Simple VHF SWR Protection Circuit [VHF Bridge Directional Coupler - SWR Protection] Here is a simple SWR protection circuit you can easily build.

Simple VHF SWR Protection Circuit

Here is a simple SWR protection circuit you can easily build. The directional coupler and detector components are from an old VHF SWR meter.You may want to replace the meter's existing RF bypass Capacitors with higher quality (mica) ones.

You may also want to replace the line coupler's termination Resistors which higher wattage ones. Be sure to use the exact same value, or the SWR meter will be inaccurate. Also, be sure to use non-inductive Resistors (carbon-film or metal-oxide will work).

This then feeds to all LM3914 bargraph display to light the LEDs, indicating the current SWR ratio. SWR When the ratio reaches approximately 3, it will engage the relay, cutting off the RF input to the power amplifier . You could also just a LED light or sound an alarm if you want to.

You should compare the circuit schematic above to this one below :

Visit this links for more, 4W FM Transmitter Directional Coupler with RF Filter for 88-108 MHz - 100w LCD PIC16F88 SWR Meter for VHF- UHF and click this link for building: The Windows ® program for drawing analog meter scales.