“LIFE, THE UNIVERSE, AND EVERYTHING…” THE FUTURE OF THE RF SPECTRUM Part 1
The recent series of posts dealing, in part, with the future of the Amateur Radio Service launched the Curmudgeon’s thinking into a new direction. Being a “philosopher dude” kind of guy whose thoughts tend to move toward larger and more futuristic issues, the Curmudgeon generalized his thinking to consider the future prospects for the entire RF spectrum! Not that we haven’t touched on this topic a bit already, but rather that it deserves its own special discussion.
In the Curmudgeon’s opinion, the future prospects for the RF spectrum are not good. Of course it’s not the case that the electromagnetic spectrum might someday vanish entirely! Maxwell’s Laws and the constructs of fundamental physics have shown that electromagnetic fields exist even without the ministrations of humans. These fields, which are the physical basis for radio, will still exist long after mankind finishes pounding its collective feet across the surface of the earth.
Rather, it’s our future opportunity to use the electromagnetic spectrum — successfully — to accomplish necessary and useful tasks which appears likely to become sharply restricted. This premise is based upon our current cultural unwillingness to manage and to conserve the spectrum, opting instead to strip mine it for immediate profit (yes, you’ve certainly read that here before!).
So what are the current trends which threaten to bring the diminished usefulness of the spectrum in the future? The Curmudgeon will list five that either now or in the future may play significant roles, but he makes no pretense about being totally inclusive. Indeed, additions to the list are in order, and these would be a very apt use of the Comments function of this blog.
The first trend is the most obvious: over-consumption of the limited available radio spectrum, leading to future spectrum shortages for otherwise useful and necessary new wireless applications. The key question here is, “which new applications absolutely cannot be done without wireless transmission? For everything else, there’s land line.” Or perhaps we just forego making some applications transportable. Negroponte’s Rule summarizes it: “Wireless circuits for mobile receivers, wired circuits for fixed receivers.” And Curmudgeon’s Corollary broadens it: “Not every application absolutely needs to be mobile!”
The second trend is every bit as insidious as the first, but far less obvious: pollution of the spectrum by ever-increasing numbers of (now, mostly digital) radiating electronic devices, leading to ever-increasing noise floors because of greater numbers of random spurious signals. The Curmudgeon can remember the relative spectral purity of fifty years ago. In those days tuning across, for example, the HF band one heard plenty of strong but unidentified signals. However these were purposefully man-made and were being used for some intended job (i.e., long-range radar, broadcast jamming, machine code transmission, etc.). Today the situation is largely reversed: the HF band is filled with low level squawks and squeals, but these are not purposeful. Rather they are the “unintended consequences” of poorly designed digital devices, often located in the immediate vicinity of the receiver itself.
The FCC recognizes two classes of radio emissions devices: intentional and unintentional radiators. Each makes it own, different, contribution to the bedlam on the bands. Intentional radiators are devices whose principal function is indeed to transmit information via emitted EM signals. Often these devices are low-powered and unlicensed. The problem they create is that there are too many of them in operation in many populated areas, creating more and more background RF energy density on the bands which they use. The existing devices make the N + 1st similar device that goes into service just that much less useful and effective. Noise floors increase, useful operational range and circuit reliability decrease, and the general user public becomes disenchanted and begins demanding “more spectrum, more power” etc.
The interference situation with unintentional radiators, devices which were not designed principally to emit RF, today is probably even worse than with the intentional radiators. The principal cause for the increase in problems is the continuing transition from an analog technological world to a digital one. “Digital” circuits inherently create fast transitions between two fixed voltage levels, or, in other words, fast “pulses.” Such pulses can be very rich in harmonics which, if released from a poorly designed device, populate the adjacent RF spectrum with garbage. Additionally when broadband transmission is involved, RF sub-carriers are intentionally produced and these can also be released (via radiation and conduction) from poorly designed devices.
As an example, the Curmudgeon is presently battling a digital “residential gateway” device in his own house, installed by one of the major broadband carriers. Although the box carries a sticker proclaiming, “Tested to comply with FCC Standards” (but which ones?—they are not specified. And did the device pass the FCC emission limits standards), the gateway shrieks RF like a banshee! By examining the specifications for the data transmission protocol used by this model of gateway, and by carefully tuning an HF band radio receiver fed by an outdoor antenna, the Curmudgeon has been able to detect and to verify the presence of some of the various (unfortunately, radiated) RF sub-carrier frequencies which are specified by the standard. The box is, in reality, “digital Swiss cheese!” (And with this device present and operational, one can “kiss the 10 meter Amateur radio band goodbye!”).
For a view of this situation in microcosm, consider the modern automobile. Recalling the Curmudgeon’s observation that “the American public is besotted with consumer electronics,” on-board multiple device proximity is the central problem there. Modern cars are smaller than a generation ago (c.f., the 1976 Lincoln Continental!). At the same time today’s cars routinely carry more electronics than existed in the sum of all the 38 homes on the urban street block on which the Curmudgeon was raised! Physical mounting space is tight, wire bundles are in intimate proximity with each other (thereby facilitating cross-talk), several “intentional radiator” transmitters may be present, and RF shielding and decoupling of chasses and cables has gone the way of the dinosaurs. (Don’t agree? Try driving into a parking garage and transmitting on VHF/UHF with 50 – 100 watts. The proximate car intrusion alarms will serenade you!)
Oh, and no mobile accessory “package” will directly talk to another mobile “package” without an expensive, add-on “converter.” The mess that now exists in cars could be in our homes and offices in a matter of years. It almost takes an interference resolution investigation by LBA to sort out the problems inside some vehicles…..and “more is coming!”
A good portion of the RF pollution problems created by digital devices, in the Curmudgeon’s opinion, lies in the observation that “RF” has become a lost engineering art, one which is practically unknown in the digital design world. Digital designers apparently are largely unaware of the ramifications of their work, potential or actual, on the RF spectrum. Few are exposed to the science of EM fields and the principles of RF while at their engineering colleges; fewer still have practical experience with it as ham operators.
Nominally, of course, the FCC “enforces” radiation and conduction from “computer devices” through its Part 15 Rules. But this established process doesn’t seem to be particularly effective, given that some devices can be “self-certified” and that field enforcement of the existing standards is rather rare! Perhaps the future world will be one where -90 dBm at the antenna terminals of a receiver is the “new” minimum usable signal requirement and where receiver RF amplifiers need exhibit no lower than 3 dB noise figures.
Part 2 of this posting will have more discussion of this topic.
What do you think?
“Let’s keep the universe safe for RF!”
The Old RF Curmudgeon