IN3LBQ on the Hühnerspiel (Amthorspitze) - photo by IN3OTD

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:

20 dB coupler schematic

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:

coupler test fixture

And here is the board after mouting the two toroids, ready for the first measurements:

20 dB coupler

note that each line has one of the traces gap shorted out with a small piece of wire.