RF : need help ...

what does following terms means
1. whats is dBm ? wats the meaning of +ve and -ve dBm
2. what is RF sensitivity?
~niks~

dBm is a power level. You divide the power by 1 mW and take the 10*log of the resulting number. This gives you the power relative to 1 mW.

Sensitivity is the signal level required for a system like a receiver to have an output signal to noise ratio of some specified amount.



Someone else will have to describe +ve dBm as I have never come across it before. What context did you find it in?

Good explanation by Flatulent.

I will use an example to explain:

E.g. If you have an input signal of -133dBm. This means the input power is 133dB below 1mW level. Therefore in Watts, you have 5.02e-17watts according to flatulent formula. +ve dBm means you have a power level that is above 1mW.

My explanation to sensitivity similar to flatulent:

Sensitivity is the available input signal level for a given output signal to noise ratio. Sometimes also called the noise floor.

Cheers,
Element7k

Hi Guys
I had some of these same questions. So here's my additions.

X dBm = 10*log(Y Watts/.001Watts) and the reverse is
Y Watts = 10^{(XdBm-30dBm)/10}

don't get confused with dB.

30dBm = 1Watt
40dBm =10Watts

if you put 30dBm (Pin) in to a 3dB (Gain) Amp, you will get
(Pout)= 33dBm out
33dBm=2Watts
if you put 40dBm (Pin) in to a 3dB (Gain) Amp, you will get
(Pout)= 43dBm out
43dBm=20Watts

I also have not seen the +ve or -ve before.

Sensitivity can also thought of in a practical way as...
If you want a receiver to correctly receive %99 of the data you
send to it you must transmit the data a minimum (sensitivity) level
of X dBm. This is mostly done by using a Bit Error Rate Test (BER)

Hope this helps