[Date Prev][Date Next][Thread Prev][Thread Next] - [Date Index][Thread Index][Author Index]

Sorry for the SPAM but this is pretty important stuff....

Information to consider.
73 Kevin, WB5RUE

Home Networking, VDSL and HF Radio Interference

HF Amateur Bands Just Became Shared With High Speed Data Services

                                    Ed Mitchell, KF7VY,

Ham Radio Online was the first to document the interference problems with
the new "Home Phone Networking" technology. Home Phone Networking, also
known as HomePNA (from the industry group that is developing standards -
Home Phone Networking Association), modulates computer data signals over
existing home telephone wiring. Using existing HomePNA technology, you can
create a 1 Mbps computer network inside your home using your existing
telephone wiring. The 1 Mbps technology works by modulating data signals at
5.5 to 9.5 Mhz - and is literally transmitting an HF radio signal, using the
phone wires as a transmission line. Those of us who have experimented with
HomePNA technology have found that it is capable of generating significant
HF radio interference, and is also highly susceptible to nearby, low power
Amateur radio transmissions.

In an only a few months time, the HomePNA technology has exploded onto the
home networking scene. Market researchers believe that HomePNA will rapidly
reach 50 to 70% marketshare. Depending upon the demographics of where you
live, you may soon find yourself competing with a home phone line network
for access to 40 meters.

During the summer, the HomePNA announced they had agreed on a preliminary
draft of a new 10 Mbps home phone line network technology. Diamond
Multimedia has jumped the gun in advance of the final specification, and is
now shipping the 10 Mbps technology. Because details of the 10 Mbps
technology are not yet public, we do not know which HF frequencies are used
by the new technology. Indications are that the new 10 Mbps systems are
based on VDSL. There are plans to eventually increase the HomePNA network
technology to speeds of 30 Mbps or faster by using the entire HF radio
spectrum up to 30 Mhz.

VDSL is another of the "DSL" technologies that telephone companies are using
to deliver high speed data services over existing copper phone lines. You
may already have heard of "ADSL", which is the type of DSL presently being
deployed by phone companies for fast Internet service. VDSL can provide up
to 52 Mbps transmission speeds, and operates by modulating its signals over
the entire HF radio spectrum.

The VDSL proponents are well aware that VDSL generates significant amounts
of HF radio interference, and that it is also susceptible to outside RF
interference. The basic VDSL technology puts a signal onto unshielded copper
phone lines running down your street, at a level of -60 dBm/Hz. Because they
are aware that this level will cause interference to HF Amateur radio
operation (an open admission that VDSL destroys HF radio), they have placed
in the specification for VDSL, the option for service providers to add 20 db
of attenuation in the HF Amateur band allocations. This places the signal
level, within the Amateur bands at -80 dBm/Hz. However, they are knowingly
planning to do nothing about the rest of the HF spectrum, causing severe
noise problems for short-wave listeners. If widely deployed, VDSL will mark
the end of shortwave broadcasting and listening here in the U.S.

If, and itís a big IF, a service provider elects to implement the
optional -80 dBm/Hz signaling in the Amateur bands, this, in theory, reduces
the noise to a level where it will almost fade into the noise level at 35
feet from a phone line carrying the VDSL signal. In theory. The tests that
were conducted used a perfectly balanced short phone line segment (see
research papers at the VDSL forum at http://www.vdsl.org) and matching
baluns on the 20 meter dipole used for the tests. In real life, once the
VDSL signal leaves the pole and traverse into your house, the quality of the
wire installation is a random unknown. Based on experience with HomePNA 1.0
phone line networks, and their problems on real-life residential in-home
phone wiring, it is highly likely that VDSL signaling will emit far more
noise than laboratory tests suggest.

Deployments of VDSL

Phone companies are anxious to finalize and deploy VDSL since it would
enable them to compete equally with cable TV systems. I won't go through all
the technical details, but it would enable them to deliver digital video
signals to the home. Currently, cable TV systems are making rapid plans to
add phone service to their cable TV systems.  So you can see, phone
companies have significant incentives to get VDSL working soon. In some
locations across the U.S., local telephone companies are now selling and
providing VDSL services.

Watch for the "DSL" technologies to be pushed aggressively over the next few
years. The phone companies' futures are riding on their ability to make
these technologies work.

HF Radio Just Became a Shared Band

Home phone line networking and VDSL technology are significantly different
than other forms of HF noise. This is not pulse type power line noise that
can be eliminated with a noise blanker. The interference is caused by the
simple fact that these new technologies are true HF radio transmitters and
receivers. In effect, the Amateur allocations (and all of HF) have just
become a shared allocation. HF Amateur radio will now share its HF bands
with your neighbor's high speed internet access and home computer network.
Amateur transmissions will also pose a challenge as they will have the
potential for disrupting these HF-based signaling systems.

This is a critical issue to which most Amateurs have not given any thought.
Perhaps it won't matter. As noted in a previous column, the Amateur service
just became a VHF/UHF centric radio service anyway, and HF radio operation
amongst U.S. Amateurs is declining.

But its important for all of you to realize what is going on here - HF radio
won't be the same ever again. The noise level at HF will increase
dramatically. If you are lucky, aybe your neighbors won't use these new
technologies for a few years yet. But when the FCC is faced with the choice
of preserving narrow segments of HF for Amateur telegraphic operations,
versus providing high speed Internet services to homes, their decision will
be easy. Don't look for salvation in regulations.

Some of us are frustrated by all this Ö and I don't mean by the new
technologies that will pollute HF. Our frustration is from the apparent lack
of interest by the Amateur community. As a result, HF radio use by any
suburban or urban dweller really is dying.

Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org