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grafityy , 04-30-2025, 05:32 PM

Hello,

I try to measure mine (1/10 150MHz passive probe) using my LiteVNA, between 10kHz and 1GHz (I have calibrated my LiteVNA for this freq. range). But there are things that puzzle me :

- Why do I get some S21 > -20db at some frequencies.... ? My probe is a passive 1/10 probe, so normally I cannot have any voltage output signal for any freq > 0.1*input_signal because 0.1 is -20db and my probe is passive ... no ??
- Why S21 is not -20db near DC but minus infinite db ? Normally, as my probe is a passive 1/10, I should get -20db at DC no ??? If I send a DC voltage at input, I should receive a DC -20db voltage at output and not a 0Vdc voltage ....
- S11 is not an infinite negative value, normally no signal is returned at DC no ??

It seems S21 and S11 are inversed at DC...

Any idea ??? Thanks you !!

grafityy , 04-30-2025, 05:58 PM

grafityy , 04-30-2025, 06:04 PM

And also, in the "Stimulus" menu, there is an option I don't know how to configure : CW FREQ... perhaps it's because I have not set it correctly ? And also the CENTER Freq ??

QDrives , 04-30-2025, 08:37 PM

Passive probes (usually) are not lossless. This allows you to use them with 1M ohm impedance scope inputs.

grafityy , 05-01-2025, 07:51 AM

Ah ok thanks 👍