[time-nuts] Antenna question about RHCP/LHCP I'm sure a time-nutcan answer

Attila Kinali attila at kinali.ch
Tue Jun 5 10:47:55 UTC 2012


On Mon, 04 Jun 2012 23:11:14 -0700
Jim Lux <jimlux at earthlink.net> wrote:

> On 6/4/12 10:44 PM, Chris Albertson wrote:
> > On Mon, Jun 4, 2012 at 10:18 PM, Hal Murray<hmurray at megapathdsl.net>  wrote:
> >>
> >> What is the significance of the pointy tops of the long skinny antennas?
> >>
> >
> > Guessing.   Terminates the end of the conductor to prevent a discontinuity
> > and reflection

Or maybe better adaption to free space impedance....

> 
> more likely it's for structural reasons. A lot of helical antennas are a 
> wire or tape on a cruciform cross section core (rather than on a tube). 
> You don't want that corner sticking out.
> On the tube, it's easier to make a cone end, then a flat pillbox, and 
> you don't have the diaphragm vibration mode on the flat end.

Do you mean that the end of the cruciform helix does vibrate and that a
cone that ties the end at the center is free of that vibration?

> >
> > How about the collars at the base of them?
> >>
> >
> > Another guess: They kill multi path reflections from supporting structure
> 
> or provide a better match. Or both..

According to a paper on GPS i've read recently, it's to better control
the side and back lobes of the signal. The graphs showed quite some
improvement of the radiation pattern. If anyone is interested, i can
look up the name of the paper.


			Attila Kinali

-- 
It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
                 -- Miss Matheson, The Diamond Age, Neil Stephenson



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