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Re: Hybrid ring vs Wilkinson divider



----- Original Message -----
From: "Joop & Tineke Verdoes" <joop.verdoes@nameplanet.com>
To: "'AMSAT BB'" <amsat-bb@amsat.org>
Sent: Sunday, May 28, 2006 11:10 AM
Subject: [amsat-bb] Hybrid ring vs Wilkinson divider


> Fellow Amsat-ees
> While we now have some people on the list that are passionate about the
> subject of my question on power dividers I'd like to get a few opinions
> on what can be said about a
> "hybrid ring vs a wilkinson divider"
>
> Mechanically the wilkinson is just half of Domenico's hyrbid ring, legs
> 1-2, 2-3 are the same, but legs 3-4 and 4-1 are each replaced with a
> 50ohm resistor, so together with one 100ohm resitor. Outlet 4 isn't
> there anymore and neither the 50 terminator.
>
> While the interesting flurry of e-mail came in I looked up references on
> both and the key difference I understand seems to be that the
> - hybrid ring has a loss of 3db (input (2) vs sum of outputs (1&3))

Hi Joop, PA1JAV

The hybrid ring has not a loss of 3 dB
For example if you feed 50 watt to input (2) than 25 watt are splitted
to port (1) and 25 watt to port (3)
If you disconnect one antenna from port (1) or from port (3) than
25 watt cannot be radiated but they appears at port (4) where are
dissipated in the 50 ohm  termination and the SWR of the system
do not change.

                         3
                        /°\
                      /     \
                    /         \
                   /            \ 4       50 ohm
             2  °|              |°----/\/\/\/\----|
                   |              |
                   |              |
              1  °\            /
                      \        /
                        \    /
                          \/


The same is for a Wilkinson divider.
If both antennas connected at output port (1&3) are 50 ohm impedance
than the voltage across the 100 ohm resistor is 0 volt and no power is
dissipated in it.
For voltage across 100 ohm I mean the voltage as measured between
the resistor studs and not between the resistor and ground.
As soon you disconnect one antenna the voltage across the resistor
rises and half of the power is dissipated but the SWR do not change.

If you match two 50 ohm antennas to a 50 ohm transmission line
using 1/4 electrical wavelenght long of 75 ohm coax in series to
each antennas as usually we do in reality you have made a Wilkinson
divider in wich the 100 ohm resistor is omitted because we assume
that no antenna will be removed or damaged.
In this case as soon you remove one antenna the system is unmatched
and since the transmission line sees an impedance of 100 ohm instead
of 50 ohm if  the SWR before was 1 it will rise now to 100/50 = 2
and at best for several other reason.

> - wilkinson divider has NO loss (input (2) vs sum of outputs(1&3),
> obviosly each output leg gets just half of the input power)
> In each the leg(s) between 3 and 1 massages a possible unbalance and
> ensures isolation.

See the above discussion

>
> 73
> Joop, PA1JAV

Best 73" de

i8CVS Domenico
----
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