MATH!!! - bet you never thought Math would be something useful in life did you?
I decided to try to build based on this: https://www.gare.co.uk/6m_antenna/divider.htm
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
- 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