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I have a NanoVNA-H4,

I have no problems checking antenna SWR etc.

But what I want to do now is to check the performance of a "Diplexor"
You know one of these things that splits/combines a 2 meter and 440 antenna into one common output.

You know one of these.

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I want to measure the insertion losses for each band.? and then the amount of isolation between the bands.

Can anyone show me a video on how to do this? OR give me a step by step on how to do it?

Joe WB9SBD

Hi Joe

You seems need an S21 Logmag measurement , Knowing that dynamic range of H4 on the UHF are limited to 50db you should not expect more then -45db values for the isolation measurements between the Two bands, obviously you need a 401 sweep points , and many complete 401 point calibrations for each bands (with isolation and Throught) , each calibration should be focused on the desired slice of the band under test, you need to reset the old calibration for each new calibration to be sure to avoid interpolation errors ,
Good Luck.
73's Nizar

To measure insertion loss, you connect the channel 1 to the common port of the diplexor and channel 2 to one of the output ports while terminating the unused port with a 50 Ohm load. Move channel 2 to the other output port and terminate the remaining output port with 50 Ohms.
To measure isolation you connect channel 1 to one of the output ports and channel 2 to the other while termination the common port in 50 Ohms. Switch the connections on the output ports to measure the other isolation.
Gary
W9TD