[RFI] RFI U-verse

[Charles Coldwell]

On Feb 27, 2011, at 6:31 PM, Martin Ewing wrote:

> AT&T's U-Verse service is based on VDSL2, which uses frequencies from around
> 100 kHz up to 8.4 MHz in carrier channels of about 4.3 kHz bandwidth.
> Typical phone lines at typical distances limit the maximum usable frequency
> because of excess attenuation.  My line, about 2100 ft from the U-Verse
> fiber node, won't carry channels above about 5.7 MHz. (More at
> http://aa6e.net/wiki/Uverse )

I have Verizon FiOS to my home, so they terminate an optical fiber in my basement on a big white box they call an ONT (Optical Network Terminal, essentially the telco demarc) from whence both CATV (QAM?) and WAN/Internet emerge on one 75-ohm coax cable.

By default(*), residential FiOS is configured with the WAN/Internet carried in a high frequency band on the same 75-ohm coax that carries the digital cable signal (QAM?) to the set-top box (they call this MoCA or "Multimedia over Coax Alliance" -- it vaguely reminds me of the old 10-Base-2 ethernet on 50-ohm coax).  The coax emerging from the ONT is divided by a 3dB splitter, with one leg going to the set-top box and the other to the home router (Actiontec MI424-WR).  The router NATs the Internet connection to provide a LAN on yet another frequency band on the coax as well as four standard twisted-pair ethernet jacks.

So the 75-ohm coax in my home carries two IP networks (LAN and WAN) as well as the CATV signals.  The STB is a host on the LAN, and both video on demand and the program guide are delivered to it over the IP network.  I also have a small MoCA-to-twisted-pair adapter near the television that lets me put my over-the-top box (Roku) on the wired network to avoid clogging the ISM bands with streaming video.

From an RFI perspective, this arrangement seems very robust.  Obviously, the signals coming into my home on optical fiber generate no RFI.  The ONT is well grounded and shielded and quiet as a mouse on every band I've tested.  The long runs from the ONT to the STB and router are in shielded coax; the only unshielded runs are relatively short CAT5 twisted pair runs from the router to a couple of computers in the same room.

Does anyone have the U-verse fiber-to-the-home service?  Is their architecture similar to Verizon FiOS?

73 de W1CMC

(*) Commercial installations usually use a standard twisted-pair ethernet jack located on the same ONT.  Residential installations can request to use the twisted-pair jack, but since the STB relies on IP/MoCA for video on demand and the program guide, those services will be lost.

--
Charles M. Coldwell, W1CMC
"Turn on, log in, tune out"
Belmont, Massachusetts, New England (FN42jj)

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