DARK BANDS?

he speed of dark! That may be answered soon in the USA if the FCC approves the widespread implementation of BPL (broadband over power lines) as some bands of HF operation just may go dark and be wiped out from the noisy interference expected by many experts. Will yours be one of them?

Even if not wiped out entirely, many other bands may likely be affected to some extent by the interference expected. I say, “may” as some of those experts are busy researching the issue and making efforts to establish hard evidence as to what will really happen. Further, we can look at other countries that have already implemented power line communications. Of course, some bury their power lines and the problem is not as great in that area.

Am I overstating the issue? Maybe, but the evidence of problems ahead for HF operations and perhaps other forms of communication appear at risk of becoming victims to some extent or—worse, completely unusable. But, I doubt if much of the general public has ever heard of the BPL project, however may wonder later why there is more interference on their TVs—or hum on their AM stations, or…….???

Take for instance one bit of research discussed in a thread about this issue on the antenna-discussion list (names not disclosed here):

From: Not disclosed here
Date: Fri, 26 Mar 2004 03:16:26
Subject: [Antenna Discussion] Purchased a pair of Belkin BPL modems for testing

Has any ham actually bought a pair of in house BPL modems and tried to operate them while looking for ham band interference???

I am interested in hear your experience (especially if you are in the emc compliance business, I am. Most of our products should be immune but none have been tested.) I heard about the BPL discussions from a comment on the IEEE EMC list server.

Professionally, and as a ham I am deeply concerned about the roll out of these products. I have since purchased a pair of Belkin in-house BPL modems, (www.belkin.com) a power line 10baseT Ethernet model F5D4070 and power line USB model F5D4050.

My ham station is modest, most of my antennas are inverted V's. My 1954 house is wired with armored BX wiring except for a length of romex cable powering the whole hamshack.

Initial impressions of these 2 particular samples are as follows.

1) Cannot turn off the encryption, thus the throughput is best at approximately half of my alternate 10baseT drop, yes!!!
2) Have NEVER seen any ham band interference from any of my multiple 10baseT drops in my house. This particular CAT cable is unshielded.
3) I can barely see any interference on 20 meter PSK at night when band is closed down but I can see some agc action during quiet to bursty transfers.
4) Interference is heard on 30 meters, 10 MHz WWV is clobbered!
5) Noises are heard on 40 meters, need to look further.
6) New 5 MHz frequencies are clobbered and so is 5 MHz WWV.
7) Have not checked 80 meters or 15 meters.
8) Hanging a 2-foot cliplead off of my HP 8569B spectrum analyzer I can easily see the BPL emissions and the notches. Displaying the BPL emissions works best on max hold. The frequency span of these modems appear to be approximately 4 to 21 MHz.
9) Belkin claims compliance to FCC Class B but I don't a good feeling about this. (Unintentional radiator my ..ss!)
10) When my wife runs her sewing machine that disrupts it's data flow.
11) Been trying to come up with a method to attenuate the line output of one of the devices to dynamically force it for max power output and frequency spread.
12) I have NOT had the time to measure conducted emissions nor has our OATS site been open for me to sneak in on a Sunday and takes some emission scans. [...]

In response:
[...]Please keep us all posted as your observations come in. Are the devices you are testing HomePlug certified? That is a fairly significant difference between HomePlug equipment and the typical BPL box, but the experience is instructive, nonetheless. HomePlug actually cooperated with the ARRL in making some design changes that minimized the QRM. After your reports, I wonder how bad it would have been without that?[...]

In response:
[...]Yes, as said, the in-home units were very bad, but HomePlug worked with the ARRL to quickly "notch out" the HF hambands. I don't know if these have the same performance as the HomePlug units. The interference on 10 MHz WWV is indicative of how bad things could be on the hambands without "notches". It is also true that access BPL on power poles might be much worse.

The CAT 5 cable is a bunch of balanced pairs, two-wire transmission lines like twin-lead. It doesn't leak much either. It is balanced and usually properly terminated, with little common-mode radiating currents. I have 10BaseT here and don't notice it much either.

But power lines, unbalanced with many open "half-stubs", could be much worse of a "leaker". Providing protection for the hambands doesn't fix interference problems on other frequencies.[...]

In response:
As a seasoned veteran in EMC design of PCs, networking, and telecommunications products, I have a few comments to make on this subject.

First, about the particular unit mentioned...

re: the real source of 10MHz:
As for the 10MHz, one is likely to get that as the oscillator used for 10BaseT PHYs (20 MHz) and you can expect that it'll at least divide that down by two (10MHz, and four, 5MHz) in the circuit. When I used to do a lot of designs like these, this was a pretty common. But most 10BaseT stuff today is tame compared to what things are like with 100BaseT where the first cutoff is at 125 MHz (due to the encoding). The chipmakers have gotten a lot better at designing these PHYs and the GigE stuff is essentially got the same overall energy bandwidth as 100BaseT as it is just encoded differently with more pairs active. So be careful assuming that 10MHz is from the BPL stuff. I wouldn't doubt that it is but it could just as well be a poorly done 10BaseT circuit generating common mode signals in spite of the twisted pair interface. The typical clamp-on ferrite chokes won't be of much help down there as they are more effective at higher frequencies.

re: BPL in general...
It would seem that while communications on power lines is possible, doing so
in an RF silent manner is not possible. What can happen at power line frequencies is much different than that at HF and higher as most of us know all too well.

Just about every principle I use to quiet an electronic product (even to "stealth" levels) is violated in this type of signaling arrangement. There a lot of tricks the BPL folks will have to use to keep levels down but from what I gather its a whole lot like DSL would be if it were broadcast over antennas. If you don't know what that'd be like, I can tell you that you wouldn't like it.

So "filtering and bandpass control is the only alternative" it seems... at both ends. At the device and at our receivers. What a bad deal...

And what about in the long term? Profit motives will reduce the interest in preventing interference to nil. Don't believe this? How quiet is your PC? Did you know that a properly designed PC is quiet enough to run a short-wave receiver with a whip antenna next to it and get some useful listening done? I haven't seen many of those these days and EMC test houses are always on the lookout for really quiet machines to use and they are rare.

So do we think that we'll fair better with BPL?

So what about that company working with the ARRL? Any person reasonably skilled can make one unit work especially for one particular situation. It's a whole different matter when you manufacture hundreds of thousands of units a month.... and ship them to just as many different situations. Do you think that they'll stay as quiet as the one was "made to be" at the ARRL? I don't.

What most folks don't realize that meeting FCC emissions regulations only requires the manufacturer to prove that ONE unit did pass (sometimes at a fractional dB of margin) at ONE time during a particular test. Not every unit that ships passes... surprised? Also, profit motive makes the suppression solutions rather flimsy and unreliable. What happens with time? So how will each of us fair? Will we get a barely quiet one or one of the typically noisy units?

Perhaps I sound cynical but I've been in many those corporate meetings when the product development folks and management make their decisions. When the decision comes between dollars or interference, I have no doubt which way it will go. I also know what they'll want us to believe about it. The marketing hype will tell you the story... just wait...

Folks, I like fast internet but not at this price. Fight this one... especially if you like amateur radio.... this is a product we can do without. [...]

But....?
One of the major U.S. national newspapers recently printed a article on this subject too. Basically it said: "radio amateurs are old-fashioned people who are using 50-year old technology and anyone who is modern will not listen to such out of date people. Rather any really modern person will be overjoyed to have BPL." Oh-oh! Not a nice way to put it! Mars anyone? Pilgrims, hitch up those wagons!

How likely is this new form of PLC to become a reality in the USA? For starters, President Bush spoke recently about the benefits of more broadband, although not specifically BPL/PLC. The President is backing broadband expansion because more competition drives down the cost so more people can afford it. Then more people can communicate better and faster to help commerce to grow. With the President in favor of more broadband, will likely give more impetus to the FCC to approve BPL.

Some think this is "political"....but, what isn't political in some manner? Although I don't profess to be any sort of expert in political science, some definitions state the following, which is close:

I say it is commercial and if you turn your hat around, it's obvious. Setting up the initial distribution is an enormous cost for any new company entering the market because they are without an Infrastructure. But, the power companies can enter the competition with very little more investment. They already have the wires leading to EVERY customer within their market—and the cable company market—and the phone company's DSL market. Plus, these power companies have "powers" in more than one way—they have lots of capital and can launch huge advertising campaigns to sell this new product. If other forms of broadband companies are any guide, that campaign will brag about how much faster this new product is and how much quicker their staff will handle your needs, thus confusing and selling, selling. selling.

Listen to those ads we already have. Most of them won't tell you precisely how fast their transmission speeds really are—just that "their's" is faster than the "other guys." In the long run, the good old "test of time" will sort this out if a customer is lucky enough to have a choice. Those that don't have a choice of course will applaud the new product allowing them to finally get better speeds. Read Levente Letso's article comparing the various broadband delivery systems and it will become clearer as to what is really possible on these systems.

THE CLOCK IS TICKING
The NPRM on BPL has been published in the Federal Register. That means the clock starts ticking on the 45-day comment period. The PDF version of the NPRM is 38 pages, and is available at:
http://hraunfoss.fcc.gov/edocs_public/attachmatch/FCC-04-29A1.pdf

If you have concerns about this issue, you are urged to visit the above document to see what is proposed and what those who are in support or opposition have to say about the approval of BPL. Over 5,000 have already filed comments.

Earlier, antenneX circulated a draft of a document authored by Tom Cox in opposition to BPL to our announcement list of thousands. Many of you offered suggestions and we thank you for taking the time to do so. Tom has since filed the document and advised us how to find it as well as the many others. You are urged to post your own comments before the “horse is out of the barn.” Now here’s how to visit this issue at the FCC website:

From: Tom Cox
To: antenna-discussion@antennex.com

QST, Listers,
The comments PDF under my name is now up on the FCC's sites for both dockets -- 03-104, and 40-37.

To review the posts, as before, follow these steps:

1) Browse to the following page: http://www.fcc.gov/cgb/ecfs/

2) Move the cursor over to the right margin, and click on the "Search for Filed Comments" link.

3) A search form appears on screen. If you want to browse all filed comments, just put either 03-104 or 04-37 in the "Proceeding" field (Field #1). and click on the "Retrieve document list" button at the bottom of the search form.

4) To see my comments only, just put the following in the "Filed on behalf of" field (Field #5):
Thomas D. Cox, KT9OM

I encourage you to read as many comments as you have time for. Many are excellent, and show a great deal of thought. Others, well...

I also encourage everyone (again!) to compose comments of your own, and post them to the 04-37 list. We need to nail the FCC to the wall on the mechanism for regulating BPL. If we persuade the Commission to regulate BPL in a responsible, technically sound way, it won't get very far before it can be overtaken by any of a number of smarter approaches to broadband Internet access that are already out there, or on the horizon.

For the process of posting comments, I refer you again to the ARRL article at:
http://www.remote.arrl.org/news/stories/2004/03/18/100/?nc=1

I also welcome the opportunity to review and comment on your comments in draft form, as so many helpful people did for me. Remember, the comments deadline is May 3rd. Tick, tick, tick!
73, Tom, KT9OM

To help further our education on broadband in general and more about BPL/PLC, Levente Letso has authored an interesting article this month, entitled “BPL: Perspective and Commentary.” His article is accompanied with a companion article provided through Levente as a courtesy of CQDL Mannheim Stoerungs of their February 2004 issue article entitled “Interferences instead of shortwave broadcast” by Dipl.- Ing. Ulfried Ueberschar, DJ6AN Dipl.- Phys. Thilo Kootz, DL9KCE. English translation by Karl Cornelius. Our thanks for the publication’s permission to use this article.

Should this "interference" occur as a result of BPL, it may alter drastically the way we operate. If so, in addition to being concerned about the implementation of BPL, shouldn't we also be thinking about the future of that issue in terms of how we will operate, especially for the bands most affected — or even wiped out? How will we do it?

Meanwhile, back at the equipment store. This issue has been in the works for a long time, but only just now is reaching the brink of implementation. There is a very good chance it will be approved. The modem/equipment companies believe so too and are already manufacturing and selling products for it. Here is another bit of information about the manufacturing activities from our discussion list:

Rather than rambling on and on here about this subject, the above will give you plenty to digest and think about, plus more reading is available in the many threads posted in the antenna-discussion list. If you haven’t joined this list, you are encouraged to do so to help stay current on this issue plus a wide spectrum of other antenna-radio-related subjects.

AN INVITATION TO CONTRIBUTORS
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antenneX thrives on the contributions of antenna experimenters, ranging from the informal home shop construction project to the theoretical investigation of basic antenna, feedline, and propagation phenomena. Over the years, we have published articles on the use of new or newly adapted materials, known antennas adapted to new circumstances, modifications of antenna structures, basic explorations of both common and unusual antennas, antenna modeling exercises, design improvements, antenna matching techniques from both a physical and mathematical perspective, evaluations of mini-antennas and their underlying theory of operation, new and patentable designs, propagation tutorials, and.... The list goes on, since no antenna-related topic is irrelevant to the readers of antenneX.

At the same time, antenneX has experienced continuous growth in its readership—for which we are appreciative. However, all readers can help us do even better. How? By submitting an article every now and then based on your current antenna work that may be useful at any level to other readers.

Among the engineering and researching readers, there are undoubtedly a number of unclassified and non-proprietary findings that antenneX readers would like to know. Among the practical antenna designers, there are ideas, tests, and numerous other practical findings to benefit our readers. Antenna builders very likely have some techniques to share with other readers. Besides the regular articles, we always have the home work shop column for shorter practical ideas and we always have the invited news and editorial column for information about new technologies, future advances, lost old but good ideas, and personal views on the good to bad things that are happening in the world of antennas and propagation.

If you are uncertain about whether your ideas merit an article, please feel free to send an outline to the general editor/publishers at submissions@antennex.com . Do not feel that you must be ready to be a regular submitter to write for antenneX, because we welcome the individual contribution as much as monthly articles. As well, do not believe that the slots in each issue are already spoken for—we shall always make room for a worthy article.

Circling the Square Quad
By L.B. Cebik, W4RNL

A question posed to LB every now and then is whether the circumference of a circular quad loop and the circumference of a square quad loop--both with the same diameter wire and the same resonant frequency--are the same. It is an interesting question, since without any analysis, it seems to have a simple answer. However, like most questions of its type, it hides numerous complexities, some related to the motivation for the question, others related to the variables involved in developing some kind of reliable answer.

Lab Notes: An SWR Bridge
with Automatic Level Control
By Joel C. Hungerford, KB1EGI

Last month Joel described the issues associated with providing an automatic level control for an analog SWR bridge. This month Joel built and measured the parameters of the voltage variable attenuator and the emitter follower output stage that drives the SWR bridge.

The Off-Center-Fed Antenna
& a Design Result for All-Band Use
By Fred M. Griffee, N4FG (EE Retired)

The history and articles of the popular Windom and Off-Center-Fed (OCF) resulted in Fred's particular model design using NEC-Win Plus. After reviewing countless references, discussions, arguments, and recommendations, he decided to design an OCF antenna but use 450 Ohm (really Zo is closer to 400 Ohms) all the way to the shack. This approach results in much lower loss and higher efficiency that can be experienced by using a balun and coaxial cable for the transmission line run to the shack.

Improving Magnetic Loop Performance
By Claudio Re, I1RFQ

Recently, on the antenneX discussion list, several contributors expressed interest in learning more about improving the performance of compact loops. This was prompted, in part, by the introduction of some new antenna concepts based on recent articles on the “Cubes Family.” Those articles by Dan Handelsman, and Claudio are now in Archive VI of antenneX — a discussion of the evolution that Loop designs have taken toward efforts to improve performance over the Magnetic Loop.

The most common question seems to be this: “What techniques are available to significantly improve the performance of loops?” Over the last few years, Claudio has spent quite a lot of time reviewing this subject from the point of view of the ham radio operator. This article contains some of the useful results of these studies.

Innovative Magnetic Loop Remote Tuning
Motorless, Vacuum Capacitorless, Yet Remotely Tuned
By Anselmo Stiffan, IZ3BGJ

Anselmo's objective here is to demonstrate how remote tuning is possible without the complexity of expensive moving parts on the antenna. The prototype is fully operational but the extensive usage of adhesive tape to hold the parts together is not making it a durable product. The article relies on the dexterity and creativity of the reader who wants to build a serious and professional-like version, granting a performance result worth a small investment in time and materials.

FINALLY! THE SMITH CHART DE-MYSTIFIED!
A Demoware Review
by WA5SWD, Ed Lawrence

Would the Smith Chart be used more if it were not so difficult to understand and use? Ed thinks so now that he has found some unique Smith Chart software that makes it much easier to produce the results this technique and tool was intended for. Ed describes the program's use and provides a source for a free download demo version for trial.

Well, there you have it, folks—thanks for listening and remember, the reading lamp is always on for you in the reading rooms. If I can be of further help, I'm just a Stone's Throw! away. April 2004 antenneX Online Issue #84
reGARDS, Jack L. Stone, Publisher jack@antennex.com