In a message dated 97-02-21, you write: << NTR 3 network has little effect on achieving decent transhybrid loss. It's nothing like the effect the Austel complex impedance network has on THL. >>
Duane: Thanks for your feedback. I'm surprised that you see any significant difference between the NTR 3 network (275 ohms, 750 ohms, 150 nF) and the Austel network (220 ohms, 820 ohms, 120 nF). Are you sure that there is a difference? The old BS 6305 network was a problem (370 ohms, 620 ohms, 310 nF), but this is now history. BTW, I have had the same experience as you with optimizing THL with a complex return loss termination. It just seems to be easier to get decent results when the return loss termination is 600 ohms. I'm not sure why. Partly because of this, I prefer to use a 600 ohm termination for the designs that I get approved under NTR 3. The test report does not look as impressive (only about 2 dB margin at 4000 Hz), but it gets the job done. As we have discussed, I do not believe that this poses any tangible threat to actual, real-world performance. Joe Randolph
