# I: DISH BEAM WIDTH

• Subject: I: [amsat-bb] DISH BEAM WIDTH
• From: "i8cvs" <domenico.i8cvs@xxxxxx>
• Date: Sun, 2 Mar 2003 02:12:35 +0100

```Oops..........
Hi Bill WA1DMV

I was wrong to type the gain of your dish wich assuming an
efficiency  of 50% is 36.5 dBi

Apologise

73" de i8CVS Domenico

----- Original Message -----
From: i8cvs <domenico.i8cvs@tin.it>
To: AMSAT-BB <amsat-bb@amsat.org>; <walnuthil@juno.com>
Sent: Saturday, March 01, 2003 5:29 PM
Subject: R: [amsat-bb] DISH BEAM WIDTH

> Hi Bill WA1DMV,
>
> A 12' dish (3.65 meters) in diameter at 2400 MHz has a -3 dB beamwidth of
> 2.2 degrees in the H plane and 2.5 degrees in the E plane
>
> The math is too long.
>
> Assuming an efficiency of 50% the gain is 31.5 dBi
>
> A simple but less accurate formula to calculate the -3dB beamwidth
> is to calculate the ratio lamda/D using the same units where lamda is the
> wavelengt and D is the diameter of the dish and than converting the result
> of this ratio from radians to degrees.
>
>
> lambda= 12.5 cm
> D= 365 cm
>
> 12,5/365= 0.0342 radians ; 0.0342 x 57.29= 1.96 degrees wich is very close
> to the above H and E plane angles to be calculate with a more complicated
> math bat for our amateur use the result is OK
>
> The F/D ratio is important only to designe the type and beamwidth of the
> feed to be used in order to illuminate the edge of the dish at -10 dB and
> this requires simple math that you can find in any antenna book.
>
> 73" de i8CVS Domenico
>
> ----- Original Message -----
> From: <walnuthil@juno.com>
> To: <AMSAT-BB@AMSAT.Org>
> Sent: Saturday, March 01, 2003 6:24 AM
> Subject: [amsat-bb] DISH BEAM WIDTH
>
>
> > Hello All,
> > I recently acquired a TVRO 12 foot dish, with the mesh
> > reflector. I have been trying to calculate the 3db beam width
> > in degrees, the books I have are not clear on the formula.
> > Does anyone have the correct math formula ?
> > Putting a 2 by across the dish and measuring down the
> > center is 22 inches. Yields a f/D = 4.0 if the formula is right.
> > I plan on using it for receive on AO-40, I have some tall pine
> > trees to the south that reduce the down link signal.
> > Hopefully this dish will help.
> > Bill
> > WA1DMV@amsat.org
> > #20942
> >
> > ----
> > Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
> > Not an AMSAT member? Join now to support the amateur satellite program!
> > To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org
>
>
>
>
>
>
>
>

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