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. 

Here is a quote from http://www.orckit.com/fr_newsa.html?/qam.html (Orckit manufacturers VDSL equipment) illustrating that VDSL proponents are well aware of the HF interference problem:

"The high spectral bandwidth utilized by VDSL transmission systems presents another major performance criteria, in addition to the obvious reach/noise margin one. The VDSL signal spectrum overlaps with the HF band which may cause high levels of narrow-band interferences. Standard DMT systems may suffer significant degradation in performance under such strong narrow-band RFI signals. It is definitely possible to improve DMT's narrow-band noise immunity, but, at VDSL data rates, the implementation complexity incurred is significant. Moreover, many of the proposed solutions are limited to a pre-defined set of frequency bands, thus not providing full coverage and RFI protection. In QAM systems, high level of narrow-band noise immunity can be achieved at relatively low complexity. The main reason for that is the inherent capability of single-carrier receivers (based on adaptive equalization) to reject and "notch out" narrow-band signals."

If, and it’s 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, maybe 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 … 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.