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Hi Z versus 50 ohm impedance

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Aspiringloser:
Hello all!  Apologies if my first post has been previously answered in another thread.  I have a Siglent SDG 5082 function generator, Protek 6506 scope and a Siglent SHS 810 scope.  I've encountered an issue  that I don't understand.  With the function generator set to the 50 ? output, if I generate for example a 1 kHz sinewave at 1 Vp-p, both of my scopes measure 1 V peak, not peak to peak.  This is measured without being connected to any circuit, just the scope probes connected to the BNC to alligator clips on the output of the function generator.  When I switch the function generator to the Hi Z output setting, my scopes then measure the same peak to peak voltage which is being generated.  My instructor at school has touched on impedance matching with me in the past.  I took my scopes and generator to school to demonstrate my issue and he had no answer for me.  All of the function generators in the lab are older and my instructor isn't familiar with the newer stuff.  Does anyone have an explanation for this or a link to an explanation somewhere online?
Many thanks in advance,
Paul N. Wise.

c4757p:

--- Quote from: Aspiringloser on April 15, 2014, 01:01:11 am ---I took my scopes and generator to school to demonstrate my issue and he had no answer for me.

--- End quote ---

That's just sad.

The function generator has a 50 ohm output impedance internally - this never goes away. When it drives a 50 ohm load, the two form a voltage divider that cuts the signal in half. Therefore, if you tell it there's a 50 ohm load at the other end of the cable, it will compensate for that by doubling the signal amplitude. That's all.

T3sl4co1l:
FYI...

What voltage do you get from the function generator?

If you answered "what it says", YOU'RE FLAT WRONG!

That's just what it's programmed to generate.  It's not measuring what it's actually putting out.  It's *certainly* not measuring what's at the end of the cable!

Always measure with the scope, in circuit!  That way you know for sure.

Tim

uprightsquire:
Recent video by w2aew: http://youtu.be/tClE8s6RZdg

FrankenPC:

--- Quote from: uprightsquire on April 15, 2014, 01:08:51 am ---Recent video by w2aew: http://youtu.be/tClE8s6RZdg

--- End quote ---

One of the  best beginners video I've seen.  The other best beginners video was his db discussion.  The man is awesome.

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