In Reply to message #373150 by bob scott
Old School Member Buffalo Chips is not online, or is invisible.
6/1/2017 9:55:23 PM
Buffalo Chips Member #: 7190 Registered: 1996-2001
Posted: 435 View all posts by Buffalo Chips
Company: Interactive Broadband Technical Services Occupation: HFC Engineer/Consultant Location: www.interactive-broadband.com
Re: return laser clipping
Hi Bob,

Laser clipping can be caused by a wide varity of issues. Bottom line (and simpley put) it is due to RF overdrive at the laser input. The input to any laser is typically rated in power, NOT a specified dBmV input level as the combination of RF, ingress, noise and other unwanted garbage adds to the overall total input power level. This is what basically generates laser clip and/or overdrive. You may find a specified RF input by some manufacturers BUT a correction must be made for the allowance of unwanted ingress and noise that unfortunately is always there to some degree.

The best way (and only way in my expert opinion) to determine if you have clip in the optical link in EITHER direction will require a SPECTRUM ANALYZER to observe the entire noise floor and RF spectrum being used (and some leg work). Forward optical links can and often do result in clipping but it is more common on the return optical link.

The return optical laser usually has a 5-200 MHz input bandwidth but in a sub-split system here in the USA, it only uses 5-42 MHz for the most part. Nonetheless, there is potential for many issues to cause clip.

As how to identify and troubleshoot if a laser is in clip, well, I could write for hours about that subject!

Please call me on my cellular or email/PM so we can talk. I was a field engineer with Philips Broadband and Scientific-Atlanta in the old days and dealing with clipping lasers was a never ending issue that had to be corrected. I can give you some good pointers on where to start.

Thanks,

Greg Tobin
Interactive Broadband Technical Services, LLC
gtobin@interactive-broadband.com
(-REDACTED-) cellular
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1 Replies
9/1/2017 12:02:37 PM
bob scott