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This is the follow up to:

UHF cubical quad VNA analysis interpretation

This is a S21 and S31 analysis of an oversized 385 Mhz 50 Ohm to 90 Ohm balun between 100 Mhz and 600 Mhz I tested phase separation and transmission loss for both ports.

If I interpret the results correctly, phase separation is pretty good over the 300 - 400 Mhz range. Transmission loss however is not good (more than 6dB loss, ideal should be 3dB loss) with one port more lossy than the other. I did not compute the common-mode rejection yet, I know there is a simple formula to calculate it from the VNA data. I did not test port isolation.

Now I will rethink the balun from scratch and scale it down. My questions are :

  • Do smaller 43 ferrite cores (10 mm OD, 7mm ID, height 3mm) will have acceptable performance at 400 Mhz ? (currently using 61 material 23 mm OD, 14 mm ID)

Also, port 1 ground and port 2 and 3 center tap are grounded to their respective PCB bottom layers. The PCB is split in two to prevent the grounds from contacting.

  • Is it acceptable practice to use a ground layer in baluns ? or should I discard grounds and connect grounded leads to their respective connector leads ?

For a detailed schematic, please refer to the previous post linked atop.

phase separation between port 2 and port 3

transmission loss in db for port 2 and port 3

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    $\begingroup$ Could you edit your question to make it a little more obvious what your specific question is? As it is, this reads like "here's an update on my project" at first glance. $\endgroup$
    – Kevin Reid AG6YO ♦
    Oct 8, 2019 at 15:14
  • $\begingroup$ This 'question' definitely does need something doing to it - otherwise it is going to get closed as "unclear what you're asking" $\endgroup$
    – Scott Earle ♦
    Oct 9, 2019 at 1:41
  • $\begingroup$ edited. indeed the questions were not highlighted. $\endgroup$
    – rodv92
    Oct 9, 2019 at 9:25

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