2
$\begingroup$

I own an Ed Fong TBJ-1 antenna, which is like a twin-lead J-Pole with a coax stub and some inductors added. It's enclosed in an unfinished PVC pipe.

I'm tempted to paint the PVC with non-conductive UV inhibitors, but don't know if that will de-tune the antenna. What effect does something like Krylon paint / UV resistant clear coat have on a tuned antenna that's enclosed by PVC pipe?

$\endgroup$
  • 3
    $\begingroup$ This is just an educated guess, but the PVC pipe likely affects the antenna much more than the paint would. $\endgroup$ – Mike Waters Aug 22 '17 at 22:16
  • $\begingroup$ You're correct, according to the patent (US9608336 B1): "As the velocity factor associated with the PVC pipe affects the antenna performance, the detuning effects of the PVC pipe are taken into account when fabricating the antenna, individually and in mass production quantities." But will painting an antenna tuned for PVC cause additional problems? $\endgroup$ – user3486184 Aug 22 '17 at 22:29
  • 2
    $\begingroup$ Compare thickness of paint with thickness of PVC pipe. assume similar material properties. So, no. (don't use conductive paint, but I guess that one's obvious) $\endgroup$ – Marcus Müller Aug 22 '17 at 22:45
  • 2
    $\begingroup$ I doubt it, and that's what I was trying to say. I think that it will take some time for the PVC to deteriorate to the point where it gives you a problem. To set your mind at ease, you might Google the permittivity (dielectric constant) of what you propose to use as a coating vs. PVC. (Having said that: If I were you, I would not hesitate to spray it on.) $\endgroup$ – Mike Waters Aug 22 '17 at 22:45
  • 1
    $\begingroup$ @MikeWaters spoke, and thus, I did. $\endgroup$ – Marcus Müller Aug 22 '17 at 22:54
5
$\begingroup$

No.

Even if the electromagnetic material properties of the paint were drastically different than that of air, the few microns of coating won't be even measurable. (Unless that coating really is conductive paint)

Another thing: You've bought an antenna. Building exact antennas is hard. If you worry about the effect of 30 µm of paint coat, then you'd also have to worry about the effect of temperature, shrinking and expanding the PVC pipe. Or the fact that no one cuts conductors for antennas with a 30 µm accuracy.

Why are you worrying? It's not like your antenna was exact to a high degree anyway. In fact, measurement antennas whose directivity is known to less than a percent are expensive. Price of a small car for antenna expensive. With a dipole variant antenna like yours, you'd be happy if the actual center frequency (ie. the point of highest matching to the nominal impedance) everything is let's say with +- 10% of what you expect. It won't work worse if a slight wind blows, but that would flex the PVC much more than a coating would add.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.