Greg, I once had to work on a cascade of 86.......Trunk amplifier deep, where the C/N at the end was around 39.2 dB when all the amplifiers were in good working condition. That is call a miracle or stupidity depending how you are looking at it, but this is the way the industry taught in the old day. If you were to add an amplifier with 60 dB C/N, the end of that cascade, the C/N would only degrade by 0.01 dB, where the final C/N would still be around 39.2 dB.
I agree, with today HFC system, where the last amp. on the system should deliver around a 48.0 dB C/N and adding an amp. with 60 dB C/N, the noise addition would bring the 48.0 dB C/N to be 47.8 dB or worsen by 0.27 dB.
