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50 ohm inputs for Siglent SDS1104X-E

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Veteran68:

--- Quote from: the_cake_is_a_lie on December 31, 2023, 11:36:46 pm ---Is there any advantage of using those adapters over a BNC T adapter with one end fitted with a 50 ohm terminator? That's what I have and the combination is slightly cheaper. Maybe the adapters are more convenient and that's enough justification.

--- End quote ---

It's not the same, but depending on what you're measuring, it may or may not make a critical difference. If you're not into sophisticated high frequency RF, the T-adapter terminator is probably good enough.

Here's a link to a recent video of Joe's where he's comparing different through terminators and mentions the drawbacks of the T-adapter termination. Relevant content is at 3:55 into the video.

https://youtu.be/gy10caH95Qg?si=o80vL_-NN5GuyMo-&t=235

Njk:

--- Quote from: Roger Need on December 31, 2023, 06:07:41 pm ---I bought several of these P57 adapters to use with my Siglent 1202X-E.

--- End quote ---
I've three. To be known, a maintenance on arrival was needed for all of them, to make them actually usable. The round cup was hard to rotate but easy to get it stuck. A considerable force was necessary to overcome the friction, causing excessive wear to the metal parts. This is not how a good BNC connector supposed to work. A tiny drop of gear oil in proper place solved the problem. Perhaps the boxes of more expensive brands are lubricated at the factory while in this case it's left to users. Not a big deal though

the_cake_is_a_lie:
Cool thanks. My interpretation is under 50 MHz that I'm interested in, it doesn't matter. At some high enough frequency, the termination method makes a difference and being hardcore and wanting PFC on a probe or scope's parasitic capacitance, maybe you got to DIY. If we say 1 GHz has a 30cm wavelength, a 3cm or so extension on the T splitter is enough to generate reflections and we might wonder how close to 50 ohms the resistor really is.

joeqsmith:

--- Quote from: the_cake_is_a_lie on January 02, 2024, 12:50:48 am ---Cool thanks. My interpretation is under 50 MHz that I'm interested in, it doesn't matter. At some high enough frequency, the termination method makes a difference and being hardcore and wanting PFC on a probe or scope's parasitic capacitance, maybe you got to DIY. If we say 1 GHz has a 30cm wavelength, a 3cm or so extension on the T splitter is enough to generate reflections and we might wonder how close to 50 ohms the resistor really is.

--- End quote ---

I would say that's basically going to be true. 

Personally for high speed designs, I most likely am using specialized probes and scopes.   The thru terminations mentioned would never come into play. 

While I never came right out and stated it, that video with the SPICE simulations was more just to show why the original Pasternak thru terminator that used axial resistors out performed my original ones made with surface mount parts, once we considered the effects of the scopes loading.   I assumed most picked up on that when I was presenting the data.   Maybe not..

alm:

--- Quote from: the_cake_is_a_lie on January 02, 2024, 12:50:48 am ---Cool thanks. My interpretation is under 50 MHz that I'm interested in, it doesn't matter.

--- End quote ---
Just be careful that this is 50 MHz bandwidth, not a 50 MHz repetition rate. If you are looking at the rising edge of a fast 50 MHz square wave, that may well require much more bandwidth than 50 MHz and hence be much more sensitive to termination.

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