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Recently I built a helical resonator. It took me a good while to adjust it since I had to trim my coils much shorter than calculated. The calculation said 7.2 turns but it ended up being more like 6.5 turns. The coil was built on a custom 3D printed form (PETG material), so it's very close to ideal.

Could the difference in inductance be attributed to losses in the plastic form? If so, is it possible to estimate the decrease in self resonant frequency due to the form's dielectric constant, to allow for quicker tuning?

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  • \$\begingroup\$ Yes the DK of plastic ~2.2 will reduce fo \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Feb 22 at 20:07
  • \$\begingroup\$ @TonyStewartSunnyskyguyEE75 is it possible to calculate by how much? or are measurements always required in this case? \$\endgroup\$ – hjf Feb 22 at 20:43
  • \$\begingroup\$ Proximity and thickness of plastic and air gap affects everything which is why VHF helix tends to be non plastic with large air gaps between turns \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Feb 22 at 21:02

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