The Cougar superiority comes from the low gain and high output level. Since it can put out ~20 dBm without distortion and has a gain of +10 dB, it can handle inputs with +10 dBm.
The other two amps can only handle inputs of around -10 to -5 dBm before they saturate highly. So the true noise performance is actually worse for those once you consider our setup:
namely, that we have a gain of 10 opamp ahead of it which is putting out ~20 nV/rHz of noise at all times. *So the difference between 1 dB NF and 3 dB and 5 dB is totally inconsequential.* The 3 dB NF is just an input noise of 1 nV/rHz.
In reality, the transmission readout doesn't need any of these since the signal is so large. The PDH diodes will have in-loop signals of somewhere between -10 and 0 dBm going into the Cougar. I believe we can only use those high gain, low output power RF amps in the case where we have very low light. |