If I have theoretical system where thermal noise is input to an amplifier which has a gain of 20dB and a noise figure of 3 dB, I should see a 3dB rise in the thermal noise, correct?
Conversely, if I have a system noise of say -125 dBc/Hz, I should see an increase in that system noise by 20dB, correct?
2007-03-19 10:18:57 · 2 answers · asked by Anonymous in Science & Mathematics ➔ Engineering
Neither. An amplifier amplifies thermal noise by the sum of its gain and its noise figure.
You should see a 3 dB rise in thermal noise on top of the 20 dB gain, that makes a total of 23 dB gain of thermal noise for 20 dB gain of signal power (provided your input SNR is greater than the noise figure, if not the noise figure will scale down to make the output noise power not greater than the output power.)
2007-03-19 11:03:46 · answer #1 · answered by sciquest 4 · 1⤊ 0⤋
It amplifies both signal and noise by it's gain. If you had a perfect amplifier which added no noise of its own to the signal, the SNR of the signal would be the same after amplification as before amplification.
Noise Figure is a measure of the additional noise added to the signal by the amplifier.
Doug
2007-03-19 10:52:32 · answer #2 · answered by doug_donaghue 7 · 1⤊ 0⤋