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Sherlock Ohms

The Case of the RF Disturbances

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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.

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?

 

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: 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.

OLD_CURMUDGEON
User Rank
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!

itstechpro
User Rank
Iron
Re: Just Bzzt on the stereo?
itstechpro   11/28/2011 10:46:24 AM
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In 1976, I was working on a low noise video amplifier for a large area CCD array to be used in astronomical observation. When measuring noise figure and bandwidth, I was plagued by a periodic noise burst that made the measurement impossible.  I checked for sources around the lab and then around the house (lab located in the basement of a hillside home in Fairfax, Marin County, CA.)

Finally, I happend to glance out of the window at the fine view of Mount Tamalpais which we had and recalled the Air Force search radar at its peak.  I could see the radar site (~7 miles away) through binoculars; the rep rate of the interference was what I would have expected from the rotation rate of the antenna.  A small Faraday cage around the measurement setup took care of the radar interference.

SSLGuru
User Rank
Iron
Re: Just Bzzt on the stereo?
SSLGuru   11/28/2011 10:32:24 AM
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 I grew up next to a US airbase - in the UK. In the late 70's / early eighties, there was a well known stretch of road adjacent to the air base along which cars had a habit of stalling - dead in their tracks and for no apparent reason. The emergency service crews - AA and the like (UK's equivalent of AAA) - had learnt that the best means fo starting a stalled car in that location was to push the car a few hundred yards down the road. The car would then start with no problems. The problem was sufficiently serious to warrant mention on the local news I recall.

 In that cold war era the authorities denied all knowledge... plus, it only seemed to happen to what were then Japanese imports, so nobody seemed to worry much at the time. (Presumably Japan was using electronic ignition a few years before the homegrown competition).

 I work in solid state lighting. It is amazing just how much equipment is available today with no FCC marks on it. There is bound to be fallout from that as its use spreads. I have one very widely used driver on my desk here today which comlpetely knocks out any fm radios within 20 feet of it. (But who uses those these days I guess??).

 In the 60's and 70's when television was analogue broadcast and the receiving equipment still a work in prgress Joe Public knew all about interference. We can expect the same awareness to arise as the internet of things grows over the next decade and various day to day items stop working for no reason.

We will see jobs, legislation and associated corrective action on multiple fronts as a result.

JC, NYC USA

 

Battar
User Rank
Platinum
Just Bzzt on the stereo?
Battar   11/28/2011 9:44:00 AM
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A long time ago I worked at an intstallation in a Mediterranean port. When a USN sixth fleet carrier was visiting the port, NOONE could watch television or listen to the radio - the inteference from the ship's search radar was just too much. Don't know why they operated the radar in port, but they did.

jmiller
User Rank
Platinum
Re: RF disturbances more scary then an nuisance?
jmiller   11/27/2011 8:40:53 PM
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Did you happen to let any of your neighbors in on the issues with your apartment or was it just every man for himself.

TJ McDermott
User Rank
Blogger
Re: RFI on the Rise
TJ McDermott   11/27/2011 8:33:11 AM
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Isn't there a tag or blurb on all electronics, required by the FCC, stating something like "this device causes no radio interference, and will tolerate any interference that in the environment"?

The only instance in recent memory where interference was acted upon was LightSquared's network causing GPS interference.

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