Soaking up the waves. RF might hurt you.
     

I'll never forget one of the first NAB workshops on the hazards of RFR. It was at the 1986 NAB show in Dallas. The venerable Denver consultant Vir James proclaimed, "I've been around RF all my life and can't get enough of it. I love the stuff." Other than a few RF burns over the years, he didn't think his health had been diminished by it one bit. Vir lived to a ripe old age.

In those days, he and many other engineers weren't so sure the newly proposed RFR regulations were completely necessary or appropriate. But the new FCC laws were going on the books designed to protect humans from over-exposure. We all had to understand and abide by them.

The great radiation debate

Debate over the term radio-frequency radiation, or RFR, lingers. That was the FCC's chosen descriptive phrase when the first OST Bulletin #65 was released in 1985. It's not really radiation in the same way most folks understand the term. Ever since Hiroshima, the public associates radiation with the nuclear fission ionizing variety. Radio waves are, of course, non-ionizing, meaning the basic molecular structure of anything subjected to them remains unchanged.

RF energy really is a lower frequency invisible form of sunlight. I'd prefer the term RFE over RFR. It would certainly help to calm down fear-mongering NIMBYs living near existing or proposed antenna towers. In its revised OST 65, released in 1997, the FCC started using the term "radio-frequency electromagnetic fields" in place of RFR. IMHO, RFE is shorter, more appropriate and easier for almost anyone to understand.

The FCC adopted rules regarding RF exposure, based on the National Environmental Policy Act of 1969 (NEPA) that required federal agencies to evaluate the effects of their actions on the human environment. The NCRP, IEEE and ANSI established the limits adopted by the FCC based on specific absorption rates of energy that produce elevated temperatures and possible detrimental biological effects on human tissue.

RF the smoking gun?

Other than this obvious effect of tissue heating, we still don't know what the long-term implications or risks to human health really are regarding absorption of broadcast RF. Like any other abnormal stimulus or agent subjected to the human body, RF exposure may induce different consequences from one human to another.

The rules and guidelines contained in OST 65 really are based on the assumption there might be adverse health risks associated with excessive exposure. The 1997 NAB publication on FCC RF radiation regulation compliance that includes OST 65 clearly states, "Although much scientific research has been done in the area of human exposure to RF radiation, as of this writing no conclusive connection between exposure to relatively low levels of RF radiation and health effects in human beings has been established. ... Neither the FCC nor any other arm of the federal government has determined that broadcast antenna emissions at levels normally encountered by workers or the public pose a present public health hazard. It is important to remember that the regulations have been adopted as preventative and precautionary measures."

It's rather curious the government has gone to such great lengths to protect the public from possible adverse health effects of RF energy but almost nothing in the area of consuming junk food. Ingesting high levels of sugar and fat certainly pose a much larger health risk for everyone. At least they have determined that smoking tobacco is hazardous to one's health and have become rather proactive in controlling its use. But I digress.

Don't get burned

Microwave ovens heat up food really well with a high-power magnetron beam of 2 GHz energy. Certainly human exposure to near-field microwaves can induce problems, especially eye damage if you look right at them. Not much different than watching an eclipse of the sun.

I recall climbing an FM tower back in the 1970s and feeling the heat coming off a 10 kW FM bay within a few feet. Not a very efficient space heater, but I would have absorbed a lot more heat and probable tissue damage by sunbathing on the beach.

If you've talked with any old-timer tower climbers about RF, many will admit to years of probable over-exposure. A few even laugh at the stringent standards that are now law. While most have weathered their past indiscretions with no ill effects, a few have died of cancer and their widows have filed lawsuits. But was RF the real culprit? It's impossible to know for sure.

Reasoning that it's better to be safe than sorry, most responsible tower firms abide by the rules and now require their workers to carry RF sensing devices to warn of hot spots. Sometimes they can be a bit too sensitive. We've heard at least one story of a fussy tower crew delaying work with nervous sensors warning of RF that turned out to be well below safety margins. And then there are a few of those small renegade tower outfits that are willing to ignore safe limits just to get the work done and make the money. Both sides need to be vigilant when working around RF.

Trouble in Caly

Recently, the industry has learned of two RF exposure infractions by broadcasters in California that have achieved high profile by provoking FCC investigations. Thanks to the CGC Communicator (www.bext.com/_CGC) for many of the details we've gleaned on this.

Although various local engineers familiar with the stories also have offered slightly different accounts of what occurred, I believe the following essentially sums up what did happen:

First, the Sunset Ridge incident involves a TV station that allegedly turned up its transmitter power to full throttle when tower workers were on the tower in proximity of the antenna. Apparently an out-of-state TV network director of engineering ordered the local station to resume full-power operations. It is not known for certain if that individual realized there were tower workers being exposed to high RF energy by his decision.

Whether the workers were exposed to dangerous RF levels is unknown. Personal RF monitors worn by the workers alerted them. Apparently, they were able to climb out of the hot area before the transmitter was again shut down or before time-averaged extended exposure was exceeded. The FCC is investigating and may issue citations to the local station. Heads could roll on this one.

Miscalculation gone awry

The other incident involves a TV station installing a new DTV antenna on Mt. Wilson. This site is perhaps the busiest and largest antenna farm in the nation and is home for most L.A.-area FM and TV station transmission facilities. Getting all nearby stations to co-operate with necessary power reductions to allow such work is understandably difficult and time consuming.

The TV CE notified and secured the co-operation of all nearby stations he calculated would present a problem for tower workers doing the work. But RF safety monitors started beeping as workers climbed the tower. He apparently had forgotten the RF contribution by a nearby FM station. The CE of that station was called, with no prior notice, and was asked to reduce power by 20 percent so the work could proceed. He complied and work progressed without further incident that day.

The next day, the FM station was again asked to reduce power. This time their corporate engineer initially declined to co-operate, apparently citing loss of coverage during morning drive and inadequate advance notice for non-emergency work that should have been pre-scheduled outside of drive time. The TV CE understandably was not happy, with an expensive tower crew waiting to go to work and all other stations onboard.

A big can of worms

After a few hours of heated discussions and delays, including having to persuade the station's management that a power reduction of only 20 percent would not affect meaningful coverage, the FM station did lower power and work proceeded. However the local FCC field office was made aware of these proceedings, spilling a can of worms all over Mt. Wilson. For the next several days, a cadre of FCC officials visited the site to do a thorough inspection and RF compliance evaluation.

All of the stations involved in the vicinity of the DTV project were required to shut down transmissions one by one for brief periods to allow for actual RF density measurements. Perhaps the most obvious infraction was an access gate left open and unlocked that essentially allowed public access to the area. The reluctant FM station may not have violated any actual rule. Those responsible for leaving the gate open and unlocked probably did.

There are hundreds of mountaintop FM and TV tower sites all over the country. The FCC recognizes the public does not normally frequent them. But just like sites in populated neighborhoods, the main thing that prevents easy public access is an effective locked gate at the access road and a perimeter fence if feasible. Warning signs also are necessary but are not enough by themselves.

Setting the example

A number of Mount Wilson station CEs expect that some citations and possible fines will be issued. As of this writing, the FCC still is analyzing its measured data and the facts involving the incident. The commission apparently wants to set an example and raise awareness with this episode and sees RF compliance as a hot-button issue, along with EAS.

The FCC's rules on RF exposure and compliance have been on the books for 18 years. Every station must certify that its antenna installation complies with the rules at license renewal time, including provisions for power reduction to protect workers. Multi-user sites have had to cooperate on a mutual basis to ensure that tower workers as well as the public are protected from any over-exposure.

Most such sites have drafted written procedures that spell out how much power reduction is required for workers to safely access mapped areas of the tower structure to perform work or maintenance. Mt. Wilson users now are carefully reviewing their plan and likely will update it to cover any contingency.

Certainly reliable communications need to be established and maintained between tower crews in the air and engineers on the ground when tower work is underway. Now that personal RF monitors are widely available and in use, there should be little chance or reason any tower worker is over-exposed to high levels of RF. Every CE employing tower workers on his site should insist on their use. This is just good inexpensive insurance.

The keys to preventing problems in this arena are careful planning and execution, with everyone involved paying close attention to established rules, procedures and common sense.

Can't we all just get along?

It would appear that the Mt. Wilson boondoggle could have been prevented and kept off the FCC's radar screen had a little more mutual understanding and co-operative spirit been employed. Scheduling non-emergency tower work during morning drive in a major market is usually never done unless there are special extenuating circumstances. Coordinating with those stations involved with as much advance notice as possible for non-emergency work is common courtesy.

On the other hand, a request to reduce power by only 20 percent is almost no reduction at all - a little over 1 dB in lost field strength. Usually, such reductions are 50 or even 90 percent. When work is underway, with men on the tower and other stations running at reduced power, common sense dictates that co-operating to get the job done would have been the wiser choice, one that also would pay off in the future. Every station that is part of an antenna farm complex eventually will need to deal with its own problems or projects that require the co-operation of its neighbors.

When you need a favor, everybody remembers who cooperated last time and who didn't. Of all the rules we might want to impose on tower work operations, perhaps the golden rule is the one that matters the most.

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Comment List:

Your statements are debatable - like the first one that It took until the mid 1990s for an AM/FM radio to become standard in cars. That's just pure crap and if you believe it you're a bigger fool then most. The issue here is that none of those technologies you mention displaced, obsolete, trash whatever you want to call it, any existing technology like digital radio does. They were just additions to a wide array of consumers choices. I wish you people would stop making those comparisons. If it takes losing the war to win the battle then I will have won the war. Do you work for iBiquity? - tell the truth now.
By Radio Engineeer on 1/5/2010

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