At 10:52 AM 2005-03-25, Clive Whelan wrote:
>NO!, using PVC coated wire. I thought it was implicit in the W4RNL data that
>wire issues all cancelled out. Is that not the case do you think?
Clive,
The presence of PVC or other thick plastic insulation can lower the
resonance by a few percent.
The latest version of EZNEC (4.0) has a provision to include wire
insulation in the "Wires" description. I modelled 0.05 inch thick PVC on a
20 foot high dipole made of #12 wire at 21.2 MHz. For resonance with the
insulation, the dipole was 21.66 feet long. Without insulation, it had to
be 22.64 feet long (4.5% longer). Looked at the other way, if you designed
for 21.2 MHz with (implied) bare wire, using PVC insulated wire would lower
resonance to 20.28 MHz.
I'm not sure how thick your insulation is, but this could explain some of
your issues.
The other consideration with Moxon rectangles is what you do with the wire
at the ends. It might be important what type of insulators (glass,
plastic, etc.) and how you wrap the ends of the wire onto them. A little
added capacitance between the ends of the two elements could warp the
performance somewhat.
Good luck!
Terry
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