Optimizing a low frequency Wilkinson power combiner

Discussion in 'General Technical Questions and Answers' started by 2E0ILY, Jul 3, 2019.

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  1. 2E0ILY

    2E0ILY Ham Member QRZ Page

    Thanks to kind forum members I now have the information needed to build a Wilkinson combiner for use combining 2 or 3 LF Class D amps running at 137 kHz.

    I now have a few questions re possibly optimizing them. If I use an on line calculator to wind an air cored inductor of 81.85uH on a former of outside diameter 75 mm it tells me to wind 55 turns. But if I measure using an in calibration Fluke LCR meter that excites at 1kHz, it shows 82uH. From past experience using an AIM4170 antenna analyzer set to excite at the operating frequency of 137.5kHz I will get another reading again.

    The on line calculator for a 3 port combiner is here: https://leleivre.com/rf_wilkinson.html

    So, to my questions. Do I attempt to wind the inductors with their design impedance measured at 1kHz according to the Fluke LCR, or according to 137kHz injected via y AIM4170 antenna analyzer?

    Or once wound can I optimize in real time like this? Inject a sine wave of 0dBm at 137.5 kHz into one output port, put my SA on the other outlet port, and a 50 Ohm load on the input jack. Then add / remove turns looking for the minimum level on the SA port?

    I presumably need top do this in combination with looking for minimum insertion loss when injecting the signal into the input jack, and getting the least loss at each output port, with the other output port terminated in 50 Ohms?

    Or do I just wind according to the various air cored inductor calculators and not worry about how good or bad it is if it seems to work OK , which it does?

    But how much better it could be is nagging a bit.... Thanks!

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