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Measuring Oscope Probe Bandwidth with an RF Sig Gen

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Berni:
Well the mention that it is a N connector usually points to big heavy RF synthesizers, the general purpose ones usually have BNCs and don't usually go that high in frequency.

For example the two Gigatronics RF synthesizers boatanchors (8 Ghz and 20 GHz) that i ended up with have a pretty long path inside. Behind the front panel N connector is a snaking rigid coax that takes twists and turns trough the instrument to end up at the switched attenuateor, then from there snakes around some more to end up at the directional coupler used for ALC, then snakes on some more to band switches and amplifiers...etc Most of these rigid coax lines taking some extra slack and bends in order to make them flexible enough to install without bending them out of shape. So you could quickly end up with half a meter of coax connecting the RF front end together, so lots of room for reflections to happen.

joeqsmith:

--- Quote from: joeqsmith on November 08, 2023, 01:48:04 pm ---
--- Quote from: David Hess on November 08, 2023, 09:58:49 am ---
--- Quote from: joeqsmith on November 08, 2023, 12:30:16 am ---
--- Quote from: David Hess on November 08, 2023, 12:22:54 am ---
--- Quote from: TimFox on November 07, 2023, 12:15:17 am ---The usual rule-of-thumb that RiseTime = 0.35/Bandwidth is not true in general for oscilloscope amplifiers, but is commonly used.
--- End quote ---

I have found it to be the rule rather than the exception, at least up to 300 MHz, but all of my oscilloscopes are old.

The oldest oscilloscopes that I know of where it is not the rule are some of the Tektronix 11k series plug-ins, and the 250 MHz option version of the 7704A.
--- End quote ---

Really old...
https://www.eevblog.com/forum/testgear/scope-speed-for-digital/msg3728101/#msg3728101
--- End quote ---

Mind are old, but the even older exceptions I mentioned above did not have Gaussian or first order responses despite being analog oscilloscopes, (1) and the DSOs that I have do have Gaussian responses so do obey the 0.35 rule, as do many modern DSOs which eschew the processing needed after digitization to produce a maximally flat response.

And then there are modern DSOs like the Rigol DS1000Z series which do not obey the 0.35 rule because their full power bandwidth is less than their small signal bandwidth, so their bandwidth varies with signal level.

(1) These old exceptions were tuned for maximally flat response like the DSOs discussed in the article, and suffered more aberrations in their pulse response, just like described in the article.

--- End quote ---

That 20+ year old article is about the age of my newest scopes.   


--- Quote ---Another commonly used property of Gaussian systems is the overall system bandwidth  .....   system bandwidth=1/(1/BWPROBE 2 +1/BWOSCILLOSCOPE 2 )0.5 . “System bandwidth” refers to the bandwidth you achieve with a combination of an oscilloscope probe and oscilloscope.

Oscilloscope probes are often designed to have sufficiently higher bandwidth than the oscilloscope bandwidth, so that the above formula is unnecessary for derating the system bandwidth. 
--- End quote ---

Most of my commercial probes are the limiting factor. 
https://www.eevblog.com/forum/testgear/12-ghz-active-probe-project/msg4988716/#msg4988716

I did construct a few resistive probes in that thread to demonstrate their performance.   My plan was to eventually measure their probes against some of my commercial ones.  Waiting on them to get a bit closer to a released product.     

Anyway, my only point was devil is in the details.

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My discussions with LeCroy and Tektronix
https://www.eevblog.com/forum/testgear/show-us-your-square-wave/msg593071/#msg593071

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