# Terminating a 50 Ohm source into 1M Ohm oscilloscope input

Due to buying some equipment several months apart I am now faced with the task of connecting a high speed ,up to 1GHz, light detector that requires a 50$\Omega$ load impedance, but my oscilloscope only offers a 1M$\Omega$ input impedance.

Can I connect via a tee piece and a 50$\Omega$ terminator? Are there other options to connect the detector to the oscilloscope?

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That sounds like the simplest method and usually does the job. What is the part number of the detector? –  Andy aka Mar 3 '14 at 15:08
I've seen in-line 50 ohm terminators - they'd be less likely to introduce discontinuities than a Tee. –  Peter Bennett Mar 3 '14 at 17:42

If you don't have access to a $50 \Omega$ feedthrough terminator, a T-connector with a $50 \Omega$ termination should work just as well. This was standard practice at my old company when we used external hall-effect current probes with our $1 M\Omega$ scopes.

(Aside: I personally prefer using external $50 \Omega$ terminators even if the scope supports $50 \Omega$: they're usually capable of handling more power, and if you accidentally hook up something incorrectly, at least you're blowing an inexpensive and easily-replaceable component vs. necessitating a potentially expensive scope repair!)

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This may work for you but you might see some distortion at higher frequencies because of the termination not being at the end of the cable. Think of the other connection to the oscilloscope as a stub of unterminated line which will create nulls in the measured signal depending on the length.

They make feedthrough terminators for this purpose.

Feedthrough Terminator

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