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*Subject*: RE: [amsat-bb] Dish questions for 2.4GHz and 24GHz*From*: "Tom Clark" <tac@xxxxxxxxx>*Date*: Thu, 20 Sep 2001 22:44:26 -0400*In-Reply-To*: <000201c14242$19990ce0$b2472fd8@abraxis.com>

> -----Original Message----- > From: owner-AMSAT-BB@AMSAT.Org [mailto:owner-AMSAT-BB@AMSAT.Org]On > Behalf Of Don Woodward > Sent: Thu, Sep 20, 2001 22:03 > To: amsat-bb > Subject: [amsat-bb] Dish questions for 2.4GHz and 24GHz > > > Would the dish below from DH Satellite be suitable for 2.4GHz now and then > be adaptable to 24GHz later provided substitution of two correct > feed mounts > and feeds? > > Don Woodward > KD4APP > They don't say anything about the quality of the dish surface. To have good efficiency, a dish should have an RMS surface accuracy (both the general shape of the parabola, and the roughness of the surface) "smooth" at levels of 1/20 wavelength. Since 24 GHz = 1.3 cm, this means that the quality needs to be at the 600 micron level. And a 1.2 m dish operating at 1.3 cm has 120/13 = 92 wavelengths in its aperture. Therefore the beamwidth (full width at half max) will be ~1/92 radians (the fact that the aperture is circular actually ~1.22/92 = .013 radians = .76 degrees = 45 arc minutes. To use such a dish you will need to somehow point it to a fraction of the size of the beam, i.e. something in the range of tens of arc minutes. Just to put this in perspective, the hour hand of an ordinary 12 hour analog clock moves thru 360/12 = 30 degrees per hour. at 24 GHz, you would have to be able to point this dish to an accuracy better than the angle that the hour hand moves in a minute of time in two dimensions. So the dish might work at 24 GHz, but I'm not sure that you would find it very useful! 73 de Tom, W3IWI ---- Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA. To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org

**Follow-Ups**:**Re: Dish questions for 2.4GHz and 24GHz***From:*John Stephensen, KD6OZH

**References**:**Dish questions for 2.4GHz and 24GHz***From:*Don Woodward

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