# Re: todays math problem

• Subject: Re: [amsat-bb] todays math problem
• From: K5OE@xxxxxxx
• Date: Tue, 04 Feb 2003 03:29:41 -0500

```Bob,
One of the biggest factors in dish gain is the efficiency of illumination, but ignoring that complexity (since you didn't give us any specifics) and assuming a 50% efficient dish/feed combination in both cases, a convenient short-cut equation for "typical" dishes at 2.4 GHz is:
Gain = Log10(0.256 * Area in sq in.)

Thus:  791 sq in = 23 dBi and 1959 sq in = 27 dBi

...for a delta of only 4 dB.  Roughly, each doubling of the dish aperture is worth 3 dB when all other variables are unchanged.

73,
Jerry, K5OE/G

In a message dated 2/3/2003 9:49:50 PM Eastern Standard Time, w7lrd@juno.com writes:

> Hello
> Bob has two dishes, dish 1 is 1959 square inches. Dish 2 is 791 square
> inches.  So dish 1 is about 2.5 times larger than dish 2.  Bob thinks
> dish 1 should be 7.5 db better than dish 2, that's 2.5X3db,
> or maybe a
> little over one S unit. Is Bob right?
>
> 73...Bob...W7LRD
> Seattle
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