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*Subject*: R: R: [amsat-bb] phase shift with coax*From*: "i8cvs" <domenico.i8cvs@xxxxxx>*Date*: Thu, 12 Jul 2001 21:28:13 +0200

----- Original Message ----- From: i8cvs <domenico.i8cvs@tin.it> To: Stan <stan@capeonramp.com> Sent: Thursday, July 12, 2001 4:47 AM Subject: R: R: [amsat-bb] phase shift with coax > > ----- Original Message ----- > From: Stan <stan@capeonramp.com> > To: i8cvs <domenico.i8cvs@tin.it> > Sent: Wednesday, July 11, 2001 9:32 PM > Subject: Re: R: [amsat-bb] phase shift with coax > > > > Hello Dom, > > > > The question of the day: > > > > if the far field boundary is at (2D**2)/lambda, > > > > is D the length of the boom for a single yagi antenna ? > > > > And is it four times for 4 identical yagis of a 2 x 2 array ? > > > > Most of my calculations have been for a dish where D is clearly > > the diameter. > > > > Stan, WA1ECF > > > > Hi Stan, > > The area of far-field begins at a distance R from the antenna greater than > (2D ^2) / lambda > where D is the diameter in meters of the antenna aperture or the antenna > capture area and so the far field boundary is directly proportional to the > antenna gain. > > In other words,greater the antenna gain,greater is D and greater is the > distance R from the antenna at wich the far field begins. > > In case of a parabolic dish D is the diameter of the dish,or the diameter of > his mouth in meters but in case of a yagi or any other type of antenna,D is > the diameter of his capture area A that can be computed using the following > formula. > A= (G x lambda ^2 )/ 4 x 3,14 [ square meters] > > We can assume that the antenna capture area A is a circle wich area in > square meters increases with the antenna gain G > > By geometry from the circle area A we can derive its radius > r= SQR ( A/3,14 ) [meters] > and so the diameter of the area is D=2 x r [meters] > > As an example we can use a 2 meters array made by 4 yagi in wich the gain > of a single yagi is 10 dBi > The gain of two yagi is than in theory 13 dBi and the gain for 4 yagi is > 16 dBi or 40 time in power over the isotropic antenna in theory. > > The capture area of this array is: > > A= ( 40 x 2 ^2 )/ 4 x 3,14 = 12,73 [square meters] > > from wich D= 4 meters > > If we call R the distance from the last director of the array at wich the > far field begins,than > > R= ( 2 x D^2 )/ lambda = (2 x 4^2 )/ 2 = 16 meters > > Conclusion: > > Greater the antenna gain and greater is the distance from the antenna at > wich the transiction from the near field and the far field begins. > > 73 de i8CVS Domenico > > > > > > > > Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA. > > > > To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org > > ---- Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA. To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org

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