Hello Ravil,
I had a similar doubt on using a 3R Generator + BER analyzer over connecting the data signal from the transmitter end to the BER analyzer at the receiver. From Damien’s post I am assuming that we use a 3R generator mostly for simplification of the layout.
To compare a 3R Generator + BER analyzer with a BER analyzer with connections from the transmitter, I used them simultaneously in a sample project simulating a simple RoF System. What I observed is that the Min. BER using a 3R Generator was much higher than that without a 3R Generator, e.g., 10^-5 as against 10^-8 respectively.
I also compared the two schemes for a back-to-back connection against a system with a 50 km long SMF between the transmitter and receiver. The Min. BER using 3R Generator was always higher. Damien has also pointed out that the noise may play a part. May be that may have a role to play because of using MZMs, power combiners, EDFAs in the system I designed. It is attached here.