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*Subject*: R: [amsat-bb] DISH BEAM WIDTH*From*: "i8cvs" <domenico.i8cvs@xxxxxx>*Date*: Sat, 1 Mar 2003 17:29:00 +0100

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. In your case: 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. > Thanks in advance > 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 ---- 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

**References**:**DISH BEAM WIDTH***From:*walnuthil

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