content: Quote from: Proto on September 21, 2018, 07:13:10 amIndeed, I bought one of the 6000-X combos recently (hopefully being delivered this week). I avoided the S-series due to desktop Windows.Earlier this year I was planning on a combo of a new lower bandwidth scope & and older multi-Ghz scope (likely an older Tek DPO7000), but the 6000-X was a good enough deal that I picked it up.A key thing to consider whatever you plan to buy is probing, above the level reasonably priced passive probes work (500Mhz or so) probes get *very* expensive very quickly, and you need to be careful about understanding what loading they cause. Active probes can be easy to damage and many sold on eBay are.

author: Berni
author_rank: Super Contributor
timestamp: September 24, 2018, 07:25:29 am
content: Do not forget about probes indeed.Anything above 500MHz makes a active probe pretty mandatory and these kind of probes can be really expensive. To make it even worse the scopes only work with active probes from the same manufacturer and a certain scope might not support all types of probes.Once you see the sort of performance you get with these probes you start to use them even for anything above 50MHz as you can get excellent signal quality even with huge long ground connections while the DUT barely even noticed the extra loading from the probe.

author: joeqsmith
author_rank: Super Contributor
timestamp: September 24, 2018, 10:56:30 am
content: I have some Lecroy resistive probes that are good for over a GHz. My PP066 is rated for 7.5G. I've also made several resistive probes. Still, at least in my experience, my home made probes have never been good for much over 1.5GHz. No where near what the OP is wanting. For digital work, I have a few active differential probes.More to your point, I could see someone spending more on the probes than on the antique scope. No idea what the OP is needing the scope for but I assume they have the probing part sorted out.

author: Berni
author_rank: Super Contributor
timestamp: September 24, 2018, 11:45:09 am
content: I did make some DIY high speed probes that worked just fine even at 3GHz, but thy ware 10x probes with under 1 KOhm input impedance at DC. Its basically a heavily mismatched attenuator out of 0402 resistors on the end of a 50 Ohm coax. Worked well enough in a pinch for probing at RF stages. But its still not really a practical general purpose probe, this was designed to poke 50 Ohm things without upsetting the 50Ohm-ness of it too horribly due to capacitance.But in terms of scope, most cheap scopes in that range will be old Windows based scopes. And that's not really that bad, they are indeed kinda slow and clumsy to set up, but that's partly due to how much functionality is packed into them. They are great for doing that careful specialized measurement of something, but for the daily driver still keep around a normal few 100s MHz scope. They have more resilient inputs that are harder to blow up and in general are quicker to operate for simple tasks like checking if a clock signal is present or checking if a SPI bus is doing stuff.

author: joeqsmith
author_rank: Super Contributor
timestamp: September 24, 2018, 12:45:33 pm
content: 3GHz is impressive on a home made resistive probe. Anything I have built goes into the crapper well below that.Above a GHz, I am not sure what a general purpose probe would be. LeCroy used to offer a buffer for the scope the OP is looking at. I made a simple one for mine that gets me into the 100MHz'ish with a 10X probe. It's come in handy but like you, I normally don't use my higher speed scope for my data to day use.My oldest DSO has 4GHz BW. I still use it when I am playing with high voltages.https://youtu.be/WXFoAAL7hxo?t=929

author: nctnico
author_rank: Super Contributor
timestamp: September 24, 2018, 02:39:11 pm
content: I have some Tektronix P6156 passive divider probes and these work up to 3.5GHz in x10 (500 Ohm) or x20 (1k Ohm) mode. These aren't wildly expensive when bought from Ebay.

author: Berni
author_rank: Super Contributor
timestamp: September 24, 2018, 04:58:01 pm
content: Yeah such passive probes use that resistive divider trick that i used, the problem is that they have pretty low impedance at DC while an active probe will give the same low input capacitance while still being 100K Ohm or above so it loads down the DUT as little as possible. I have gotten into a habit of using active probes for general purpose use just because the signal looks perfectly clean even with 20cm of ground clip thanks to next to no current flowing into it during sharp transients.I only tested my bodged together DIY probe to 3GHz because that's what the network analyzer i was using it on went to, i was actually using them at around 1.5 GHz but swept them from 0 to 3 GHz to be sure its reasonably flat. You can get pretty good RF performance out of 0402 resistors due to there small size keeping the parasitics fairly in check, i also built a 3 port SMA resistive power splitter out of 0402 resistors and that was nice and flat to 3GHz too with a good VSWR.I do have some 20GHz RF gear at home where i could try measuring it higher but that DIY probe was built for just a single task of tracing down a fault in a RF chain, it was not meant to be anything good, but it turned out good enough to keep in the RF drawer in case i need to poke around RF stuff with no test ports.