Friday, June 19, 2020

High Power - RF Power Divider (Splitter)

MATH!!! - bet you never thought Math would be something useful in life did you?

I decided to try to build based on this:

But I soon found it pretty difficult to locate metric metal in the USA.  So I decided to use the calculations provided in the URL but to substitute with slightly larger common sizes found in the USA at your local hardware store.

Here is what I came up with based on their design:

  • Impedance of the quarter wave transformer
    • Z1 = Coaxial cable impedance = 50 Ohm
    • Z2 = Antenna's combined Impedance = 2 ports = 50 / 2 = 25 Ohm
    • = 35.355 Ohm
  • Impedance of a square tube with round center tube
    • Now calculate the impedance, Zo, of a square tube with round center tube
      • D = ID (inside dimension) of the square tube = 1.25" (inches)
      • d = OD (outside diameter) of the round center tube = 0.75" (inches)
      • This equates to an error of 0.36% from the ideal to the practical which is excellent
  • The length of the transformer is a free space quarter wave of 50.313 Mhz
    • Length = 300 / (50.313 * 4) = 1491mm (from N-type pin to pin) = 58.70 " (inches)
      • See NOTE1 below

So this comes out to:
  • Square tube dimensions 61.25" x 1.5" OD (1.25" ID) (PAY ATTENTION! critical)
  • The Copper tube is 3/4" OD (Outer Diameter - PAY ATTENTION! critical)
  • From Connector Input to Output N-Type center to center pin is: 59 1/4"
    • NOTE1: This is a deviation from the "Length of the transformer" note above.  I can't explain why/how I came up with this length because it doesn't match the calculated values above.  But this IS what I've used.
  • From END to center pin at Input is: 1"
  • From END to center pin at Output is: 1 3/8"

In the following photo I'm just resting the tube on the pins.  Before Soldering them.

Below - before soldering

Below - after soldering

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