Medium-bandwidth oscilloscope probe recommendations? - Page 1
Forum section: electronics / testgear

author: ethereal
author_rank: Contributor
timestamp: September 05, 2014, 07:35:18 am
content: Hello everyone,Just having purchased a used oscilloscope off of eBay, I'm now faced with the dilemma of finding probes for it. I'd rather not spend more than strictly necessary, but it seems a shame to ruin a decent oscilloscope with cheap probes. I originally decided I wanted a scope after realizing that a transient fault in a board was due to interference between two circuits on the same PCB. (Poor routing on my part, but I'll probably make the same mistake again . . .) I eventually found it with a logic analyzer, but I'm hoping that with an oscilloscope these things will be more immediately obvious.So: I've read thethreadon the cheap P6100 probes off of eBay, which are seriously tempting. However, the scope I purchased has a rated bandwidth of 500MHz, and I'll be using it on digital circuits with clocks in the range of 30-100 MHz. As such I'd really appreciate having the full 500MHz bandwidth supported in my probes. I was thinking about going for some ofthese "500MHz" P6500 probes. I haven't been able to find any reviews of that particular model yet, though, so I'm a little leery of buying them.Of course, I could also go the route of buying high-quality probes from, say, Agilent (or used versions thereof) but by the looks of things I'd be paying almost as much for each probe as I did for the entire scope in the first place. If possible, I'd rather save my electronics budget for components!I'm also wondering about grabbing some lower-frequency probes (I've seen four of the P6100s on eBay for $25 USD). Is it a "the more, the merrier" type of situation?If anyone feels like weighing in on the subject, I'd be most appreciative. Thanks!- ethereal

author: tautech
author_rank: Super Contributor
timestamp: September 05, 2014, 08:02:02 am
content: First grab some cheapies for "everyday" work. The P6100's are perfectly OK.That way you are "up and running".Then you can take your time to find those you might be happy with and fit your budget.For any high speed work you will do, you might only need 2 x 500 MHz probes.Expect to spend up to US$100 ea for good quality 500 MHz probes.

author: VK5RC
author_rank: Unknown
timestamp: September 05, 2014, 08:21:14 am
content: +1 for some cheap every day probes, i have some of those 6100 and am happy, I keep my good sets (came with the scope) for when the "going gets tough " and you need the absolute bandwidth /impedance.

author: tggzzz
author_rank: Super Contributor
timestamp: September 05, 2014, 08:24:53 am
content: You should do some research into the differenttypesof probe before hunting for individual examples. It certainly isn't a case of one-size-fits-all.Match the probe to whatever you are testing -the probe is part of the circuit! Understand the effect of probe tip capacitance and ground lead inductance. Hint: if you have a *10 probe what's the load it imposes on the circuit at 10/100/500MHz. Hint: what's the self-resonant frequency of a probe with a 6" ground lead.Consider making your own low impedance (500ohm) probe, if it matches your requirements.

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: September 05, 2014, 09:12:49 am
content: Quote from: ethereal on September 05, 2014, 07:35:18 amCongratulations. Just curious, what scope did you buy?QuoteIf you want to utilize the full bandwidth you should really consider active probes. Passive divider probes are only really good to say below 300MHz no matter what the sticker says.So if I were you I'd do as other suggested and get a set of cheap passive probes anyways as they are still useful for tasks that doesn't require high bandwidth. In addition, I would have a look at suitable (for your scope) active probes. Active doesn't necessarily mean expensive if you're patient. For example, I bought an active 500MHz AP033 probe for my LeCroy scopes for roughly $85 + shipping.

author: tggzzz
author_rank: Super Contributor
timestamp: September 05, 2014, 12:14:25 pm
content: Quote from: Wuerstchenhund on September 05, 2014, 09:12:49 amNot true: low Z 500? 10:1 probes are certainly capable of >1GHz. I was using them quarter of a century ago to see 750ps risetimes.Modern example from the HP/Agilent/Keysight heritage: N2874A Passive Probe, 10:1, 1.5 GHz, 500 ?, 1.7 pF, £285http://www.keysight.com/en/pd-1661742-pn-N2874A/passive-probe-101-15-ghz-13-m?nid=-34025.898996&cc=GB&lc=eng

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: September 05, 2014, 01:37:14 pm
content: Quote from: tggzzz on September 05, 2014, 12:14:25 pmYes, you can use a low Z passove probe at higher bandwidths. However, they are not really cheap, and only useful if you look at low impedance signals, and even then the active probes provide much better signal fidelity because of their much lower loading (capacitive and resistive, the input impedance of most active probes is in the 1GOhms range). It also helps a lot that the first signal amplifier sits in the shielded probe head (shorter from the signal).QuoteGood probe. Only that the 1.5GHz bandwidth will drop to 500MHz or lower when you try to use that probe with a dual lead adapter, which makes it a pretty poor choice for measuring most high bandwidth signals.You wrote that you were using similar 25 years ago, and maybe they were even adequate for what you needed them to do. But if you want to measure modern high bandwidth signals (i.e. modern buses like PCIe, SAS/SATA or such) then the active probe is the only way to go if you want to get accurate results that resemble the actual signal. Passive probes are pretty useless for that as they introduce huge errors.

author: David Hess
author_rank: Super Contributor
timestamp: September 05, 2014, 02:46:57 pm
content: Quote from: ethereal on September 05, 2014, 07:35:18 amI have several sets of Aidetek P6100s and they work fine up to 100 MHz.QuoteThere was a discussion thread on EEVBlog about these and they failed miserably. I thought they were a scam when I saw them and tests confirmed it.A general purpose high bandwidth probe is going to have several adjustments for transient response which are not necessary at 100 MHz and below. My Texas 250 MHz x10 probes have two transient response adjustments and work well on my Tektronix 300 MHz 2440 and 200 MHz 7A26s:http://www.ebay.com/itm/One-new-250MHZ-Oscilloscope-clip-probe-w-readout-pin-/280107318452There are 500 MHz versions of these probes available.If you plan on doing the transient response adjustment so the probes match your oscilloscope, then you will need a fast transition time reference flat top pulse generator of some sort. This is a handy thing to have for verifying proper function anyway.QuoteYou might want extra probes for things like oscilloscope external trigger inputs and timer/counters anyway. I use my cheap P6100s unless I need the higher frequency response of my Texas P5125s or want the x10 readout support for documentation purposes.If the P6100s had not been so inexpensive and I had not bought them first, I would have bought only Texas P5125s for even my 100 MHz oscilloscopes because I rarely need a x1 probe and having the readout correct is nice. The P6100s are great for frequency counters though.Quote from: Wuerstchenhund on September 05, 2014, 01:37:14 pmActive probes tend to have slightly worse transient response but this is seldom a problem. More serious may be their limited dynamic range, poor overload recovery time, and extra delay. None of these thing are insurmountable but the user should be aware of them.Quote from: Wuerstchenhund on September 05, 2014, 09:12:49 amI provisionally agree. Probe bandwidth assumes a 25 ohm source from a 50 ohm transmission line, 50 ohm termination, and coaxial connection which is usually unrealistic in practical applications. If the above conditions are met, then you can get full bandwidth out of a passive high impedance probe.QuoteI would be especially leery of used active probes since they are fragile and may be damaged in obscure ways. At the very least I would want a return policy and a way to test them myself to confirm that they work correctly.

author: nctnico
author_rank: Super Contributor
timestamp: September 05, 2014, 03:39:43 pm
content: I'm pretty fond of my Testec probes. They are not terribly expensive but not cheap either. As others notes: for high frequency signals you need a different kind of probe.

author: tggzzz
author_rank: Super Contributor
timestamp: September 05, 2014, 04:02:03 pm
content: Quote from: Wuerstchenhund on September 05, 2014, 01:37:14 pmAt those frequencies most signals have to be relatively low impedance, otherwise the stray capacitance in the circuit will have too much effect.QuoteIt is surprisingly easy to make your own low Z probe that is good to 1GHz; there are several web articles showing measured responses. They are very cheap in money, less cheap in time.QuoteI don't know what you mean by a "dual lead adapter", but bad techique will ruin the response ofanyprobe, passive or active!QuoteAlso greater than the current scope under consideration (1GHz va 500MHz).QuoteAgreed, but you aren't going to be looking at those signals on a 500MHz scope either.There's a good argument that for modern high speed "digital" signalsanyprobe will be problematic except at points which were explicitly designed to be probed.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: September 05, 2014, 04:48:58 pm
content: I really like Tek P6131's - small & light & very flexible cable.And the lumpy plugs are handy to coil up & hang the lead over when not in use.

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: September 05, 2014, 04:57:27 pm
content: Quote from: nctnico on September 05, 2014, 03:39:43 pm+1 for Testec

author: ethereal
author_rank: Contributor
timestamp: September 05, 2014, 11:35:36 pm
content: First off, thank you everyone for your opinions. I've been given some food for thought.Quote from: Wuerstchenhund on September 05, 2014, 09:12:49 amIt's aLeCroy 9354CTMscope. 500MHz, 500MSPS in quad-channel mode, 1GSPS in dual-channel mode, and with a PP092 adapter, 2GSPS in single-channel mode. Haven't invested in a PP092 yet, I'm waiting for a cheap one to come along. Also has 500Kpts memory per channel (which can be combined into 1Mpts in 2-channel mode or 2Mpts in 1-channel mode) and can make use of said memory pretty well. I talked it over with an EE friend, and he gave the scope his recommendation, given the price (about $300 USD, or roughly the price of a new Hantek/Rigol 'scope, but 500MHz and 4-channel). His opinion was that it should be perfectly fine for the work I'd like to do now, and should also provide some decent breathing room for future expansion.Quote from: David Hess on September 05, 2014, 02:46:57 pmThey seemed a bit unreal to me at the time, happy to see my suspicions confirmed! Thanks.QuoteI'll take a closer look at active probes. I was aware of them, but my internal model was indicating they were more useful at the 1GHz point and above, instead of ~500MHz. And if I grab some 100MHz/200MHz passive probes to start with, I can afford to be patient in the medium-term (couple of months). Since I'm planning to be using some LVDS as well, I'm also planning to acquire a differential probe, to save on a channel. That's more of a long-term goal, though.

author: tggzzz
author_rank: Super Contributor
timestamp: September 06, 2014, 12:08:57 am
content: Quote from: ethereal on September 05, 2014, 11:35:36 pmA "true" differential probe has the advantage of having fewer potentially "unequal" components between the signal and the subtractor.Will 500MHz be fast enough for your LVDS signals? There's a ruleof thumbthat the bandwidth should be 5 times the baud rate, in order to see the transitions. But so long as you are aware of your equipment's limitations, even a restricted bandwidth can be useful.

author: David Hess
author_rank: Super Contributor
timestamp: September 06, 2014, 12:13:59 am
content: Quote from: nctnico on September 05, 2014, 03:39:43 pmTestec is on my short list of probes to consider but availability has been a problem.

author: marshallh
author_rank: Unknown
timestamp: September 06, 2014, 12:39:16 am
content: I have four PP005/PP006 Lecroy 500mhz passive probes for my 9374C. Each cost about $70-90. That is a very good price, and you can probably find some on ebay still. Try to get complete ones (i.e. with all accessories)

author: David Hess
author_rank: Super Contributor
timestamp: September 06, 2014, 12:40:49 am
content: Quote from: ethereal on September 05, 2014, 11:35:36 pmI think you got a better deal than I did. I paid about that for a fully working Tektronix 2440 which is my "fast" DSO with a 300 MHz bandwidth, 500 MS/s for each of 2 channels under all conditions, and a 1k record length per channel. I do have full service documentation though.QuoteActive probes are definitely useful for more than high bandwidth. Like passive probes, their rated bandwidth assumes a 25 ohm source impedance but realistic applications will be higher so active probes will have higher bandwidth then passive probes at the upper range that passive probes will operate at because they have a higher input impedance.The high input impedance of active probes is also uniquely useful for differential measurements where unequal source impedances would lower common mode rejection.You can fabricate an active probe in the 100 to 200 MHz range pretty easily. I have occasionally designed active probe circuits into test boards which interface to the oscilloscope with just a 50 ohm cable.If your oscilloscope is sensitive enough, an alternative to an active probe and easier to build is a x100 low impedance passive probe. At higher frequencies, its input impedance of 5k can be competitive with an active probe.

author: ethereal
author_rank: Contributor
timestamp: September 06, 2014, 05:47:47 am
content: Quote from: tggzzz on September 06, 2014, 12:08:57 amI'm planning to work on circuits in the 30-100MHz range, so 500MHz of bandwidth should be just about right.Quote from: marshallh on September 06, 2014, 12:39:16 amWould you recommend the PP006 probes? There's someone on eBay selling them for $50 each, including what looks to be all accessories. Seems like a pretty good price from what I can tell...

author: nctnico
author_rank: Super Contributor
timestamp: September 06, 2014, 08:09:33 am
content: Quote from: David Hess on September 06, 2014, 12:13:59 amI buy them from Farnell / Element 14.

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: September 06, 2014, 10:05:14 am
content: Quote from: ethereal on September 05, 2014, 11:35:36 pmThat's a great scope at that price. In case you don't already know, you can get the software options for these scopes for free (you have get the necessary binary files to create the option GALs from the Yahoo LeCroy user group). Some of these options are only for niche areas (i.e. Disk Drive Measurements) but there are others (WP02, WP03 which gives you extended maths/FFT, JTA which is for Jitter Analysis, ATP which is advanced triggers etc) which are very useful in day to day work.

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: September 06, 2014, 10:13:56 am
content: Quote from: David Hess on September 05, 2014, 02:46:57 pmSure, they are somewhat fragile, but the same can be said about digital scopes or most other T&M kit that is regularly sold used, so there's really no difference here to buying other complex kit on ebay. Of course for everything that is reasonable expensive some warranty is a good idea (although even without seller warranty ebay is known to return money to the buyer very quickly if he's not satisfied with an item), unless the price is low enough to take a punt.Active probes like the LeCroy AP033 I bought can often be found in very good condition for less than $200 incl accessories.The beauty with the AP033 is that it is compatible with all LeCroy scopes from the old 9300 Series up to the current WaveRunner/WavePro scopes, so a change of scope doesn't mean having to replace the probe. They are also very rubust and reliable, and their only wek point is the upper part of the plastic probe grip housing which tends to break (and which requires a simple mechanical fix). Other than that there's not much that can go wrong with them.

author: tggzzz
author_rank: Super Contributor
timestamp: September 06, 2014, 10:58:22 pm
content: Quote from: Wuerstchenhund on September 05, 2014, 01:37:14 pmFor a6GHz passive probe, look no further than the hp/agilent/keysight 54006http://cp.literature.agilent.com/litweb/pdf/54006-90002.pdfThe manual discusses electrostatic damageto the attached scope, not the probe itself!Now I know that 6GHz is far from top-of-the-range, but I'd be interested to find an amateur that needed more!

author: Stray Electron
author_rank: Super Contributor
timestamp: September 08, 2014, 01:50:12 pm
content: Quote from: ethereal on September 05, 2014, 11:35:36 pmThat's a very GOOD scope IMO. I have a 9374CM and a 9370M. OEM probes for mine are the LeCroy PP005s and I think your's uses the same probes. I've had good luck picking up the PP005 probes on E-bay. I just got one for $25shippedand I bought three of them brand new for $160 in a package deal. I don't worry too much about buying from E-bay. As long as the seller lists the item asneworused, it MUST be fully working per E-bay's rules and if it's not then the seller must refund the buyer's money AND all shipping costs. I did get one PP005 probe that was intermittent and I told the seller about it and he sent me some other stuff that more than made up the price so I was happy with that deal.I strong prefer to use the OEM probes (unless they're junk) that way I KNOW everything with work as intended and I don't have to worry about capacitance mismatches or any of the rest.The Option GAL that the guy on E-bay is selling is well worth the money IMO! And that seller is VERY good about answering questions about LeCroy scopes. I HIGHLY recommend him! I also bought some SIMMS (E-bay) to max out the memory in my LeCroy and a PCMCIA memory card (E-bay again!).I bought my 9374CM for $75 in a surplus shop. I've paid about $210 for four NEW probes. $79 for the PCMCIA card, $28 (IIRC) for the Option GAL and about $30 for the two SIMMS so I've got a VERY nice 500 MHz, 4 Channel, LOADED, DSO for about $400.Oh and found like new, probably never used NEC floppy drive in a server in the same surplus store for $5. It was direct replacement for the bad one in the scope so now EVERYTHING is working in it!

author: ethereal
author_rank: Contributor
timestamp: September 20, 2014, 05:31:10 am
content: Apologies for resurrecting the thread, but I just came acrosstheseon eBay. Seems like an excellent deal to me with my limited knowledge set.I understand that they have a high impedance (2.2 MOhm), which will affect measurements at high frequencies due to the 12pF capacitance. Claimed rise-time is 700ps . . . but as an initial set of higher-bandwidth probes than the Chinese P6100s, they seems reasonable to me. (And yes, the oscilloscope that I now have (woo!) does have a 1-MOhm coupling option. EDIT: and the capacitance compensation range is similar to the probes that originally shipped with the scope.)Any thoughts?Thanks!- ethereal

author: David Hess
author_rank: Super Contributor
timestamp: September 22, 2014, 11:38:42 am
content: Quote from: ethereal on September 20, 2014, 05:31:10 amI wonder how they ended up with a 2.2 MOhm input.The probes should work but the high frequency transient response may be poor if they are not matched to the oscilloscope.