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 <[email protected]> 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 > _________________ > Topband Reflector Archives - http://www.contesting.com/_topband > _________________ Topband Reflector Archives - http://www.contesting.com/_topband
