Can I surround the antenna with tinted plastic

In article ,
Tony James wrote:

Can I surround the antenna with tinted plastic

Tony-

The effect depends on frequency. On 4 MHz, you may not notice any
difference. On 400 MHz, you may need to adjust length of antenna
elements.

Fred

In article ,
says...

Can I surround the antenna with tinted plastic

Tony-

The effect depends on frequency. On 4 MHz, you may not notice any
difference. On 400 MHz, you may need to adjust length of antenna
elements.



It will also depend on the material of the tint. It should be
nonconductive.

On Sun, 5 Jul 2020 02:06:54 -0700 (PDT), Tony James
wrote:

Can I surround the antenna with tinted plastic

I try to ignore one-line questions. They usually don't include enough
information to properly answer the question. What's missing a
1. What are you trying to accomplish? Numbers and specifics are
helpful.
2. What do you have to work with? That includes your abilities,
experience, test equipment, availability of parts, etc.
3. What have you done so far and what happened? Where are you stuck?

Take a small sample of the tinted plastic and put it in a microwave
oven. Cook it for maybe 15 seconds. If it's warm, it's absorbing RF
and probably unsuitable for covering an antenna (radome).

"Tinted Plastic" is not a very good technical description. It would
be helpful if you would provide the type of plastic. You can then
lookup the loss tangent or dissipation factor to determine if the
plastic will work as a radome.
http://www.g3ynh.info/zdocs/comps/part_6.html

Some materials will detune your antenna. At VHF, UHF, and above, that
will have a substantial effect on performance, even if the radome
material does not absorb any RF. Look for tables of velocity factors
or dielectric constants.
https://members.tm.net/lapointe/Plastics.htm

Tinting is a separate problem. Even if the plastic is fairly RF
transparent, the dye or additive used could absorb some RF. The only
way to know for sure is to test a sample of the "tinted plastic".

Mo
https://www.researchgate.net/post/What_are_RF_transparent_materials_you_know

Good luck.
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Sun, 05 Jul 2020 10:18:00 -0700, Jeff Liebermann wrote:

Take a small sample of the tinted plastic and put it in a microwave
oven. Cook it for maybe 15 seconds. If it's warm, it's absorbing RF
and probably unsuitable for covering an antenna (radome).

You should always do this with a companion glass of water.
Microwave ovens do not like running without something "in the box"
to act as a dummy load in to which to dump the power.

Jonesy
--
Marvin L Jones | Marvin | W3DHJ.net | linux
38.238N 104.547W | @ jonz.net | Jonesy | FreeBSD
* Killfiling google & XXXXbanter.com: jonz.net/ng.htm

On 6 Jul 2020 17:50:43 GMT, Allodoxaphobia
wrote:

On Sun, 05 Jul 2020 10:18:00 -0700, Jeff Liebermann wrote:

Take a small sample of the tinted plastic and put it in a microwave
oven. Cook it for maybe 15 seconds. If it's warm, it's absorbing RF
and probably unsuitable for covering an antenna (radome).

You should always do this with a companion glass of water.
Microwave ovens do not like running without something "in the box"
to act as a dummy load in to which to dump the power.

Jonesy

Agreed. It's safer to give it something to cook or boil. However, I
don't think it's necessary for this test. 15 seconds of cooking
plastic isn't going to kill the magnetron from over heating due to
reflected power or over voltage due reinforcement of voltage peaks.
Also, see:
https://physics.stackexchange.com/questions/309154/what-happens-in-an-empty-microwave-oven
All the microwave ovens I have ever come across,
dismantled or repaired have always included a "stirrer"
which is in the waveguide path between the magnetron
and the oven cavity. Usually it is in the form of a
metal rotating shape like a fan. This chops up the
otherwise nicely formed e-m microwaves into a jumble
and hence there can be virtually no standing waves
inside the oven.

"Microwave stirrer for microwave oven"
https://patents.google.com/patent/US4833286A/en

I guess I should mention that this test should be performed in a
microwave oven that is not used for cooking food. Plasticizers,
VoC's, fireproofing, UV proofing, nasal desensitizers, dyes, paint,
clear coatings, and other noxious volatiles are not considered edible.
Please remember that you have only one life to give to your hobby.

Also, for antennas that can be crammed into a tubular radome (also
known as a plastic or fiberglass pipe), a VNA is quite handy to view
the detuning effects of the plastic radome. The VNA produces a
frequency sweep across the operating range on the X axis, and a
corresponding VSWR or return loss on the Y axis. For example, on VHF:
"nanoVNA-H – standalone VHF antenna VSWR sweep"
https://owenduffy.net/blog/?p=16052
It's really discouraging watching my calculations turn to trash as the
antenna resonant frequency moves when a radome is placed over the
antenna.



--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558