CABL Forum - Re: SNR Issues Cable Modems Drop Small System

your system needs to be set up correctly. From what I understand You hired a contractor to check for noise? But if your feeder is not set up correctly your modems will not work for long.
Usually they will work at first but as more modems are added the window gets smaller.
If a feeder leg is running 8 db hot you just amplified your noise level by 8 db. Lets say the modem wants to run out at 45 db on the return. Just do the math. it goes thru a say 4 way splitter, 200 ft of rg6 cable, a 14 tap, then insertion loss thru a 17, 20, 23 tap, the feeder cable, then into the le. your want 20 db hitting the le(or any amps in between). Now if your system is not set up correctly and the le is 8 db to hot, you increased your noise by 8 db and you lowered your modem injection level by 8 db, it is a double wammy. The modem gets its loutput evel from the cmts and if the path between them is set up incorrectly the cmts cannot properly control the modem.
Go to the node, or the first amp if your not running fiber, and inject the proper level.( from the tech spec of your equipment) have a tech in the head end set up the receiver to the proper level. Contact your distributer and find out the proper set ups of the node that your running. Once you get that link set up and you have the level of your injection from the node as proper then move to the first trunk amp out. You need to know the proper set up of your equipment. you cant just stick a pad in. inject the same level at the trunk amp as you did the node or first amp out, pad the amp to match the receive level of the tech in the head end. If your 5 db hotter at this amp than you were at the node add 5 db of pad. once you get that link set up move to the next amp and do the same thing, always keeping the level hitting inside the head end the same. Always pad the return output. You said the return in the les were factory set and that concerns me, there is know way they could even be close.
5 db off on the return means a lot. again it costs you twice to be off. especially to hot. Your modem lowers its injection and the noise is over amplified. if your cmts is receiving to hot of levels it tells your modem to decrease its output, if you want 20 db hitting the le off the modem and the modem only has to transmit 32 then do the math, if your hitting the first le with 8 db then you can imagine whats happening to the carrier of the modem.
same concept as the forward. If you had 8 db inputs to the forward of an le, yea you might can over amplify and get your levels but wont be watchable after it goes thru a few amps.
you cannot pad at the cmts and tell anything. all your changing is the transmit of the modem. if the system is not set up right putting a 10 db pad at the cmts can only make the problem worse. You have a cmts, a reciever, a node, a trunk amp, a le and a modem, they all have specifications and any deviance from that spec degrades signal quality. Modems are very forgivable and usually will run when there are only a few out there. each one you add closes the window. once your at a certain point where just the right amount of traffic is on your network it will shut down. Sounds to me like thats where your at.

Remember that modem operates best at 45 or so output transmit level. do the math at the house to the first le. You want 20 going into the le. if the modem puts out 45 you will have a total of 25 db of loss from modem to le. Hopefully you guys did proper installs of the modems. Bad installs are the worst. once you know that is correct you can just follow that 20.
Like another guy said, your running 2 systems now.
I would say if you guys are not sure how to properly balance and maintain your system right now you would be best off to hire a consultant to come to your system, evaluate it. Tell you how to fix the problem at hand and then the proper way of maintaining your new communications network. The worst thing to do in todays market is to drop the ball on a new service. If your in a small market and your service is less than perfect then your going to lose subscribers and well you know the rest.
It is impossible for anybody here to do much more than guess at what your problem is and to be honest from the sounds of things and from my past experience dealing with systems that sound familiar to yours is that you have just about every problem there is to be had. And not sure how to deal with them.
You need a consultant, there are many to choose from. Just make sure you know the guy your hiring knows his stuff, and yours!.
If you have a good system, tools and equipment, and a decent technical staff it would not take long for a good consultant to fix your problem and teach you how to prevent them from happening in the future. May cost you a little cash today but will make you money in the long run. As a local tech you should be willing to do your part and take advantage of training. I know if somebody had something they could teach me to make my job better, and it was something I wanted to learn I would pay him to show me.
The company would be able to profit from the service training by keeping satisfied customers, better quality work from there technical staff. And a leg up on the future advances of communications networks. Haha ok I dont know anything about cable tv, But I did stay at a Holiday Inn express last night.
But for sure man good luck and shout at me if there is anything I can do. What system do you work for?

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Re: SNR Issues Cable Modems Drop Small System