...That there IS a difference between "High End Roll-Off" and "low inputs due to Cable & Passive Loss". Many people use the term "High End Roll-Off" very loosely.
There are many good responses on this thread and I just want to go a bit more in-depth. Sorry for the rambling in advance!
If your plant design was correct and cable placed (along with amplifiers and passives) in the correct areas, if you use 750-MHz amplifiers in a 860-MHz design or 860-MHz amplifiers in a 750-MHz design AND the designer/re-designer has utilized the amplifier GAIN differential AND the proper equalizers used along with proper alignment carriers at the band-edges, it should work. Higher gain amplifiers may be needed to keep current spacing and output level and tilt be changed to accommodate existing design criteria. If you have the gain, you have the level. If not and the design is correct, there is a problem that needs to be repaired.
This is no different than dropping high-gain 1-GHz into a standard-gain 750-MHz system or a high-gain 550-MHz into a standard-gain 330-MHz system. Going the opposite direction would produce obviously more level and gain for the cable spacing depending on the gain of the amplifier.
Keep in mind that if you change amplifier bandwidth(s), you must do the math and possibly need to change the output levels of the amplifier and the gain of the amplifier used at specified frequencies to allow the existing plant to function properly. There are too many variables to list here but if a technician is familiar with the basics (cable loss) and how to identify actual "roll-off" and "over-spacing", he will be able to find and repair (or document a design error) if a problem does exist.
If a design is changed as previously mentioned, THE EOL CALCULATIONS SHOULD ALSO BE CHANGED TO REFLECT THE NEW RE-DESIGN CRITERIA.
Unfortunately, many point fingers to "bad cable" or "high loss cable" when in fact, it is either something as simple as a bad splitter or tap, corrosion in a connector due to water migration, bad or wrong bandwidth equalizer or a poor design. There is a possibility of bad cable but the utilization of a TDR and a simple cable loss chart for specific cable will prove most effective for the technician as long as he is trained to use them properly.
Using a SWEEP properly will also reflect the "roll-off" (if it does exist) as one needs to see the entire bandwidth signature (not a signal-level-meter) to determine such providing a PROPER reference was achieved. Being familiar with bandwidth compression, reflections, RF grounding and knowing how to correct and identify such problems is imperative to the sweep procedure. There are "Sweep Technicians" who will find and fix problems and there are "Picture Takers" who just fly through a network just for documentation. But that is a different story.
If you need any further assistance, please call.
Good luck.
Greg Tobin
Interactive Broadband Technical Services, LLC
314-422-4423 cellular
Re: High End Roll Off - No One Has Mentioned....
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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