Swr protection for 160m linear amplifier

Discussion in 'Wireless & RF Design' started by mosfet80, May 24, 2010.

  1. mosfet80

    Thread Starter New Member

    May 24, 2010
    Hello. I have a mosfet's linear amplifier for 160m and i am looking for swr protection.
    Do you have any idea/circuit to add at output to protect my linear? Thank you very much.
  2. bertus


    Apr 5, 2008

    You could make a SWR meter and look at the reflected power.
    If that becomes to large you could reduce or even cut the power to the end stage.

    Attached is an example of an SWR meter.

  3. skeptic

    Active Member

    Mar 7, 2010
    Typically a directional coupler is used to detect the reflected power. The reflected power is detected and used to lower the output power of the transmitter.

    Directional couplers often are 1/4 wavelength for the frequency of interest. If they are less than that, higher frequencies will couple better than the lower ones. A quarter wave coupler may be difficult to do at 160 meters.

    They work by running the coupled line for approximately 1/4 wavelength along the antenna line. The distance between the two lines is chosen so that the capacitive coupling equals the inductive coupling. Inductive coupling produces a directional current in the coupled line but capacitive coupling flows in both directions. This means the inductive and capacitive coupling cancel in one direction and add in the other. Sometimes directional couplers have trimmer capacitors to adjust the capacitive coupling so that you get a good cancellation.

    You may be able to construct one by using an RF transformer for that frequency and appropriate capacitors.