Starting point
I borrowed a 2m / 70cm diplexer from a fellow HAM to connect my Multiband-2m/70cm-Antenna to my IC-9700. The IC-9700 has a 2m and a separate 70cm port - the antenna a single port - thats why I need the diplexer. 
The diplexer is a german manufactured AUTH EM 702.
Measurements
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The diplexer was not really working. The 2m path works so far with the expected TL of 0,3dB. |
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| But the 70cm path was not working. A TL of 40dB is not expected. |  |
Equipment
I was using my SV4401A VNA to do the measurements 
Fixing
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I heat up my soldering iron to remove the base cover. In my opinion, this reveals a major soldering mess - but I think positively and assume that at the date of manufacture there were no means of removing the flux and that solder did not yet adhere very well :-/ There was a intermittent short between a capacitor und the ground - quality control, so important. |
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Validation
After fixing, the measurements where as expected:
| The path from the 2m port to the antennna port |  |
| The path from the 70cm port to the antenna port |  |
| The path from the antenna port to the 2m port |  |
| The path from the antenna port to the 70cm port |  |