Can anyone actually explain to me how this mathematics question was does as I had it in an engineering test?/?

Question

Can anyone actually explain to me how this mathematics question was does as I had it in an engineering test but couldn't do it, also could you explain it to me step by step, how to do log bases ect on calculator as I have no idea:
The power gain of an amplifier relates input power, Pi, to output power, Po, by;
Power gain= 10log(small 10) Po/Pi decibles (dB)
a) As part of the assesment of a new system you have been asked to find the power gain when Po=18W and Pi=300mW
B) you also have to find out what the output power will be if input power is 400mW and the power gain is 20dB.


Please may someone explain this to me step by step as it completely mindblows me, thanks to anyone who can help me it will be much appreciated.

Thanks everyone :)

Answer 1

Wow, i can't beleive you are asking this question again. Just refer to your previous posts.

Answer 2

Gain in decibels=10log[Po/Pi] to base 10
a]gain=10log[18/.3]=10 log60 to base 10
=10*1.778=17,78
b]let the out power=Po
Pi=400mW
Gain=20 Db
20=10log[Po/.4] to base 10
Po/.4=10^10
Po=.4*10^10 Watts
=4000 mega watt

Answer 3

Let Power gain be PG.
Write log with subscript 10 (log with little 10) as log.
a) Note: 300 mW = .3 W
PG = (10 logPo)/(Pi) = (10log18)/(.3) = 4.2, to one decimal place.
b) By a), 10 logPo = (PG)(Pi)
Thus, logPo = (PG)(Pi)/10
Po = inverse log[(PG)(Pi)/10] = 10^[(PG)(Pi)/10]
= 10^[(20)(.4)/10]
= 10^[0.8] = 6.3
You can put in the units. I am only interested in seeing the math process...

Answer 4

I can give you some basics. dB is a logrithmic measurement not linear. 3dB is a 100% increase in power. 18DB would be a 600% increase.

Answer 5

ask my friend sam, he's great at maths, 0208 555 6628!!!!!!!

GOOD LUCK!!!!!