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Switch-out SWR Bridge

For QRP work, a resistive (lossy -6dB) type that you switch out of circuit after use is the best. However I don't think these are made commercially! You sometimes see this simple circuit with QRP rigs and I suggest you get a local to build it, possibly a novice!

The circuit uses a double pole changeover switch (Measure or Operate), a SWR C/O switch Forward & Reverse, three 50 ohm resistors rated at 1/4 RF power, one RF diode (OA81), two 1nF capacitors, a series meter calibration variable resistor (10K) and a meter (100uA).

It is best to make it from an old CB meter as you get the Box, Meter SWR scale, sockets and switches. Sensitivity is down to about 0.2V of RF at the detector which is about 0.8mW. Depending on the layout and components used, the meter could be accurate to VHF.

73 De John, G8MNY @ GB7CIP

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