Hi Gary!
I just got back from SE Asia and the West Coast a few days ago and had to say "Merry Christmas"! Besides I had to put my 2-cents worth in! I know that you understand the following but I am doing this for the other readers.
After reading a few comments on this thread, the term "Self Terminating Tap" is only correct IF and ONLY IF the individual that is working on that tap "He Himself Terminates" the tap ports with a 75-ohm port terminator. Otherwise, it is the same as a house splitter with an open port. The only difference between a 2-way house splitter and a 4/2 tap is that the tap ports "block" the AC from the "f-ports". The same goes for a 4-way house splitter and a 8/4 tap ect.
As for the intermittent noise levels being seen at the CMTS, this is all "smoke in mirrors" if the technician is not logically troubleshooting to the best of possible senerios. First of all MANY cable companies make a mistake looking at SIGNAL-To-NOISE RATIO as seen by the modems vs. the CMTS and should be looking at CARRIER-To-NOISE RATIO at the headend at the return RX to determine specific problems. CNR is physically looking at the reference carrier to the actual noise floor of the system at the output of the specified return receiver. The same for Carrier-to-Ingress looking at the exact amount of interfering carriers to the noise floor.
There are MANY diferent possibilities that can cause SNR to look bad and actually a good CNR exists and visa-versa. This all has a relationship to keeping correct plant design, levels and house installation losses within a desired specification window. How many times has a technician changed out a pad, equalizer of tap faceplate value to make the SNR look good at a single home and screwed up the other 50 customers? More common than a snow storm in Buffalo in January.
To make a long story short, there are various factors that can cause CPD, noise, ingress, bad CNR, and bad SNR. Unfortunately there is no easy fix unless a very good preventative maintenance and through training program is put in place to avoid such issues that can be controlled. In my exerience, yes there are many problems caused by the decay of the outside plant, but unfortunately the majority of problems found in the field are "man made" problems that could have been prevented. That is why training is important and crucial in todays networks.
Another major factor that many miss is the OVERDRIVE and CLIPPING of the optical transmitter in the node. This problem displays excessive distortions that may or may not be seen in the field. Optical overdrive is a MAJOR contributor to many problems and unfortunately technicians chase "ghosts" in the field when the main problem is at the input of the TX. That is another topic!
Sorry for the soapbox, I have not posted for a while and just wanted to add a few comments!
Merry Christmas everybody!
Greg Tobin
Interactive Broadband Technical Services, LLC
Re: Return Path
Member #: 7190
Registered: 1996-2001
Posted:
483
Name:
Greg Tobin
Name:
Greg Tobin
Company:
Interactive Broadband Technical Services
Occupation:
HFC Engineer/Consultant
Location:
www.interactive-broadband.com
Personal:
Experience:
~45 years
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