The need for a QRP output meter was felt when the homebrew SWR meters / RF ammeters in the shack proved useless for peaking the output of a homebrew 7MHz 5W solid state CW transmitter. For their pointers barely moved.
Hence the decision to build a RF milliammeter on the same lines as my
homebrew RF ammeter.
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| RF Milliammeter |
All parts were sourced from the junk box. BNC sockets were used. The primary of the toroidal transformer is a piece of the inner conductor of RG-58/U coax. The secondary is wound with a length of solid hookup wire. A rubber grommet ensures positioning of the toroid.
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| Inside the RF Milliammeter |
The small 1kΩ, 200μA FSD meter makes the unit quite compact. The enclosure of a defective 230V - 110V autotransformer came in handy, with the meter taking the place of the 110V socket.
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| RF Milliammeter - Schematic |
It was roughly calibrated to read around 250 RF milliamperes maximum. The CW transmitter was then easily adjusted.
Related post: Homebrew RF Ammeter
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