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Author Topic: Wilkinson combiner coil induction measurement question  (Read 2196 times)

2E0ILY

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Wilkinson combiner coil induction measurement question
« on: March 21, 2017, 03:39:33 AM »

If I plug my desired frequency (137.55kHz yes, kHz, I am inputting 0.13755MHz) into this on line calculator I get a figure for the two coils of 81.82uH each

http://leleivre.com/rf_wilkinson.html

I have two coils prepped with a few excess turns, and can measure with a calibrated Philips LCR meter at 1kHz, or I can try and measure them with an AIM4170 antenna analyzer at 137khz. Is it important to measure and trim them at 137khz or not please? Can I assume the on line calculator is assuming measurement at the operating frequency? Am I likely to see much difference? Thanks.
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Best regards, Chris Wilson.

G3RZP

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RE: Wilkinson combiner coil induction measurement question
« Reply #1 on: March 21, 2017, 06:56:07 AM »

Measuring at the operating frequency will take into account the self capacity of the coils, which affects the apparent inductance.
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2E0ILY

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RE: Wilkinson combiner coil induction measurement question
« Reply #2 on: March 21, 2017, 07:00:26 AM »

Thank you Peter, that is what I shall attempt to do then, may I just ask if I set the AIM4170 analyzer up as for a 50 Ohm load when I do a bespoke calibration?
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Best regards, Chris Wilson.

G3RZP

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RE: Wilkinson combiner coil induction measurement question
« Reply #3 on: March 21, 2017, 04:05:59 PM »

Presumably. I would measure with a Q meter or a calibrated capacitor and a FET probe and  a 'scope or Valve Voltmeter. Any analyser that relies on measuring return loss has a problem with measuring with any real accuracy impedances (or reactances) far away from 50 ohms. For example, the difference in return loss between 2500 ohms and 2400 ohms  is around 0.1 dB. Which is why, although these modern analysers are quick and easy to use, I still prefer my old GR and Wayne Kerr RF bridges.
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