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Sherlock Ohms

The Case of the RF Disturbances

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OLD_CURMUDGEON
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Platinum
RF DISTURBANCES!
OLD_CURMUDGEON   11/28/2011 12:53:46 PM
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Two thoughts regarding this blog.

#1)  While designing HF & VHF transmitters in the 1960s & 1970s, a common practice to test the chassis for "hot spots" was to Scotch tape an NE-2H neon bulb to a long piece of tuning coil core stock and with the transmitter energized, move the bulb all around the chassis, not only in the immediate vicinity of the transmitting tube(s), but also in the "tank" circuit section.  RF hot spots would make the bulb glow brightly.  That was an indication of spurious & degenerative power in the equipment.  Depending on the operating frequency range, designed power output, and other factors, a sheetmetal redesign may have been warranted.

#2)  At the early stages of WW II, my father was in the U.S. Navy.  His "MOS" was Aircraft Technician I, however his REAL "job" was to service & maintain the then top-secret RADAR facilities in support of the operations headquartered in Morocco.  He was detached to a squadron of PB-Y aircraft, station in nearby Rabat.  He died of pancreatic cancer @ age 59.  I have often pondered WHY?  His lifestyle was fairly exemplary in his daily routine.  He was NEVER sick w/ any of the common contagious diseases that plague so many, especially during the winter months.  He had NO physical ailments, and never needed to see a doctor, UNTIL he started to complain of back pain in August of the year he died.  By November, he had been confirmed diagnosed, and was dead by Jan of the following year.  In the early 1940s, RADAR waves were not as explicitly understood as they are now.  Was his daily exposure to this radiation somehow a cause of terminal illness?  I'm NOT a doctor, nor a research scientist.  I just ponder this anomaly twice a year, on the anniversary of his birth & death!

bdcst
User Rank
Platinum
Re: Just Bzzt on the stereo?
bdcst   11/28/2011 1:01:49 PM
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Actually the age of digital modulation will make it much more difficult for the general public to detect or understand RFI.  Digital with good error correction will work through some interference sufficient to make an analog signal annoyingly noisy.  But at some point it will simply mute, poof!  There will be no tell tale sound of the interference generator be it a fish tank heater or nearby radar antenna.  Most folks will never know why their on the air (OTA) DTV reception is so unreliable and will simply give up.

Anicodally, I once got a call from an airport whose FAA C-band satellite receive dish was having sporadic interference.  I suggested they add a flange mounted C-band bandpass filter similar to what I was using at a nearby public radio station to eliminate desense from the airport's own radar and aircraft altimeters.

Digital reception is not going to make the public more aware of RFI.  On the contrary, it is interference from digital devices that makes analog modulation less and less useful!  Listening range of AM radio has been severely diminished by the rising RF noise floor everywhere.  And lets not forget the BPL fiasco, broadband Internet over unshielded power lines!  Those of us whose amateur radio hobby is still mostly analog can attest at the threat of BPL, a solution looking for a problem and creating its own havoc along the way.  Is the dollar mightier than the physics textbook?  You cannot rewrite the laws of physics.  But it seems you can buy your way around the laws of regulation.

APG3 inventer
User Rank
Iron
It can toast you and you can toast back!
APG3 inventer   11/28/2011 1:34:30 PM
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Like another responder, I was on a military base in the south Pacific.  The large - I mean large radars being developed - had a grounded screen around it.  A tall fence that would shield the island from the radiation.  After use, dead birds and such were cleaned up between the building and the fence.  Microwaved on the fence or in the air.  - Navy guys often talk about working on this or that antenna and getting warm.  A tracker ship with 100' dishes on it cut doors in half as some were resonant.

Now for the "take back the skies" thought - I was flying a 2-M sail plane on the West Coast - and we would start loosing control of our wings in an area.  The gas guys flew bi-planes and single wings - and often had the same issue.  Then one day a guy drove out to our area - an old runway in the weeds - he was the IT manager of a graphics company - his Earth station (ftp over a satellite link) was dropping out when we flew in a region of his beam.  We moved (sad for us) to a high school with permission - and wished the company would relocate, but never did.

 

bdcst
User Rank
Platinum
Re: RF disturbances more scary then an nuisance?
bdcst   11/28/2011 2:08:02 PM
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I don't think you can say amateur radio operators are among the healthiest folks, not without a scientific epidemiology study.  I've known hams who died from brain cancer and hams who are indeed in their 80's and are still on the air.

The FCC imposes fairly stringent exposure regulations on licensed commercial emitters of RF energy, broadcasters.  License applications have to address how a facility prevents over exposure to the general public and to workers who might find themselves near radiating antennas on rooftops or towers.  Radio Amateurs have to self certify that they've read the RF exposure rules and their ham stations are in compliance.  My guess is many hams probably are not in compliance.

Cancer triggers are hard to pin down as so much of the biological response is governed by the genetic roulette wheel.  Some folks, like my brother-in-law and his grandfather, chain smoke their entire lives and never acquire lung cancer while mere second hand smoke can be fatal to others.  You also have to follow people for many years, maybe decades, as the carcinogenic affects can take a long time to manifest.  Animal studies using mammals other than humans, for obvious ethical reasons, may not reliably model the human body's response except, maybe for thermal damage to corneas as in the rabbit studies previously mentioned.

SAR (specific absorption rate) depends upon RF wavelength, distance from the emitter, square law (reducing field strength by the square of the distance) and part of the body in the main lobe of the field.  Resonance of the human body can enhance absorption.

Children, whose biological cellular activity is high due to growth may be more susceptable to genetic cellular damage than the adult population as a whole, yet they are becoming more and more long term users of cellular handsets.  Cell phones can radiate their half watt of energy in very close proximity to the head measured in centimeters.  If we were only concerned about easily quantifiable energy absorption as measured thermal affect in tissue, this might not translate as a significant exposure issue at least in the short term.  Study of the thermodynamic response of the circulatory system and the body's own thermal regulation tends to negate any fear of thermal affects at these low energy levels.  But the jury is still out about potential subtle interference with membranes and the biochemical dances taking place within living and dividing cells.  Could a rather tiny addition to the electric fields or thermal gradient within the cell help trigger genetic accidents?

I know of folks who are very sensitive to RF.  They actually get headaches and feel a bit sick when in the presence of fairly strong RF fields.  Some can't use a cellular handset for more than minute or two at a time.  Most of us are not sensitive to RF, good thing when it comes time for an MRI, but a few of my broadcast engineering collegues are.  Have there been any studies done to attempt to pinpoint why?

 

SledDawg
User Rank
Silver
blackberry blues...
SledDawg   11/28/2011 2:18:20 PM
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I'm in a geezer rock band that plays 60s tunes using mostly vintage tube guitar amps and such. One of our members has a pretty high powered (no pun intended...) corporate communications job that calls for him to be chained to his Blackberry at all times, lest a far flung exec need some speechifying advice. It has happened more than once that his device will BZZZZT through all of our gear and PA while we are on stage (at midnight, our time!) and he must drop his tambourine and head for the bar to take the call.

Ratsky
User Rank
Platinum
Re: RF disturbances more scary then an nuisance?
Ratsky   11/28/2011 2:41:45 PM
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In my post, I did point out that to my knowledge there has not been any study of hams re longevity or cancers; I think it could definitely be a worthwhile effort regardless of the results.  I've been out of the RF business myself, professionally speaking, for MANY years (over 35; even the last few years I was with Motorola, I had "graduated" to system-level design), so I don't have any personal stake in this battle.  I live in the Atlanta area, and right now, every night it seems the evening news is running yet another story about hysterical parents near-rioting over having cell towers anywhere near schools or residential areas.  Last night, one of those stated that there were 159 existing cell towers within 4 miles of the one she was protesting about.  The clear implication is "why do they need so many?"  Cell sites are NOT cheap to erect OR maintain; this particular one would result in $4 million INCOME to the school district (badly needed) over the next 10 years. It's needed because of the CONSUMER DEMAND (strongly encouraged by the current US administration) for vast increases in broadband data infrastructure.  The only way to do that is by cell-splitting (which incidentally REDUCES the radiated power from each cell site!); ergo, more cell sites and towers, covering the same geographic area.  The only way to stop this would be to outlaw smartphones (a "modest proposal" of Swiftian dimensions)! 

This is a needless pot-stirring (IMHO) by the technically-illiterate mass media.  EVERYONE who does understand the technical issues involved needs to help educate the illiterati and the public to forestall this sort of "pitchforks and torches" activism before it results in a further shackling of our ability to IMPROVE our lives and lifestyles with advancing technology by ill-advised and misguided policies.

ab3a
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Platinum
RF Ignorance
ab3a   11/29/2011 7:17:15 AM
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I have been a ham for 35 years. I've seen a lot of research. An epidemiological study of ham radio operators would have to take a whole lot of other extenuating circumstances in to the picture.  Don't forget about the wonderful materials we use to make electronic components and what happens to them if they burn up.  Don't forget that they often set up their stations in the basement, where radon is commonplace.  Don't forget that this is often a very sedentary activity. 

There are lots of reasons why you might find that ham radio operators may not be in the best of health, and none of them have anything to do with RF.

That said, knowledge of RF in general, is rapidly disappearing. Few people understand much about how the radio spectrum propagates, about impedance, about the practical limits to dynamic range and so many more very technical subjects.

Instead we have people who think they understand the time domain and they're reinventing all the frequency domain stuff to fit in those terms so that they can make software of the radio. I can hardly wait until the first of these people encounters a less than ideal amplifier and exclaims "I don't get it --I've got 18 bits of dynamic range!"

The beauty of the CDMA standards in use here in the US is that they don't make those pulsed transmissions that are so easily picked up by poorly shielded audio wiring.  Another good thing is that while RF is more ubiquitous today, it generally runs less power because it only needs to get to the nearest network node. After that, some other networking takes over and routes it to the destination. 

I sympathize with those who feel that RF is the cause of their weirdness.  I should remind everyone that by definition, RF radiation is NON-IONIZING.  Aside of heating effects, no-one has ever shown that RF radiation is dangerous to humans, plants, or animals despite nearly a century of research. I'm not saying that such an effect can not exist, but I have to point out that this electrosensitivity research, despite nearly a century of effort by many different people, has yet to produce any consistent and reproducible results.

cspacone
User Rank
Iron
Re: RFI on the Rise
cspacone   11/29/2011 12:46:12 PM
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 But as a product designer that routinely sees thier device used in the situation you describe below, one would think that they would put in a brick wall RF filter that would shunt everything from about 800mhz and above.

Any first year EE student could design a passive filter that would do the job and it would cost all of $0.50 to implement. Unfortunately the 'consumer' electronics industry has a long history of paring down designs for cost reasons, typically resulting in degraded or poor performance of the product.

It is the 21st century and RFI susceptance as you properly point out is a real and continuing issue. And the problem will only get worse as more and more wireless devices are unleashed and cost pressures continue to drive designs towards minimalist levels.

Cheers,

Chris Spacone

 

 

bdcst
User Rank
Platinum
Re: RF disturbances more scary then an nuisance?
bdcst   11/29/2011 12:52:14 PM
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I agree that the mass media often gets it wrong and contributes to mass hysteria about technology.  Problem is when there are alleged experts with opposing opinions the unwashed have nowhere to turn as they do not have the expertise to research the answers for themselves.  I put the blame squarely on the US education system both high school and college.  Liberal arts majors should be exposed to life skills knowledge that incluse science and technology for the non technologist.  And it should be a requirement, not an elective.

Ironically, those that protest cell tower placement increase their exposure to RF from their handsets by forcing them to put out more power to reach more distant cell sites.  They do not understand the physics or the technology and thus make the wrong decisions regarding RF exposure concerns.

 

 

bdcst
User Rank
Platinum
Re: RF Ignorance
bdcst   11/29/2011 1:26:20 PM
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RF radiation is called non ionizing as its energy level, based upon frequency (wavelength), cannot normally bump electrons from valence rings of atoms.  Thus the chemical reaction effects are considered to be non existent.  RF is part of the same electromagnetic spectrum as X-rays gamma rays and visible light.   The real question is, are there rare circumstances where RF energy can cause other biological changes.  And are those events frequent enough that they should be addressed.  Probably not.  But we do need long term studies to get results above the noise and decide once in for all if more or less caution is appropriate. 

Remember it is only in the past few years that we're all being exposed long term to SHF wavelengths from our cell phones, cordless phones, WiFi AP's etc.  Also, remember that with digital modulation the peak energy level is much higher than the average level.  So, if we are not dealing with tissue thermal effects, the average level becomes irrelevent.  Peak RF fields have to be treated differently.  When I specify a test load for a digital RF signal I need to know not only the average power dissipation required but the peak RF level in that waveform.  The peak results in higher voltage stress of the resistor.  Dummy loads known to work well at CW power levels have failed over time when subject to digital RF energy of the same average power because the peaks provided significantly higher voltage.

Human activity always results in benefits and problems.  Life is a tradeoff.  If we are too careful as a species we'll never progress.  If we are too cavaliere, we may end our reign on this planet way too soon.

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