Products > Test Equipment
Inexpenive 50 Ohm Feed Through Terminations
graybeard:
In this video I review why you need to use a feed through termination and show an example.
Then I do review of a low-cost (2 for $10) feed-through termination and compare it to ones from Tektronix and HP including measurements with a network analyzer.
The results are interesting and not what you might expect. The low-cost ones and expensive name brand ones all perform the same when connected to an oscilloscope input.
Chris
n3mmr:
You connect the f-t termination to the scope input and then connect the attenuator to the termination?
I e source->cable->attenuator->f-t_termination->scope_input?
TimFox:
That is correct. When the 50-ohm terminator is on the attenuator output, the impedance looking into the other end of the attenuator will be 50 ohms.
RoGeorge:
Thank you for showing the Smith chart for when the terminator is also directly connected to an oscilloscope input. :-+
David Hess:
Most modern oscilloscopes only have one high impedance attenuator stage (1) which explains the difference between 100mV/div and 200mV/div and why there are basically only two sets of curves.
Is it possible that at 100mV/div and lower, the signal level from the VNA is triggering the oscilloscope's shunt input protection? If there was really that big a difference, it should show up as a change in probe compensation between 100mV/div and 200mV/div and if that happens, the oscilloscope is broken.
I have two of the 5 watt Tektronix feedthrough terminations that you mention. Actually one was sold by Probe Master and is marked as such so either Probe Master or someone else was OEMing them. They are lower performance than the smaller Tektronix feedthrough terminations but up to 300 MHz, perform just as well.
(1) This also means that they operate their high impedance input buffer over a much larger signal range which is detrimental to performance. Older oscilloscopes with 3 or even more high impedance input attenuators perform better.
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