Well 1st of all, you need to FIX the ELEVATED NOISE FLOOR. Looks like a basic return balance for starters. After you achieve that step, then locate and fix whatever noise and beat products are left.
In basic terms, your possibly BLOWING THE PISS out of the return laser, aka "CLIPPING THE LASER". Whenever you go over 100% input drive to ANY laser, beat products show up in the strangest places and many times create the illusion of CPD. Remember, YOU CAN NOT DESTROY ENERGY, it just shows up as beats whenever you exceed 100% power input drive. The severity of the beats depend on the amount of level being introduced into the laser AND NO TWO CASES ARE IDENTICAL. (Just in case someone will contradict my theory). If you ONLY see this at the optical receiver output and NOT at the laser input at the node, this could be very well what is happening.
A simple test would be to instal a 3dB pad at the input to the laser. If the noise floor and beats drop by 3dB at the receiver output (1:1), you are not in "clip". If the problem SIGNIFICANTLY improves, this is telling me that you have a "clipping" issue at the laser. REMEMBER that installing a 3dB pad will reduce the laser input drive by 50%. Like a 2-way house splitter, 50%/50% each leg = 3.5dB/3.5dB (3.01dB/3.01dB in theory) each leg OR a power divider/splitter. When you do ANYTHING in cable by 3dB it either INCREASES or DECREASES by 50% of the power. This is the basic "Rule of Thumb".
There "may" be some CPD in this graph, but I also see many other beats and carriers beyond the 6-MHz spacing. Many people chase GHOSTS and blame it on CPD specifically when it is INTERMITTENT and they can not find it. When they drop a faceplate or pull a pad, this is DIRECTLY PROPORTIONAL in many instances to reducing the drive to the laser when it is in "clip". That is why training on this topic is important for the technician as he must understand what is happening before he can fix it, or he will be spinning his wheels.
I can not say for sure that this is the problem you have been experiencing in this case, BUT, using the simple troubleshooting I just mentioned above should help you solve this issue. Call me if you have any questions.
Good Luck!
Greg Tobin
314-422-4423 cellular
Interactive Broadband Technical Services, LLC
Re: help with ingress? "CHECK FOR CLIPPING&am
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
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Experience:
~45 years
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