Dish size rating document ?

[brentb636]

I've been poking around trying to find an authoritative document on dish size. What makes a 31 inch dish , a " 31 inch dish " ! Is it the effective aperture of the offset dish that defines it's size rating ? Curious because I'd like to be able to estimate the "dish size rating" of various elliptical dishes ( compared to oval offset dishes ) .
I realize that there is a certain amount of leeway ( nominal values being what our language is made up of), but if anyone can steer me in the storm, I'd appreciate the attention. Currently I'm working off the vertical demension as being a ballpark figure for nominal dish size.

Thanks,
Brent

 

[linuxman]

Hi Brent,

That is an excellent question. I have asked the same question on another forum, and gotten various answers.

The most obvious answer was one from Mike Kohl who raised the point that the two common Primestar dishes have numbers associated with them like the 84e and the 75e which if you accept the numbers at face value, you have an 84e = 33" rated dish, and the 75e = 30" rated dish.

In my opinion both of those dishes perform better than their rating.

I too would be very interested in just how the process works, the numbers behind the process, and the formula for arriving at the rating. Diagrams and pictures would be great too.

Fred

 

[GrumpyGuy]

This issue started bugging me when I started shopping for my first dish.

Apples to apples comparisons would be much easier if manufactures sold their dishes by the effective square inch of reflector (or square centimeter, or circular mil, etc.)

 

[brentb636]

No wonder you're so grumpy !

 

[Anole]

(LNB) size matters, too

I think for the elliptical dishes, you can't expect full signal into your stock LNB
The usual "round" horned LNBs look at a round dish.
For those obviously wide dishes, you need a proper feedhorn on the LNB.

...or is this a significant problem...?

Does it only matter if you are illuminating the dish for transmisson?
Does it only matter if you are trying to ignore ground noise or other local interference?
(is that a problem on Ku band?)
It probably only matters if the LNB can't see all the way to the edge of the elliptical dish.
(is seeing beyond the top and bottom a problem?)

Can someone try a good Invacom with a round feed horn on their elliptical dish, then replace it with one mated to the proper feedhorn, and report the difference?
That would sure make me feel better. :