ADSL and Ham Radio
Thu, 28 Oct 1999 12:42:22 -0400
Kevin Muenzler WB5RUE wrote:
> 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.
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