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20 dB HF coupler
Under construction...
Another classic design, a 20 dB directional coupler using two transformers in a configuration popularized by the Tandem Match wattmeter in QST and several editions of the ARRL Handbook.
Its schematic, with the ports numbering used for the following graphs, is shown below:
I quickly prepared a small PCB to hold the few components needed, cutting out the traces from a double-sided board with a rotary tool. The end results didn't look too bad - even the traces impedance was later measured to be quite close to 50 Ω!
Here is the coupler fixture prepared with SMA connectors:
And here is the board after mouting the two toroids, ready for the first measurements:
note that each line has one of the traces gap shorted out with a small piece of wire.