Fractenna wrote:

. Of course mesh parabolas

typically only have 80% of the gain of a solid dish,

I would seriously doubt the veracity of this statement and would be
gratified to see valid documented evidence of this. If the mesh openings
are under 0.1 lambda the mesh will appear solid. The problem may be
achieving good surface accuracy with a mesh dish.Those of us using mesh
dishes on 1296 MHz EME are seeing excellent efficiencies with mesh surfaces-
ultimately limited by the ability to properly illuminate the surface. For
EME we tend to underilluminate the surface to take advantage of lower side
lobes and less spill over, which means "seeing" less warm earth noise.

Dale W4OP


Hi Dale,

A wok has no focal 'point': it is not a true paraboloid. Its the imperfection
in shape, not mesh:-) Ergo the loss in aperture efficiency.

For the purposes of radio signals, does the shape need to be a specific
paraboloid? Certainly at optical wavelengths a parabola is needed to
focus light from infinity, so a parabola is needed. But at radio
Frequency wavelengths a true parabola is not likely needed. In fact,
considering the difference between a sphere and a parabols, I would
suspect that anything out there is not a true parabola unless it is
arrived at by chance.

- Mike KB3EIA -