Basic Internet Connectivity And Modem Help

[Hammer]

I got a Motorola SB6121 last October. Install went fine. Saw major improvement over old modem. Starting last week my connection has been dropping. I have to reboot the modem several times, it connects for like 30 seconds then drops, reboot again, works for 30 seconds, repeat. After about 5 or 6 reboots it will stay on for a day, a few days, a few hours. Then it drops again.

I called support 6 days ago, they remotely reset it. Worked until last night, then dropped.

Called support, they reset it. Worked until today, then dropped.

I reset it manually 5 times. It's working now.

The last time I asked support what's wrong they said "my upstream looks a little high, maybe a modem issue". So I checked the modem connection status page. My upstreams were all at 51dBmV last night...

Today after rebooting it several times I am getting two upstream channels at 51dBmV, and channel 3 is ZERO! Do I have a modem problem or cable line problem???

[Jim721]

Yes you have signal issues on your Upstream anything over 50 is to high. The newer docsis 3 moto modems are a good modem but they do not like high signal levels when I had my 6120 as soon as the up hit 50 dbvm i was kicked off the internet and the modem would try and reboot. My new Zoom 5341j Is alot more forgiving none the less I had a tech come out and my signals are all good now. You may need a tech visit to find out whats going on.

[EG]

What do the downstream power and the SNR figures look like ? Channel three is a channel that hasn't achieved "lock" status so it says zero.

[Hammer]

[EG]

Those are weak as well. Are there any excess/unneeded coax cable splitters in the line leading to the modem that can be eliminated/re-configured ? 

If there aren't any uneeded splitters that can be eliminated and if your coax wiring setup can't be reconfigured so that there is a single two way splitter connected directly off of the drop from the street/pole with one port feeding the modem and the other port feeding the rest of the house/equipment with additional splits as needed and you've checked all the wiring and fittings for integrity and tightness and refresh them by taking them apart then putting them back together again, then perhaps it's best to book a tech visit to investigate and correct.

[Hammer]

I will try changing some splitters/feeds. What values am I looking to improve exactly?

[i-am-nerdburg]

Generally, an acceptable signal range for a modem is:

Downstream (forward path): -7 to +7 dBmV.

Upstream: (return path):  >40 dBmV but <50 dBmV . Some systems tolerate levels as low as 35 dBmV.

Signal to Noise Ratio (SNR): >33 dB (higher is better)

[EG]

Thank you sir !

[Hammer]

So here's my setup:

Drop from street to a junction box on side of garage contains 4 way splitter supplied & installed by Comcast.

Feed A- 25ft to kids bedroom cable box

Feed B-  40ft to kids bedroom cable box

Feed C- 120ft to living room MODEM

Feed D- 120ft to living room splitter then 5ft to Tivo + PC tuner

Feed E- 120ft to living room Dish Network box (not on Comcast splitter)

I had Feeds C, D, E installed through a pvc conduit around side of house when I moved in here two years ago. Relocating the MODEM closer to the main drop on the side of the garage would require running CAT5 through that pvc conduit to my Router (which is IMPOSSIBLE). I guess I could get a wireless bridge.

Swapping Feed C + D => Not much different, upstream maybe even a little worse:

Should I have a Comcast Tech come out to the house???

[Hammer]

Removed the 4 way splitter. Connected only the MODEM from garage drop to 120ft Feed C. Numbers are close to perfect:

Guess I don't need to have a Comcast Tech come out and charge me for "inside wiring problem". How do I achieve good MODEM numbers and keep all my other devices connected???

[Hammer]

Tried another 4 way splitter that I had laying around, numbers identical to the Comcast provided 4 way splitter.

Installed 2 way splitter (120ft to MODEM + 3 way splitter [two bedrooms + Tivo/PC]). Got a tiny bit better numbers, but not near where I want them:

I will keep this setup for a few days and see if I get any drop outs, but I would like to know:

How do I get perfect MODEM numbers and keep all my devices connected?

Can/will a Comcast Tech tune my signal to be perfect at my MODEM (with splitter and all my devices connected)?

[i-am-nerdburg]

You could use a drop amp with an active return. If you put this one before the modem with your original configuration, you would be at a 8 dBmV down and 40dBmV up which would be fine. Most cable techs will tell you not to use a drop amp on a modem, but your signal is clean and you have a very long run of cable. Your only other option would be to physically move the modem closer to the garage and use the two way splitter.

[EG]

A tech visit may be advisable to check the drop from and the tap on the pole to see if they can locate where any excess attenuation may be coming from. Me thinks that your connection quality from the street should be better in the first place to allow for some of the extra needed splits / cable runs at your premises.

[i-am-nerdburg]

He's already at 5+ down and 40 on the return at the side of the house (assuming RG6 at 550Mhz). He may be able to gain a little more by having levels adjusted at the plant, but he's not going to overcome 7dB loss from the splitter, 6dB of loss from 120ft of coax and whatever the loss is from the drop. 

[Hammer]

What do you think about putting this right at the drop in place of splitters:

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=182-562

Electroline EDA 2400 4-port

Forward gain: 7 dB

Return path insertion loss: 7.5 dB 

Forward passband: 54-1000 MHz

Return passband: 5-65 MHz

Frequency response flatness: ±1 dB

Noise figure: 3 dB

[EG]

Just saying that maybe a savvy tech who is actually "on site" should determine if an amp is needed in front of a modem. Kinda' tough for us to *diagnose* this one from our armchairs.

[i-am-nerdburg]

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Hammer wrote:

What do you think about putting this right at the drop in place of splitters:

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=182-562

Electroline EDA 2400 4-port

Forward gain: 7 dB

Return path insertion loss: 7.5 dB 

Forward passband: 54-1000 MHz

Return passband: 5-65 MHz

Frequency response flatness: ±1 dB

Noise figure: 3 dB

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No, you need an active return.

[Hammer]

Ok, how about this one:

http://www.pctstore.com/RF_amplifier_CATV_amp_PCTMAB10154A_p/pctmab10154a.htm

[i-am-nerdburg]

That would work!

[Hammer · Accepted solution]

New numbers with Active Return 4 way splitter:

Looking good to me! Also improved my signal levels to my Tivo: Was 83-85%, now it's 90-92%. SNR went from 34dB to 36dB.

[kenstowe]

What type of active return 4 way splitter did you use?

[Hammer]

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kenstowe wrote:

What type of active return 4 way splitter did you use?

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http://www.pctstore.com/RF_amplifier_CATV_amp_PCTMAB10154A_p/pctmab10154a.htm

[kenstowe]

Another question.  I show only 1 channel up.  Channel 2.  Is that normal for Docsis 3?  I show 3 bonded channels down. 

[kenstowe]

Correction: 4 bonded channels down.  1 channel up.

[EG]

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kenstowe wrote:

Another question.  I show only 1 channel up.  Channel 2.  Is that normal for Docsis 3?  I show 3 bonded channels down.

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Yes. It can be. It depends on how many upstream (return) channels are actually present / configured on the local system. You could try powercycling, or if need be, resetting the modem back to factory defaults to see if it picks up any more bonded upstream carriers.

[kenstowe]

http://www.pctstore.com/RF_amplifier_CATV_amp_PCTM​AB10154A_p/pctmab10154a.htm

Just tried to order this and it has been discontinued.

[Hammer]

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kenstowe wrote:

http://www.pctstore.com/RF_amplifier_CATV_amp_PCTM​AB10154A_p/pctmab10154a.htm

Just tried to order this and it has been discontinued.

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I actually got mine at Amazon:

http://www.amazon.com/PCT-4-Port-Signal-Amplifer-Active/dp/B005P12QME/ref=sr_1_1?ie=UTF8&qid=1337892...

[kenstowe]

I actually got mine at Amazon:

http://www.amazon.com/PCT-4-Port-Signal-Amplifer-Active/dp/B005P12QME/ref=sr_1_1?ie=UTF8&qid=1337892...

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Thanks.  One is on the way.

[Jim721]

EG.. Im still new to all this Cable/Internet stuff i only found these forums from having constant issues like others. Im just wondering has it come to the point were we as customers have to pay for and fix our own stuff?? This just is not right.

[kenstowe]

http://www.amazon.com/PCT-4-Port-Signal-Amplifer-A​ctive/dp/B005P12QME/ref=sr_1_1?ie=UTF8&qid=133789...

This amp did the trick.  Downstream power level runs between 6-10.  SNR 37dB.  Upstream power levels run 43-45.  Every thing is stable and no more drop outs and reboots.  Thanks for the help.