Motorola RNG150N STB upstream signal levels - AVS Forum
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post #1 of 11 Old 10-21-2013, 06:19 AM - Thread Starter
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Good Morning All
I was wondering what is the Ideal output upstream level for these boxes to get back to the comcast headend.
Currently have 20 STB's in an office and they all seem to drop out or lose authorization and then need a rehit.
The in coming signal is perfect about 0 to 2db into STB's but they seem to be putting out (upstream) 60db according
to diagnostic menu #7. Is this the max ?
Thanks in advance for any advice
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post #2 of 11 Old 10-21-2013, 11:00 AM
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The Forward Data Channel (FDC, control data from the Headend) and Reverse Data Channel (RDC, control data back to Headend) operate the same as a DOCSIS 2.0 Cable Model, using QPSK. Since RDC uses a much narrower bandwidth (about 250 kHz), many RDC's can be packed into the 5-40 MHz Uplink Bandwidth.

The Headend controls the level of each and every STB and DOCSIS Cable Modem so that the level AT THE HEADEND is maintained at the SAME level, thereby minimizing Intermodulation Distortion between the narrowly spaced RDC frequencies.

Although the exact wording is rather complicated, DOCSIS 2.0 (and 3.0) Radio Frequency Interface Specifications stipulate a 58 dBmV MAXIMUM output level for Cable Modems...and hence also STB's.
http://www.cablelabs.com/cablemodem/specifications/specifications20.html

Here is a more detailed summary:
http://www.dslreports.com/faq/16085

"Drop Amps", frequently with 4-port or 8-port RF Splitters built-in, are used to overcome RF Splitter Insertion Loss. However, since they usually amplify ONLY the downstream, the multiplicity of STBs at your location must try as hard as they can to push an RDC signal back to the Headend through that same network of Lossy RF Splitters.

If the RF Splitter Network and associated Drop Amp(s) are your responsibility, be advised that 4 and 8-port Drop Amps can have various level of Reverse Insertion Loss (up to 8 dB for some 8-port Drop Amps), while others provide a small amount of Gain for the RDC signal. You might want to replace your Drop Amp(s).

If you don't own the Drop Amp(s), you should have a COMCAST tech take a look at their system to see what they can do to improve the situation....perhaps they have an alternative Amplifier with Gain in BOTH directions.
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post #3 of 11 Old 10-25-2013, 09:22 AM
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Typically you want to be 46-50dbmv U/S.
Did Comcast set up the distribution in your office?
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post #4 of 11 Old 10-25-2013, 12:42 PM - Thread Starter
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No comcast only provides a demarc point/ tap in the main building. We maintain the Campus wide distribution via fiber and coax. For the most part all stand alone stb's have been fine. The somewhat problematic (20 total) ones are all colacated and have been running without
issues for close to 2 years. Recently though I have returned to find the picture frozen or pixalating on different stb's.
I am going to try feeding one of the stb's directly from the spare port on the tap to see if the upsteam level comes down from 60 and post the results about a week from now.
Thanks for everyones help
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post #5 of 11 Old 10-31-2013, 09:07 AM
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From your de-marc tap what else is in line all the way to each STB?
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post #6 of 11 Old 11-01-2013, 12:29 PM - Thread Starter
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The demarc/tap goes directly into an amplifier that feeds a 4-way splitter, 3 of the 4 ports go to other buildings on campus. the 4th port is then connected to a 2-way splitter that feeds 2 12-way splitters that then feed the 20 colocated STB's. When first installed 2 years ago we were hitting the STB's with too much forward signal so we had to put in attenuators. We know that the attenuators also effect the return path.
The amplifier has an option for active return path gain(up to 18dbmv) which we will try next and post the results next week.
I have the same provider at our office and since Tuesday our STB has gone down 2db each morning. It started at 60db, went to 58 on Weds, 56 on Thurs, and is at 54 db today. Im hoping its below 50 by Monday 11-4-13.
Thanks for everyones help and useful links
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post #7 of 11 Old 11-01-2013, 01:00 PM
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What is the Mfr/Model Number and TOTAL REVERSE LOSS/GAIN for the return signals through the Amplifier/Splitters??? Are they cascaded and if so how many times???


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post #8 of 11 Old 11-05-2013, 05:14 AM - Thread Starter
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the first amp is a BT860 with a 18 db reverse gain that was not used at first.(2 plus years ago) We seem to be getting better results now With the return activated but there only in 2db increments everyday. Looking @ 2 stb's one is at 40 on return the other is at 50. I will wait to the end of the week to report the readings
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post #9 of 11 Old 11-20-2013, 06:06 AM - Thread Starter
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Hi everyone
they now want to add an internet modem(comcast) I think i could do this via 2 way fiber .Any thoughts ?
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post #10 of 11 Old 11-20-2013, 09:09 AM
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Quote:
they now want to add an internet modem(comcast) I think i could do this via 2 way fiber .Any thoughts

A modem to feed all or just a specific area?
(2 way splitter or power divider not fiber.)
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post #11 of 11 Old 11-20-2013, 12:45 PM - Thread Starter
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This would be a modem to fill one outside vendors need.(not the customer) so yes just one specific area on campus for now but there may be request for more ? It has to be fiber due to distance on campus and no other pathways. They currently have 2 modems up and running in separate buildings for others to log into. These however are fed via coax(only about 600- 800 feet away from tap/demarc) and going through .750 0r .500 cable
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