[TowerTalk] Snow and rain attenuation

[Jim Lux]

At 03:50 PM 10/31/2005, Jim Brown wrote:
>On Mon, 31 Oct 2005 16:32:50 -0800, Bob Nielsen wrote:
>
> >There are frequencies where there is a resonance with water molecules
> >which causes a quite high attenuation, even without rain or snow.
>
>My DirecTV receiver will die briefly during very heavy rain. I don't know
>what frequencies they're using,

about 12 GHz (Ku-Band)

>  but it isn't a very big dish, so there
>probably isn't a lot of gain margin.

probably around 5-10 dB. EIRP in orbit costs a bunch, so they figure pretty 
close to the edge.

>Remember -- it's a digital "cliff
>effect" -- that is, the signal fades gradually, but you don't notice it
>until the level drops so much that the system starts losing so many bits
>that it can no longer do error correction (or assemble enough bits to make
>a picture).

Jim W6RMK