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*Subject*: Fw: [amsat-bb] Power divider for X-yagis (amended)*From*: "i8cvs" <domenico.i8cvs@xxxxxx>*Date*: Sat, 27 May 2006 12:23:24 +0200

Hoops ! I was wrong typing........sorry ! The characteristic impedance of coax cable to be used for Section 1-2 Section 2-3 and Section 3-4 of the following hibrid ring for 145 MHz must be 75 ohm and not 50 ohm. The following text is correct. 73" de i8CVS Domenico > > Hi Peter, N4IP > > I agree completely with you and infact for my 2 meters X yagi I have used > for several years a very simple and effective hibrid ring made of coax > cable as per the following drawing. > > > 3 > /°\ > / \ > / \ > / \ 4 50 ohm > 2 °| |°----/\/\/\/\----| > | | > | | > 1 °\ / > \ / > \ / > \/ > > For 145 MHz and using coax cable with velocity factor 0.66 > > Section 1-2 , Section 2-3 and Section 3-4 are each long 1/4 electrical > wavelenght made with 34 cm of 75 ohm coax cable RG 11 or RG 59 > depending on TX power. > > Section 1-4 is a single run long 3/4 electrical wavelenght made with > 1024 cm of 75 ohm coax cable RG 11 or RG 59 depending on TX > power > > The impedance at port 2 is 50 ohm and if a 50 ohm feedline is connected > to a TX/RX than the power appearing at ports 1 and 3 is divided by two > (3.01 dB) and both signals appearing in 1 and 3 are in phase. > > The impedances at port 1 and 3 are 50 ohm and both ports are in phase so > that each dipole of the X yagi must be connected to 1 and 3 using two runs > of 50 ohm coax cable having the same lenght and taking in account if a > delay line is used or not to get circular polarization. > > Port 1 and port 3 are isolated between them by at least 30 dB so that one > dipole cannot see the other and the circularity do not suffer too much in > case of small difference in SWR between them but in case of fault of a > dipole the 50 ohm termination must be capable to dissipate 1/2 of the > full TX power. > > This hibrid ring can be built on a brass plate with 8 holes having the > same diameter of the braid of the coax cable used for it. > > The 8 braids of the coax sections and the 3 flanges of the N connectors > must be tin soldered to the brass plate. > > To save room all sections of coax cables can be shaped in any form and the > full job using material available in any junk box take about half day. > > About the problems that arises when the antenna is not purely resistive > in our discussion we should consider the complex impedance R+jX and > R-jX of the antenna and not only a simple 50 ohm impedance but this > refinement was not requested by the PA1JAV question. > > Best 73" de > > i8CVS Domenico ---- 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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