© WB5CXC 2011
Antenna Matching Calculations
You can use a 1/4 wave length matching stub to match your transmission line to your load.  Some antennas are designed with a different impedance than 50 ohms.  Using a 1/4 wave length matching stub you can transform the transmitter coax into another impedance.  An example is you have a full wave 20M loop which is 100 ohms.  Using the calculation form below. In the Top Section you enter in 50 ohm and 100 ohm and it gives an answer of 71 ohm matching stub. In the Middle Section you enter in the frequency of 14.2, select RG-59 (right side - 75 om coax), and it tells you will need a length of 103.5 inches. 
Top Section The Top Section you will enter the transmitter Coax impedance, Antenna impedance, an it will calculate the impedance of the 1/4 wavelength matching stub.     Middle Section The Middle Section you enter the frequency of your system, select the type of coax, and it will calculate the length of coax needed for a 1/4 wavelength matching stub.  Bottom Section The Bottom Section you enter the transmitter coax impedance, select the type of matching stub (difference types of coax & number in parallel), and it will calculate the end impedance of the matching stub. 
Using the Calculation Form
_ Transmitter Coax   RG - 174 50 ohm RG - 58 50 ohm RG - 8X 50 ohm RG - 8X 50 ohm CQ Mini RG - 11, RG - 59B/U 75 ohm RG - 62A/U 93 ohm RG - 83/U 35 ohm RG - 8 50 ohm    
  Antenna Impedance    
  Matching Coax Impedance    
  Frequency   Mhz    
  Velocity Factor    
  1/4 λ Coax   Inches    
  (length of shield)  
      50 ohm coax 75 ohm coax 93 ohm coax 2 - 50 ohm coax 2 - 75 ohm coax 3 - 93 ohm coax    
  Find Impedance with Matching Stub  
  Transmitter Coax    
  Stub Impedance    
  Impedance to Match