Yes, very true. Systems who use excessive cascades for their HFC networks NEED to have limited cascades (maximum 6 to 8 deep) or suffer the concequences of CTB/CSO issues. What many do not know is the amplifiers used in the HFC network are nothing more than 2 or 3 output line extenders as compared to the old "Trunk and Feeder" mainstations of the 1990's and earlier that had distortion controlled output levels. By this I mean the trunk output (32/29) and a bridger output (45/38) would produce different distortion levels. The trunk produced lower distortions and could be cascaded beyond 20 deep. The bridger/feeder was limited due to the higher output and could only be 1 or 2 line extenders in cascade...if derated by 3dB this would keep the distortion content at an acceptable level.
Keeping that in mind, to cascade a SAII, SAIII, GNA, TNA, Gainmaker or similar amplifier beyond 6 to 8 deep, would not be recomended because of created distortions. You would expect to see problems past the 6th amplifier regardless of how flat or correct it is balanced for this reason. As bad as it sounds, if someone was going to have a cascade of 12+ deep, they would have better luck with the old SAI Mainstation or Magnavox Mainstation...but they only went to 450/550MHz unfortunately. Another "bandaid" for this type of long cascade would be to get rid of all the analog carriers and use digital carriers at a lower level. You would still need bandedge analog balancing carriers and sweep the spectrum flat. I am not suggesting using these old Mainstations for many obvious reasons, but anything over 6-deep in cascade there is potential for problems.
Re: Added Channels In Fm Band
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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