Transmission Line Reflections VE3KL

Select Transmitter Type

Transmitter Power [Watts]    
Load SWR
Source SWR
Line Loss [dB]
This calculator is used to evaluate the performance of transmission systems. The block diagram of the system is shown in the figure below. The transmitter is a source of power. It can be a real radio transmitter, a signal generator or a receiving antenna that sends power to a receiver. The lossy transmission line connects the transmitter to a load which can be any passive load such as an antenna, filter or receiver. The analysis was carried out using signal flow graphs. Please note that the link above is a large file of approximately 1 Mb.

 Forward Power [Watts]
 Incident Power at Load [Watts]
 Power Delivered to Load [Watts]
 Power Reflected From Load [Watts]
 Power Reflected at Source [Watts]
 Power Lost in Transmission Line [Watts]

To use this calculator:
  • First Select the Transmitter type.
  • Then input the parameters in the input boxes. Boxes that are Yellow indicate that these values are selected by the program and not by the user.

    Insert numbers from 1 to 1000 for the transmitter power.
    Insert numbers from 0 to 30 for the line loss.
    Insert numbers from 1 to 100 for SWR values.

  • Press the Calculate button to see the results.
There are three transmitter types that can be selected:
  • The first type is a simple conjugate match where the characteristic impedance of the transmissionn line equals both the load and source impedance. In this case there are no reflections at either end of the transmisson line. The line is lossy in general and the calculator computes power deliverd to the load. A conjugate matched system can be used to simulate a receiving antenna or a small signal signal generator that has an output impedance of 50 Ohms.
  • The second type is a linear system where neither the SWR at the load or at the source is matched. Simply, input the desired data that describes your system.
  • This calculator is for a special case where reflections add in phase. In more compex situations, the power delivered to the the load can be worse.

  • The third type is used for solid state transmitters where all of the power that is reflected back to the source is again reflected. Hence the SWR for the source is infinite. The calculator uses 1000 for the source SWR to simulate this effect.