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50 ohm inputs for Siglent SDS1104X-E
joeqsmith:
--- Quote from: alm on January 02, 2024, 08:51:10 am ---Just be careful ...
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True.
I suspect Rodger's 30dB @ 700MHz return loss was without the terminators attached to their scope. This is what graybeard had suggested I measure way back when. Just took me a few years to get around to it. The video I made walked through the basic math and simulation to show why this is and how it could potentially be improved.
https://www.eevblog.com/forum/testgear/50-ohm-inputs-for-siglent-sds1104x-e/msg5252313/#msg5252313
MathWizard:
So SMD resistors don't have much parasitic capacitance, but is it mainly that, which screws up the P57 response past 800MHz or less ?
David Hess:
--- Quote from: skander36 on December 31, 2023, 09:04:16 am ---On a Micsig scope (TO 3004) I have obtained even a slightly a better rise time with this load resistor(P57) than with it's internal 50 ohm path.
The result was 1,060 ns for internal 50 ohm and 0,993 ns with P57. With another source the result was 1.606 ns external 50 ohm(P57) and 1,879 ns for internal 50 ohm.
--- End quote ---
I would assume that the difference is caused by peaking because of inductance in the resistor or layout.
--- 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.
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There will be a difference at higher frequencies, but likely no difference at 50 or 100 MHz.
--- Quote from: Njk on January 01, 2024, 09:31:26 pm ---
--- 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.
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I've three.
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I have collected two different types over the years. I always wanted one of the small Tektronix ones as a standard for performance, but ended up with a pair of the larger 5 watt Tektronix ones which are only good to a lower frequency, and one of the 1 GHz ones like that discussed here.
joeqsmith:
--- Quote from: MathWizard on January 02, 2024, 11:24:32 pm ---So SMD resistors don't have much parasitic capacitance, but is it mainly that, which screws up the P57 response past 800MHz or less ?
--- End quote ---
If you followed along in that video where I went over some of the basic math and simulate the termination, I am suggesting it is the scopes input that screws up the response, which I assume is why graybeard asked my to look at it.
the Chris:
--- Quote from: joeqsmith on January 03, 2024, 05:08:29 am ---If you followed along in that video where I went over some of the basic math and simulate the termination, I am suggesting it is the scopes input that screws up the response, which I assume is why graybeard asked my to look at it.
--- End quote ---
I enjoyed watching the video a lot, great presentation of measurements and their evaluation.
My takeaway was that for best performance, a custom termination is adjusted to the individual scope on which the termination is going to be used. I especially liked the use of an inductance to linearize the response. Felt like adusting a speaker crossover.
Thanks for the recording,
Christian
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