I'm having a difficult time trying to solve something that should be very easy.

Question

I have the following:
40dBm - 6 dB + 10dB - Lprop > -100dBm

Now, the answer should be Lprop < -144dB, but I'm getting messed up with the signs.
I'm trying to move the -100dBm to the left part of the inequation and I think there is where I'm doing it wrong. If I move it to the other part with a + signus, then I'm adding dBm with dBm and, that doesn't make sense, as they would be mW^2 and Lprop is unitless.

What should happen somehow is that I would need to substract dBm - dBm in order to get dB, but I can't figure this out.

Could someone make the solution of this step by step and providing as much information as posible? That would be of great help thank you!

Answer 1

40dBm - 6 dB + 10dB - Lprop > -100dBm
are you solving for Lprop?
-Lprop > -100dBm - 40dBm + 6dB - 10dB
-Lprop > -144 dBm - 4dB
Lprop < 144dBm + 4dB

Answer 2

40dBm - 6 dB + 10dB - Lprop > -100dBm
Your dBm's will never cancel out... regardless of what side you bring them too.
Do you have to convert your dB's to dBm's first??
hmmm....