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New Visitor
Posts: 14
Registered: ‎02-18-2004

What is 64 to 256 QAM?

I've noticed that people on the forum have mentioned Comcast changing from 64 to 256 QAM. I assume this is some sort of upgrade. How can we tell if this was done in our area? I have been experiencing connection issues recently, and they seem simlar to those of people who have had the QAM change recently.
Most Valued Poster
Posts: 1,408
Registered: ‎10-27-2003

Re: What is 64 to 256 QAM?

You won't. It is a upgrade. Unless it causes your Cable Modem to stop working. It is not something you will see or be able to tell.
New Visitor
Posts: 14
Registered: ‎02-18-2004

Re: What is 64 to 256 QAM?

It has apparently caused a problem with my connection/modem. Any constant-bandwidth programs (like online games) will only stay connected for 1-5 minutes before disconnecting. For several years my connection has been rock solid, and apparently much faster than most people's cable connection (according to the tech support guys in my area), but suddenly in the past couple weeks, this new problem has arisen. It affects all games, and I have tried it with and without my router connected, and on different computers. I believe it might be the modem or my signal. How can I tell?
New Visitor
Posts: 12
Registered: ‎11-14-2003

Re: What is 64 to 256 QAM?

Hopefully you can check the diagnostics of your modem to determine what the QAM is.

There's a FAQ (http://www.dslreports.com/faq/comcast) on dslreports.com forums that tells you among other things, how to access several differnt modem's diagnostics.

http://www.dslreports.com/faq/7363
Most Valued Poster
Michael
Posts: 6,099
Registered: ‎06-30-2003

Re: What is 64 to 256 QAM?

QAM upgrades will only impact your connection if your SNR is borderline or too low. In other words, QAM 256, is more sensitive to niose than QAM 64. Your best bet is to contact us and have the tech run diagnostics on your line to see if your signal levels look good. We can always send out a tech if needed.
Most Valued Poster
Posts: 1,408
Registered: ‎10-27-2003

Re: What is 64 to 256 QAM?

You can check your cable tv stations, channel 2, 3, 4, 5, 6 and 7. If those channels are fuzzy, You definately have a signal issue and need a tech out there to resolve it.
If you are able to, go to you local payment center and swap out the modem, if the problem stops after swapping out the modem, there ya go.
You could also try the following.
Open a command window and run a continues ping to a website then play your game. WHen you experience the latency on the game. Log out and check the ping results and see if it is happening there as well. Not sure if you know how to access a command prompt or run a ping, but my website will help with that. www.shunney.net it will also help with other troubleshooting issues too
New Visitor
Posts: 14
Registered: ‎02-18-2004

Re: What is 64 to 256 QAM?

I ran the diagnostics and found the following results:
DOWNSTREAM
Frequency: 591000000 Hz Locked
Signal to Noise Ratio: 30 dB
QAM: 256
Power Level: -2 dBmV
UPSTREAM
Frequency: 34000000 Hz Ranged
Power Level: 42 dBmV

The item that concerns me is the SNR being 30dB. From what I have read, for QAM 256, the SNR should be 33 dB or higher. Michael, is this accurate? If so, what should I do?
Regular Contributor
Posts: 50
Registered: ‎11-11-2004

Re: What is 64 to 256 QAM?

Your SNR for 256-QAM should be atleast 35 to get a clear signal. You will want to call a tech at 1800-comcast
Most Valued Poster
Posts: 1,408
Registered: ‎10-27-2003

Re: What is 64 to 256 QAM?

This is a list of all modems, that Comcast certifies and decertified on the network: http://faq.comcast.net/faq/answer.jsp?name=17905&cat=Connection&subcategory=Cable%20Modems

So if your modem is one that is certified, then the QAM upgrade is not the cause of your problem.
New Visitor
Posts: 14
Registered: ‎02-18-2004

Re: What is 64 to 256 QAM?

So if my cable modem is on that list (which it is), then having a 30dB SNR is ok with QAM 256?
Or is that SNR bad no matter what QAM I have?