This is a little experiment at building a circuit that seems easy, but may not actually be that simple.  I needed 0° power splitter for my 10 MHz precision frequency standard project.  I picked up a Minicircuits ZFSC-2-1 on eBay which solved my immediate need, but the allure of experimentation is too strong to resist!

The purpose of a splitter (also called a divider, combiner or splitter/combiner) is to send two or more copies of a signal to multiple devices (or vice versa).  A 0° splitter keeps both copies in phase, while 90°, 180° and others do not.  There is a ton of information online that delves deeper into the subject, but two particularly good ones are's "RF combiner, splitter / divider basics" and Minicircuits' "Understanding Power Splitters".  Wikipedia's "Power dividers and directional couplers" article is a great resource too.

My project required the output signals to be in phase with each other since it's a precision timing application and the Minicircuits device covers that well.  So I thought it would be fun depart from the phase requirement and do some tinkering.

This is a simple transformer with the input connected to the primary, each leg of the secondary going to one of two outputs and a center tap on the secondary going to ground through a 27Ω resistor.

The real fun here was machining a Minicircuits-style housing for it.  To accommodate BNC connectors, I used 2" x 2" 6061 aluminum square tubing for the body and made nesting end plates from 2" x 1/4" flat bar.  By milling a recess around the edges of the end plates, a tight RF seal is formed.

RF Splitter Components
RF Splitter Components (click for a large view)

For a first try, I used a T44-7 core with 14 turns on the primary and 21 turns on the secondary.  It's no good.  I need a core with higher permeability, so that will be coming in a future post.

Anyway, here's what it looks like assembled:

Splitter Guts
Splitter Guts
(click for a large view)
Splitter Assembled
(click for a large view)

In the near future, we'll try an FT37-61 core and see what difference that makes.  I also think that building it onto some copper clad PC material could make a better ground plane for impedance control, but first, the transformer itself needs to be improved.

Here's the electrical proof that it sucks compared to the Minicircuits device.

Minicircuits ZFSC-2-1
Minicircuits (click for a full view)


Homebrew (click for a full view)

Learning is fun!  More to come later . . .

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