I would not in general expect fiberglass board to have high loss at 160M.
Regular non-UV rated fiberglass is a glass-reinforced polyester with
styrene.
HOWEVER... if this is some UV-rated fiberglass, it may have some more
exotic organic chemistry or some pigment filler that may have undesired
dielectric properties at RF. I'm not a chemist but I can't help but notice
that titanium dioxide (commonly used in light-colored UV protective
pigments) has strong dielectric properties:
http://en.wikipedia.org/wiki/Relative_permittivity
I have had very good success using polycarbonate for coil spacers etc. More
than its electrical properties, I love how easy it is to drill, bend, and
form.
Tim N3QE
On Sat, Jun 6, 2015 at 8:49 AM, Max Cotton <m0ghq@outlook.com> wrote:
> I have an inverted L antenna resonant on 80m, I decided to add a loading
> coil to the base to bring it on frequency for TopBand. I wound a 2.5mm wire
> coil 16 turns on a bit of square Paxoline board by drilling holes into the
> board each side and feeding the coil through the holes, a bit of a struggle
> but it worked, not very pretty, it is 146mm diameter and 120mm long 30.5uH.
> When I first tried it the SWR after small trimming was 1.2:1 band centre
> and 2.0:1 band edges. Now it looked a but ugly, so I decided to neat it up
> a bit by adding two fibreglass webs so the coil was now circular and held
> by a cross section instead of just the one plane, now when I retried the
> SWR it is still resonant on 1.800 but the SWR is now 2.0:1 in the middle of
> the band and 4.0:1 at the edges the turns are the same, the inductance is
> the same but I have lost my fine SWR curve. I only added the fibreglass and
> neated up the coil, Ideas what to do next apart from removing the
> fibreglass webs and goin
> g back to ugly coil?73 Max M0GHQ
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