added zdc-20-3 directivity measurements with better 50R termination

[wikirepo] / notes / Characterising_a_coupler / index.mdwn

diff --git a/notes/Characterising_a_coupler/index.mdwn b/notes/Characterising_a_coupler/index.mdwn
index b989289..99f64c5 100644 (file)
--- a/notes/Characterising_a_coupler/index.mdwn
+++ b/notes/Characterising_a_coupler/index.mdwn
@@ -49,4 +49,34 @@ might blame the 50R termination as any reflected power will be seen in this meas
 
 [[!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]]