[HomeBrew] 50 ohm receive splitter

[John Marshall]

Actually, the three-resistor splitter gives a 6dB reduction to each  
port.  You can draw the schematic and work out the voltage drops, but  
think about it - a perfect splitter would put half the power in each  
port for a drop of 3dB.  But if the power is passed through  
resistors, they have to dissipate some additional power so the drop  
has to be more than 3dB.

In the transformer-plus-resistor splitter, when the source and loads  
are properly matched, no power goes through the resistor, so each  
port is only down 3dB.  That's one advantage.  The second advantage  
is port-to-port isolation.  The three-resistor splitter will drop 6dB  
between any two ports regardless of which one is the nominal "input",  
so that is its port-to-port isolation.  An ideal transformer-plus- 
resistor splitter used with perfectly matched source and load  
impedances will have infinite loss (isolation) between the two output  
ports.  Non-ideal, real-world splitters used with matched source and  
loads can easily give 40dB or better isolation.  I've built and  
measured some with 40 plus dB peak isolation and better than 20dB  
over 1-30MHz.  OTOH, if isolation isn't an issue, the resistive  
divider is cheap and easy.

There's an excellent write-up on the transformer-plus-resistor  
splitter, also called "zero degree hybrid" or "magic-tee" at:
http://members.tripod.com/michaelgellis/magict.html

Here's an 8-port receiver multicoupler I built using these splitters:
http://www.babyloniangal.com/ku4af/RX_Multicoupler/
This may not be real helpful to anyone because I wound the  
transformers on small binocular cores from my junkbox, specs unknown.

John, KU4AF
Pittsboro, NC


On Dec 27, 2006, at 7:58 AM, ma.locksmith at juno.com wrote:

> ** Please do NOT cross-post messages when posting to HOMEBREW **
>
> The "good old" TV type splitter is only three resistors.....  each one
> third the impedance.....  for the 75 ohm circuit, they are 24 ohms.
> Result is a 3dB reduction in each port, and good to 900 MHz.
>
> What additional benefit is gained by using a transformer splitter?
>
> Ed
> K1ZOK
>
> On Tue, 26 Dec 2006 20:51:06 -0500 To Possibilities
> <topossibilities at verizon.net> writes:
>>
>> You can make a 50 ohm splitter by winding a bifilar winding on a
>> ferrite
>> core and adding a 100 ohm resistor.
>>
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