[[!img notes/Characterising_a_coupler/IMG_20180930_203828.jpg size=300x300]]
+The directivity doesn't match the datasheet, even at low frequencies, but I
+might blame the 50R termination...
+
+<table>
+<tr>
+<td> [[!img notes/Characterising_a_coupler/IMG_20180930_203828.jpg size=300x300]] </td>
+<td> [[!img notes/Characterising_a_coupler/IMG_20180930_203828.jpg size=300x300]] </td>
+<tr>
+<td> Not a very good termination </td>
+<td> Rather better. </td>
+</tr>
+</table>
+
+Repeating the measurement with the better 50R terminator shows much improved
+directivity (shock horror!).
+
+| | Directivity [dB] |
+| |------------------|------------------|
+| Frequency [MHz] | Poor termination [db] | Good termination[db] |
+|-----------------|------------------|------------------|
+| 1.80 | -44 | -54 |
+| 5.36 | -40 | -52 |
+| 10.11 | -38 | -50 |
+| 50.00 | -25 | -40 |
+| 145.00 | -14 | -33 |
+| 435.00 | -8 | -24 |
+
+[ZDC-20-3]: Characterising_a_coupler/ZDC-20-3.pdf
+[powermeter]: W7ZOI_Power_Meter
+
[[!tag radio]]