Scope Probe...What the difference between 100MHz and 500Mhz? - Page 1
Forum section: electronics / general

author: riscy00
author_rank: Contributor
timestamp: February 26, 2014, 05:12:20 am
content: I wish to establish reason why scope probe has 100Mhz, 300MHz, 500MHz spec for very similar price. Is there key difference internally within scope problem?. They could sell just 500MHz and do away with lower frequency.http://www.ebay.co.uk/itm/1PC-150-200-250-300-350-400-Or-500-MHz-Oscillo-Scope-Clip-Probe-Kit-X10-X1-600V-/221309549262?pt=UK_BOI_Electrical_Components_Supplies_ET&var=&hash=item338713baceCan anyone recommend cheap 500MHz scope (un-named) for 500Mhz scope and what is your experience with them?

author: nctnico
author_rank: Super Contributor
timestamp: February 26, 2014, 09:53:22 am
content: Look at the circuit you want to probe first. 99.9% of the high frequency circuits won't like being probed with a load of 10pf. My rule of thumb is that you need a low capacitance (<1pf) passive divider RF probe or active FET probe for probing signals over 100MHz. 500Mhz looks good on a high impedance probe but it's practical usage is very limited due to the capacitance at the tip.

author: riscy00
author_rank: Contributor
timestamp: February 26, 2014, 03:10:43 pm
content: Thank for input but Active probe is not scope of the discussion. I familiar with them.I'm more interested in general what internal difference that qualify 100Mhz and 500Mhz scope probe even for cheap china crap or Tek/Aglient/Lecroy branded. I do not see much reduction in probe cap between 100Mhz and 500Mhz which lead me to this question.....what market 500Mhz they sell even it input cap would screw up measurement.I have google search and found no obvious answer.

author: KJDS
author_rank: Super Contributor
timestamp: February 26, 2014, 03:30:44 pm
content: http://cp.literature.agilent.com/litweb/pdf/5990-8576EN.pdf

author: saturation
author_rank: Super Contributor
timestamp: February 26, 2014, 05:21:08 pm
content: I sincerely doubt those probes linked on eBay can do anything more than 200 MHz. For 3 reasons.First, the technique and technology to make passive probes to 500 MHz hasn't changed since Tektronix wrote the book on it in 1969. See link for Tek Probe Circuits by Weber and other links, the chapters on passive probes is still valid.https://www.eevblog.com/forum/suggestions/scope-probes-teardown-and-diff-probe-investigation/Second, thus, all probes ~> 300MHz often havefixedattenuation [10x or 100x] and2 compensationadjustments. Pictured on those photos there is only one BNC adjustment and they are still adjustable x1, x10 even up to 500 MHz.Third, every probe has a voltage limit per frequency; you need to consult the curve but in general all the passive has a similar curve, its usually down to >20Vp at ~> 200MHz. This probe makes it appear its applicable at 600Vp without qualification.Even cheapo no-name but hard to find China 500 MHz passive probes are about $80-100, delivered.I'd recommend you get the Pico Scope clone TA049, which is a rebadged Chinese 'Texas' 500 MHz probe. These are both copies of the 1970s circa Tek probes. The Pico scope version is at least checked for QA and performance by Pico versus the unknown from the Texas variety. I own this and know it works.http://accessories.picotech.com/passive-oscilloscope-probes.htmlhttp://www.ebay.com/itm/ezprobe-TEX500RA-Texas-TX6150-x10-500MHz-NEW-/151240238924?pt=LH_DefaultDomain_0&hash=item23369ee74cA newer design made for B&K scopes run $100 in the US, can be found cloned too, but not cheap$100-200, PR500B. I would suggest buy the B&K brand if you choose this model as its carried by most legitimate US distributors and is warranted by B&K. I do not know this design while the Pico design is more established and thus easily hack able if needed.http://www.digikey.com/catalog/en/partgroup/pr500b-probe/33654Quote from: riscy00 on February 26, 2014, 03:10:43 pm