The diagram is a reproduction from instructions to perform an effective sensitivity test for a generic radio receiver. In our organization it's considered the proper way to do an effective sensitivity test for a receiver. My question is, what does the 6 db attenuator do in this case. It is true that the the input to the T coupler from the signal generator is capacitively coupled. The justification that I've been told is that the 50 ohm, 6 db coupler makes the input to the T look like a matched load. I don't understand why this would work, or why it would matter for the reliability of the test. From an EM perspective, I believe to the signal generator the T would "look" matched because the signal reflected at the coupler will have been attenuated 12 db on it's round trip. Although, to the receiver, the signal will be the same, just attenuated 6 db. So I really don't see how it will improve our measurement.