|[AMRadio] antenna tuners|
k4kyv at hotmail.com
Fri Apr 21 19:14:58 EDT 2006
>From: "Gary Schafer" <garyschafer at comcast.net>
> > Another factor causing loss with a high SWR is dielectric losses at the
> > recurring high rf voltage points along the line. At low impedances, it
> > the resistive loss in the wire, and at high impedances, it is dielectric
> > losses that combine to cause signal loss. But SWR is much, much less
> > critical than most hams have been led to believe.
>It is my understanding that at HF only resistive loss comes into play.
>Dielectric loss isn't a problem until you get into vhf.
I would say it depends on what kind of balanced line you use. If it is well
insulated, real open wire line, with ceramic or low-loss plastic spreaders,
there is probably negligible dielectric loss at hf or even lower vhf. But
if it is solid dielectric feedline, or even that pseudo-open wire line stuff
that is basically heavy duty TV lead-in with square holes punched in the
dielectric, I suspect there would be dielectric losses even at hf, and that
they would increase with substantial SWR.
The same goes for solid dielectric or foam type coax.
However, for moderate SWR's, the loss is much less serious than most hams
have been led to believe.
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