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I primarily use a Baofeng for most of my contacts. I've got a pretty good antenna (14.5 inch whip), but when I have to pack it into any sort of bag, I'm always worried that it'll get bent. This has happened to me with another antenna.

I figured I could 3D print a case for it, but now I'm wondering: If I were to keep the 3D printed case on the antenna during operation, would it interfere with the antenna itself?

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  • $\begingroup$ What's the dielectric constant of the material you're using? Does it get hot in a microwave oven? $\endgroup$
    – Mike Waters
    Feb 5, 2023 at 21:31

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Sure, material within the near field of an antenna effects the match, the efficiency, the directivity and phase center of the antenna (so, everything that describes the antenna), but:

Assuming "3D print" means ABS, PTFE, PLA or any of the other popular polymer materials and not something conductive or highly specialized, at the near-DC frequencies of commercial ham radio handsets, this will not play a role at all. (especially considering how long wavelength is and how much higher-$\varepsilon_r$ materials are in the vicinity, like, but not limited to, hands, heads,…)

So, print away, and use during operation. At these powers and frequencies, a few hydrocarbons around your antenna don't matter at all.

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Even insulators have a dielectric constant, so putting a case over an antenna, especially a UHF/VHF antenna, can detune it. How much this matters depends on the base bandwidth of the antenna. If you detune it out of its bandwidth, it won't work, but if it has a wide bandwidth to start with, it may not matter. (Some of the lowest dielectric constant materials are glass and fiberglas, which is why fiberglas is frequently used to enclose antennas.)

For example, ladder line J-pole antennas have a notoriously narrow bandwidth (which can be fixed by increasing the diameter of the radiating section), and putting them in a PVC pipe for structural integrity can detune them badly. However, you can take this into account and cut the j-pole a slightly different length to compensate and it will work fine.

On the other hand, don't put your antenna in a carbon fiber raydome. Carbon fiber makes a great faraday cage. (I suppose if properly shaped and fed, it would also make a great antenna.)

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    $\begingroup$ Yes! A thick case could definitely affect an antenna. Just note that most Plastic has Er≈2.3, 3D-printed will contain some air so maybe closer to 2.0. Fibreglass Er≈4.3 $\endgroup$
    – tomnexus
    Feb 7, 2023 at 18:12

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