Hi Guy,
Good topic.
> The losses as a reversible beverage would far exceed those used as a
> balanced feedline, because of the balance partly cancelling fields in the
> dielectric between them.
Slow wave structures are more common in microwave. Anything that increases
capacitance or inductance per unit foot will slow wave propagation. The
formulas are 1/f*sqrt LC for wavelength, and 1/sqrt LC for phase velocity.
I built short Beverages with multiple ferrite sleeves, because a thick
dielectric was impossible. There are limitations for how slow we can make
the wave that change with antenna length, after which the antenna reverses.
This is why most slinky Beverage "theory" put out was nonsense, because the
real action isn't packing a wave of wire in a small area....but rather
slowing the velocity factor a correct amount. I *think* the limit for a half
wave structure is a Vp of about .5 before the system reverses and starts
firing backwards, but it has been years since I looked at slow wave
structures for 160.
Velocity factor in this case is caused by the interaction of dielectric and
electric field, specifically the increase in capacitance. The electric field
is actually more concentrated between the two wires when voltages are
out-of-phase, so the dielectric has more effect.
When in parallel mode, more of the field is outside the line dielectric in
air, although the field is more intense near the conductor.
By the way, this is one of the "rubs" in making a Beverage really long.
> Is there really anyone actually using this stuff for reversible beverages
> on 160??? This stuff could make you plumb deaf on 160.
I would avoid things that slow the wave in longer antennas. Phase is already
bad enough in long low wires. A very thick dielectric certainly would not
help as an antenna becomes longer. As it becomes longer, the arriving wave
would be increasingly out-of-phase with current in the wire. But the primary
velocity factor and loss effects are going to be in differential mode, where
the field is most concentrated between conductors.
73 Tom
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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