Element 8 Question 287

Question:

[EL8-287] A directional coupler has an attenuation of -30 db. A measurement of 100 microwatts at the coupler indicates the power of the line is:
 
a}  10 watts.
b}  100 watts. [Correct Answer]
c}  1,000 watts.
d}  10,000 watts.

Challengers Excerpt:

"A directional coupler has an attenuation of -30 db. A measurement of 100 microwatts at the coupler indicates the power of the line is:"

It says 100 watts....should be 100mw. -30db equates to /1000 a^x=b
(10^3.0=1k) from 10 log 1000=30

Response:

I believe the question inadvertently stated microwatts when it should have stated milliwatts. However, the analysis is correct in the challenger's excerpt.

Recommendations:

Change the question to

[EL8-287] A directional coupler has an attenuation of -30 db. A measurement of 100 milliwatts at the coupler indicates the power of the line is:
 
a}  10 watts.
b}  100 watts. [Correct Answer]
c}  1,000 watts.
d}  10,000 watts.