HP 778D Dual Directional Coupler - Tear Down 

I discovered your channel as a result of your guest video on eevblog. I am devouring your videos now and loving them! Now, I'm not an EE, but at 28:30, I don't think it's return loss that you're measuring, but rather the coupling effect of a full reflection. In other words, nearly 100% of the energy is reflected from the open connector, back into the device and then the coupling port is picking that up, less 20 dB. Your reading of -21.35 dBm is the original 0 dB relative baseline, minus the 20 dB coupling factor, minus 0.3 dBm insertion loss from the device, minus odds & ends from imperfect reflection, drift, etc. So the Minicircuits chart really isn't meaningful in that context and the VSWR of the open is closer to 1:∞. Please correct me if I'm wrong. Thanks a zillion for your great videos!

Great vid, obviously you have been reading up a lot about RF stuff, good work! I saw you where spinning the male load a bit when you connected it to the directional coupler, always try not to do that. The tounges on the female connector have sharp edges and acts like a lathe which turns the plating off the male pin, only the collar should be turned when connecting RF connectors :)