Originally Posted by videobruce
tiling (pre/post corrections)
Let's take 64/256 QAM for this explanation: You have several parts to a digital signal; the RF signal strength,MER, and the measurement of the MER over a period of time = BER. In the BER measurement you will have the total power and Bit rate of that QAM 38.8 Mbps and with a good quality meter look at packets that can be corrected in the stream and process them thru=Pre Errors. Packets that can not be processed thru that are un-corrected are= Post errors, these are what we see and hear with corrupt digital signal = tiling, blocking, freezing, and audio break up. Actual RF signal in digital is one small part, the bigger measurement is MER 35> for 256 QAM should be the lowest. BER test should be done over a period of 5-minutes> to get a good idea of the quality of the signal over a period of time and give the user of the equipment a better idea if there are any Pre/Post errors.
In a CATV plant the amplifiers that are used to amplify the signal more than likely have 2-3 amplification points (Hybrids) Techs will pad and Eq the inputs for flatness and than pad again to get a desired output. Too little input to the amp will give bad MER/BER results and over-driving an amplfier will do the same. There is no magic number just a cliff effect of either good or bad here.
Analog is more affected by visible artifacts due to seeing the C/N increase = good picture. Or decrease <43db C/N and less noisy picture. Beats from over driving an amplifier CSO/CTB where very common in the 80's but with Node + 3,4,and 5 runs is not seen anymore. FCC POP test are still done on those with analog systems and I have yet too see any large CATV not hit their numbers.