Free (At Least, Extremely Cheap) Noise! Part 3 Hear No RF Evil - See No RF Evil |  |
| Free (At Least, Extremely Cheap) Noise! Part 3 Posted: 18 Jun 2012 11:18 AM PDT
The Curmudgeon notes that this kind of discussion can only scratch the surface of the problem. Much professional-level work has been done and published in the field, and with a little searching readers can certainly expand their knowledge of all the topics presented here. The principal effect of unwanted RF noise is to raise the "noise floor" for radio receivers located within the noise fields. Practically, this means that the receivers lose "effective sensitivity" That is, they lose the ability to successfully receive some or all of those radio signals that arrive at the receiving antenna with signal strengths about the same order of magnitude as the receiver's inherent thermal noise. Thus the communications channel becomes partially or fully unusable for reception of weaker signals.  Waterfall image of signals and noise in the 80 meter amateur band As an example, a quality VHF receiver which requires only 0.3 microvolts of input signal to produce 12 dB SINAD on the test bench, when connected to a resonant antenna in an urban noise field may require a 5 microvolt received signal at the antenna to produce the same 12 dB SINAD. Faced with this situation, the message sender has two options available for increasing the probability of successful message transmission: raise the transmitter's power output (using one of several different means) or install additional transmitters to provide better and stronger signals over the intended coverage area. [A third option, in the digital domain, is to include Forward Error Correction in the message, but this has other costs and complications.] The net effect is that increased, unwanted noise power begets increased transmitted power as a coping mechanism. Higher transmitted power in turn contributes to increased noise (through unintended signal mixing processes occurring in the environment, including, in some cases, overloading of nearby receivers). And thus the stage is set for a potential "power increase spiral." "Well, so what? What difference does this make for me?" In principle, we can just continue increasing all transmitted power levels and "brute force" our way toward temporary solutions. But this path cannot be more than an interim resolution to the problem; eventually the unwanted noise problem will have to be faced. By analogy, the population will begin to devote serious attention to the problem of air pollution at the time that their automobile engines will no longer combust gasoline effectively in the dirty air. "So, are there costs associated with the increasing levels of radio noise pollution?" Indeed there are, and these are both social and economic costs. What is the cost to our society of the failure to receive a highway patrolman's emergency radio call for an ambulance dispatch to aid victims of a traffic crash? Or of the reception failure of a cellular phone call for help from a hiker after a climbing accident? Or the failure of search aircraft to hear the weak transmitted signals from the Emergency Locator Transmitter on board a downed aircraft? Or failed reception of an "SOS/Mayday" call from a maritime vessel? "Aren't these all just fanciful hypotheses?" Perhaps. But perhaps not. Then there are the economic costs. All that increased transmitted power costs the national economy real dollars. Consider the following "back-of-the-envelope" calculation. Let us assume that there are 1,100 "full power" broadcast television stations in the US. We'll assume that each station produces 50 kW of transmitter RF output power (averaging over both VHF stations, with lower output power, and UHF stations with higher power), that the primary power demand for each transmitting facility is 100 kW, and that on average each station transmits for 18 hours per day. "Doing the math" results in a total instantaneous power demand for the stations of about 100 Megawatts. That's roughly one-tenth of the capacity of a modern "nuke" generating station — just to run television transmitters! The total daily energy demand for the US stations is about 2,000 Megawatt-hours. At an (assumed) "average cost" of ten cents per kilowatt hour (that cost figure may be unrealistic), this is a daily power bill of just short of $200,000, or a yearly cost of $72 million!  10% of a nuclear plant output is needed to power US TV transmitters, alone! "But wait… there's more!" We haven't yet figured in the power usage from broadcast radio, cellular telephone base stations, land mobile dispatch base stations, etc. In aggregate, much more power than given above is being consumed in this country for wireless communications. Now suppose we could eliminate much of the RF noise pollution, especially around metropolitan areas. Suppose we could reduce the noise fields to the point where broadcasters, cellular telephone networks, and other spectrum users could operate successfully with half their present transmitted power levels. That would result in a significant amount of power generation capacity that could be taken off-line and quite a bit of cost savings. Not to mention proportional savings in the costs of thermal, air, and water pollution from power generation, plus additional fuel shipping costs, power station construction and maintenance etc. So pollution does carry costs, both social and economic. The engineering profession is skilled at dealing with matters of economic cost, but the introduction of social costs isn't yet common in engineering discussions. We are used to doing the design and construction work that is needed, at the minimum economic cost to complete it. We don't have much past history and experience in factoring in the social costs of our work, but we are starting to gain some in such areas as the design of automatic electrical (heart) defibrillators and heart pacemakers. The terms "engineering" and "conservation" don't yet fit well into the same sentence, but perhaps in later years they will. There is a basic proposition in play here. We're slowly losing our ability to maintain reliable wireless communications with each other. [Granted, loss of usable radio spectrum is perhaps an even bigger factor here; see "Why is the US strip mining the radio spectrum?" in earlier Curmudgeon posts]. The RF noise pollution factor is insidious: it cannot easily be perceived, and it's difficult for the average citizen to comprehend. But it most certainly does exist and it does increase costs. In the starkest possible terms this question is very similar to all of the other contemporary pollution problems: air, water, land, audible noise, light, chemical, radioactivity, and thermal pollution. For all these sources, the fundamental question is "Are we as a civilization willing to trade off having to live in our own filth solely for short-term economic gains?" It's a fair question, and people of good faith can present cogent arguments on both sides. But it's also a time-limited argument: "Nature is a hanging judge," and in the future rising levels of pollution will force us to act. Eventually we will have to confront RF noise pollution as well. How, then, do we deal with the growing problem of RF pollution? In reality, the answer is the same as with all the other kinds of pollution. And it's a process that we are not yet very good at using. First, we have to quantify the problem. We must measure the magnitude of the noise to understand both the size of the problem and in which geographical areas it is most severe. This will take a much increased supply of cheap, effective radio field strength meters, and a population that is knowledgeable, motivated, comfortable, and confident in using them. Once we have some idea of the "size" of the problem, the additional abatement steps can be planned.  Measuring device RF noise in Fujitsu anechoic chamber In an ideal world, the next logical step would be enforcement. Within the United States, creation of EM noise fields in excess of the FCC's Part 15 Rules is already subject to Commission enforcement actions. But the reality is that, in today's society, effective governmental enforcement is almost impossible. The FCC is not, by any stretch of the imagination, prepared to do this kind of work, unless specific instances of pollution grossly affect "Safety of Life and Property." To replace lack of governmental enforcement, a different mechanism would be effective: economic enforcement. When pollution becomes too expensive, relative to the costs of preventing pollution, the "invisible hand of Adam Smith" will point the way toward solutions. The obvious way "to make it plenty expensive to pollute" is to tax the creation of pollution, either directly or through the establishment of a "pollution credit" trading market. The cost of the taxes or credits is set higher than the costs of pollution avoidance. Even the most rabid "free marketer" will figure out the best course of action under these conditions. But "taxes" are currently not a cherished public policy initiative. It would be difficult, at best, to push into law pollution taxes and especially so because so many different kinds of pollution require attention. A better way, in the Curmudgeon's belief, is to build actual dollar costs of pollution abatement into the price of a product itself. This is not as difficult a concept to implement as might initially be imagined. Some states are now building the costs of the eventual salvage of discarded consumer electronics goods into the selling prices of the new items. Funds are collected at the time of sale and are used to (partially) operate salvage facilities that reclaim materials from discarded electronics items. These facilities need not be governmentally operated; private enterprise can do this job. Similar selling price-based systems exist for the reclamation of used motor vehicle tires. And public understanding and acceptance of this kind of system is generally good. Thus the consumer is both aware of the eventual pollution abatement cost of the item under consideration, and he is also "pre-funding" that cost. And since products compete in the consumer market largely on the basis of their selling prices, those products with the lowest pollution-abatement costs will carry a price advantage.  Noisy e-gadgets – going, going, gone! In this case, the "abatement cost" is the estimated cost that the economy would have to devote either to mitigate the excessive environmental RF noise produced by a device, or to refit the device so that the excessive noise is eliminated at the source. It is not necessarily the separate cost of salvage reclamation at the end of the product's life cycle. Of course it will be more difficult to implement RF pollution abatement than it would be, for example, to implement air pollution abatement, since RF pollution doesn't cause runny noses and stinging eyes. But a population that actively desires a cleaner world in which to live will endorse this process also. And the Curmudgeon would be exceedingly proud and pleased to be present someday, when the last wretched "shrieking banshee" consumer digital box on the earth hits the landfill and blessedly disappears, forever, beneath the tread of a Caterpillar D6! What do you think? "Let's save the universe for RF!" Since 1963, LBA has been providing RF equipment and engineering consulting services for radio and television broadcast and wireless communications.
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