[amsat-bb] 13 cms Antennae

[John <g3bvu@xxxxxxxx>]

	HB9DRV de G3BVU   

At 10:23 8/17/05 +0200, you wrote: 
>What are the 13 cms polarisation considerations? 
> 
>I am looking at these three dishes: 
>http://www.kuhne-electronic.de/id-elektronik/index.htm 
> 
>Simon Brown 
>--- 
	+++++++++++++++++++++++++++++++++++++++++++++++++++++++ 
	Simon, 

	The two "Kuhne" antennae (I do not see a third) you show are not true 
dish antennae. Being a GRID style, with metal rods in only one plane, 
they will reflect only waves that are polarized in that plane. In the 
case shown in the pictures it is HORIZONTAL polarisation. A vertical 
polarized wave will pass through the grid and not be reflected into the 
FEED. 

	The listing claims both antennae will also operate in a vertical 
polarisation mode. This is true ONLY IF YOU ROTATE THE ANTENNA ASSEMBLY 
90 DEGREES so that the rods (and FEED) are vertical. In this case 
horizontal polarised waves will pass through the grid; only vertical 
polarised waves will be reflected into the feed. 

	One other geneal point: 
	With a "solid" dish, whether it is a solid piece of metal or a solid 
sheet with small holes in it, signals of all polarisations will be 
reflected into the feed. However the FEED must support both horizontal 
and vertical polarisations for the complete dish/feed assembly to 
respond to both polarisations. Note in your pictures the FEED appears to
be a dipole, with reflector and that that the dipole and the rods are 
both in the same plane. If the dipole only was rotated 90 degrees, the 
antenna assembly would (ideally) receive NO SIGNALS! 

	73s,  de G3BVU   SK 
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