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*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. > > 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

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