Topband: Fwd: Dielectric effect on bare vs. coated wire

[Herb Schoenbohm]

Thanks Frank and Uli, Today I was able to remove the insulation of the 
quad driven element wire(s) and test the results. Zounds! Amazing change 
as everything came back to normal. The Three element Cubex Quad is now 
broadbanded ( as when I first installed it with #14 bare before i made 
the mistake of restringing it with #16 covered solid) with the 1:1 
bottom at 14.150 rather than at the lower band edge. You guys were spot 
on with you observation. It is strange that I have never in all these 
years seen any reference to this quad building although I have seen this 
effect mentioned with 160 meter BOG radials. Now I guess I will wait for 
a long boom bucket truck as stripping the insulation of the outside 
elements would normally require taking this monster down. I have thought 
of every possible way to do this by not having the expense of taking 
everything down and/or a boom truck with a 80 foot reach and spinning 
the outer elements as the tower climber (my son) spins the boom and I 
strip the wire. My neighbor even suggested using a propane torch on the 
end of a pole but that doesn't seem reasonable. Shortening the wires was 
not an option because they are all strung on pre-set holes in the 
fiberglass. Perhaps a 3% long reflector loop and director loop might not 
cause a pattern reversal, which appear to be the case from all the 
preliminary tests. But i still eventually want to get things correct. 
73, Herb, KV4FZ

  On 7/26/2013 8:13 PM, donovanf at starpower.net wrote: > Hi Herb, > > 
Dielectric loading causes insulated wire to have a lower velocity factor 
than bare wire. > The velocity factor of your particular wire can be 
determined experimentally. > > This is exactly the same as the 
dielectric loading that occurs when ice covers > our quads and Yagis (I 
sure you're forgotten about that in the Virgin Islands!) . > Ice 
increases the VSWR and in extreme cases reverses the directivity of a 
Yagi. > This is exactly the same as what you're experiencing with 
insulated wire. > > All of the loops (reflectors, driven elements, 
directors) in your quad are now resonant > at a significantly lower 
frequency than intended. As far as I know, the only was to > solve your 
problem is to shorten all of the wires or replace them with bare wires. 
73 Frank W3LPL