I am sorry, but with 18 to 20 dBmv input, you are asking for trouble. Most return IC have a 4 to 5 dB noise figure and with a 15 dBmV in put that give you a 69 dB C/N per station, you do not require a much better C/N. But with 20 dBmV input and your cable modem having a 55 dBmv max output, with 15 dBmV input you have about 8 dB play for the cable modem output but with 20 dBmV that range is now down to 3 to 4 dB range. Do not forget cable modem have their output controlled by the CMTS and the worst placed to have problem is the first multi tap, where you should never go higher than 27 dB for this multi tap value. I have seen system still using 30 dB multi tap value and do not understand why they having problem.
That remind me of any spec given for HFC product manufacturer, if they give you the distortion at 52 dBmV, it doesn't mean you have to use 52 dBmv as their actual output level. This industry (CATV) has always used a lower operating level for theirs specifications and my theory has always been, try to stay away from system noise as much as possible by using a better input. Specialty true with to-day IC, which are more better that the one used a couple year ago.
Just my taught after been in this industry for over 50 years.
Re: What do you do to improve snr.
Member #: 3359
Registered: 1996-2001
Posted:
1285
Name:
Andy Lamarre
Name:
Andy Lamarre
Company:
Catv Expert
Occupation:
Dir.
Location:
Montreal, Quebec, Canada
Personal:
Ancient
Experience:
~66 years
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