Yes, 1206 is rather large. ?I¡¯ve not opened up the 478A or the other thermistor sensor I have for use with the 432A, one goes to 10GHz and the other to 18 GHz, but I would check into smaller resistors. ?0805, 0603, 0402, 0201, and the near-microscopic 01005 are common. ?I think they even go smaller than 01005. ?Conventional wisdom says smaller ones have lower parasitics. ?Good luck. ?HTH.
Jim Ford
Laguna Hills, California, USA?
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On May 19, 2025, at 3:19?PM, jmr via groups.io <jmrhzu@...> wrote:
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Sorry, I made a typo the graph title should say inductance in nanohenries (nH) not uH. The measured Ls for the 1206 capacitor is 1 nH.
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Here's a simulation for the VSWR if the thermistors are not tracking perfectly. This is the case for when one thermistor is 90R and the other is 110R.
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Whilst this still looks really good, the VSWR rapidly degrades to 1.04:1 at 50 MHz if the thermistor tracking degrades to 80R + 120R. I've not show this case as it is probably unlikely to happen unless the sensor has been stressed at some point.
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<H75 VSWR Model_trackingerror.gif>
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Regards
Jeremy
