Fw: [amsat-bb] Power divider for X-yagis (amended)

["i8cvs" <domenico.i8cvs@xxxxxx>]

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
----
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