Standard Method to Take Ambient RF Readings

I have a couple of handheld RF meters I use in the lab. Recently I was asked to take some ambient readings around a several block area, near a school, where there are cell towers nearby. I would like to do this according to the "standard" practice, but I am uncertain exactly what that is.

For example:

How closely spaced should the measurement sites be, so as to form a kind of grid of "overlapping" readings?

How long to time each reading with max hold enabled?

Whether to use dB, V/m, or W/m. I have seen all used. Is there a convention for this type of reading?

Any recommendations on this would be appreciated.

Richard Clarke

PS: Let's not get into a debate along the lines of "foil hats", etc. I don't have any idea one way or the other, and that's how I like it.

Reply to
rclarke
Loading thread data ...

Sounds like a job for a spectrum analyzer, m8.

Reply to
Cursitor Doom

Thanks but all I need is the overall RF background level, not measurements at discrete frequencies. That's what my meters do. Anyway, I don't have a portable SA.

Richard Clarke

Reply to
rclarke

If you don't look at the specific frequencies, how will you know if it is coming from the cell tower(s) and not some buried power line connecting the street lights or some AM radio station?

What do the instructions for your "meters" say?

Take a gander at FCC Bulletin 65 at FCC.gov

Good luck, tm

Reply to
Tom Miller

What sort of center frequency and bandwidth do these handheld meters have? How will you know what part of the field you are reading is contributed by the cell towers?

Given a broad enough bandwidth, you could be reading the field produced by a nearby AM radio station. Or even the 60 Hz power line.

--
Paul Hovnanian     mailto:Paul@Hovnanian.com 
------------------------------------------------------------------ 
 Click to see the full signature
Reply to
Paul Hovnanian P.E.

Congratulations! You have stepped into a swamp. I think the alligators know where you are, and are being polite, waiting until you make noise to pounce.

A possible way out of the swamp? You're busy and can't do such testing yourself. Offer to get together with some of the interested parties and show them how to use your equipment to take measurements, and offer to rent them your valuable equipment so they can go collect data. You could even mention some of the difficulties in analyzing such data and drawing useful conclusions from it.

Take a look at survey meters by ETS Lindgren, and the documentation for those products. Their equipment (when calibrated) does a superb job.

But as others have pointed out, such devices are integrating, covering basically DC to light (or to 6 GHz for some of the ETS Lindgren stuff).

Low readings are good -- nothing around (plenty of definitions of "low" based on E-field strength or power density).

But high(er) readings -- what are they from? Now you need the portable SA, unless you can use simple physical methods to identify a likely candidate (such as a Lightspeed or other fiber to copper interface, or leaking cable TV boxes).

If your gear is flat (or at least calibrated with a known response) to

1900 MHz to cover cellular, is it flat up to 2.5 GHz for WiFi? 5.5? How can you tell if the reading you're getting is from the cell tower 50 feet away and not from the house behind you where the owner is trying to compensate for his Wi-Fi not working in parts of the house by using equipment not quite approved by the FCC?

By all means, have fun. You could wander around and collect data, and try to see if it makes sense. Don't know if I'd share it with anyone, though. Really smells like a lose-lose situation to me, even if all you get is low readings. For if you do, there will be those that claim you are one or more of: (1) in cahoots with the other side and hiding data, (2) an idiot who doesn't know what he's doing, (3) using the wrong equipment, (4) using uncalibrated equipment, (4) using equipment incorrectly, (5) not qualified to make these measurements, (6) a member of the wrong political party, (7) you get the ides...

Reply to
artie

The standard practice is to use a calibrated antenna, and a radio (or a spectrum analyzer, but usually that's just to speed things up). There's a coarse sweep first, to identify interesting parts of the spectrum, followed by hand-tuning to peak frequencies and taking long-time average measurements on those frequencies.

Nowadays, all the personal electronics of pedestrians will be a major component; you'll want to do all the measurements during peak occupation hours of the school. And, you'd better put your own phone into a shielded enclosure (paint cans work well), or yank the battery.

Reply to
whit3rd

The maker and model numbers would be useful. What is appropriate equipment for a laboratory environment may not be suitable for outdoor use. For example, your equipment may be single axis, while a proper exposure meter is 3 axis. There are also differences in frequency coverage and sensitivities. Measuring RF from a cell site with a broadband meter is problematic if it's mounted on an FM broadcast station tower.

If you're trying to measure the radiation from a specific source, methinks a spectrum analyzer would be more appropriate. If you just want the total RF floating around the area, then a handheld exposure meter is more suitable.

The manufactory usually has literature on their web pile for how to use their devices:

It might also be helpful to look at prepared reports by EMF measurement services:

The FCC has some guidelines:

Measuring at human head height is fairly standard. I don't know about grid spacing. For cellular, what is usually wanted are the location of hot spots or the maximum RF field locations. For average levels, I just pick an open spot where there a few variations in intensity. That's certainly not standard practice. Actually, I don't recall any guidelines as to measurement spacing. Obviously, the more readings, the better.

Averaging time for FCC MPE is 6 min and 30 minutes. See 47 CFR 1.1310

It's by whatever agency or organization you're trying make happy. FCC MPE power density is in mW/cm^2. Field intensity is in V/m. Here's a typical report for a PROPOSED cell site: Since it's a proposed site, there are no measurements involved, but there's plenty of good info inside.

I think you'll also find this handy:

Awwww... y'er no fun.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
 Click to see the full signature
Reply to
Jeff Liebermann

I forgot to mention that you should customize your units of measure for the expected outcome and target audience. (I've actually done this several times). For situations where you want the results to look like everyone is safe, use Watts and meters, which produce small numbers that look ummm... small. For the tin foil hats that are looking for big numbers to make the signals appear more objectionable, use mW and cm which will produce much larger numeric values. Everyone knows that big numbers are dangerous.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
 Click to see the full signature
Reply to
Jeff Liebermann

According to the old saying, if you want to be sure about your measurement result, just take only on reading :-) :-).

You should get the readings for both horizontal and vertical polarization and also aiming the antenna at different directions if the antenna has some directivity. An (horizontally) omnidirectional vertical monopole is usually sufficient to get reading for vertical waves, but you might need something like a Big Wheel to get an omnidirectional radiation pattern for horizontally polarized waves.

For indoor measurements, perhaps 5-10 cm., for outdoor measurements in a residential area, perhaps 1-2 m, in rural areas tens or hundreds meters at least in the far field.

You should measure the average _power_ integrated of the power specified in various standards. There is no point in measuring instantaneous (with or without peak hold) e.g. in V/m.

integration and then you can express it in one of those units.

Please note that if you are making some measurements with some exotic antennas, people are going to look at you and take pictures of you and send them to youtube etc. Thus there are going to be close transmitters that might be far stronger than a base station.

The problem is that those who requested the measurements are not going to be able to interpret the results :-)

Reply to
upsidedown

From the replies so far, I think I should perhaps clarify my original post.

I understand the value of a SA, but all these folks want is the _overall_ exposure level, excluding 60Hz. My RF meters will do 100MHz to 8GHz so that is what I was going to provide, taken at various geographic intervals to form a kind of "map" of local field intensities.

Both of my meters have short whip antennae, not triaxial or log periodic, which I understand are suited to separate 3 axis measurements only.

I imagine the vertical axis would always give the highest outdoor reading, so that was all I had planned.

Again, I would not try to "blame" anything on the towers, and really wounldn't get involved in the complexity of measuring them as a singular source.

Any further suggestions for the scenario I have described above?

Richard Clarke

Reply to
rclarke

Unfortunately there's a bunch of loonies around who believe that even tiny levels of RF radiation (like you might get from a Bluetooth device) are somehow injurious to their well-being. Some of them even up sticks and relcoate to isolated territory in an attempt to get away from radio signals. They'd do better by spending a spell or two in a mental hospital, IMHO.

Reply to
Cursitor Doom

What you'll be doing is mapping the strength of the strongest source. Anything down about 10dB from the strongest source is not going to contribute much to the total. If there's a cell site nearby, that's probably going to be the strongest. With a spectrum analyzer, you can keep them separated and map each source individually.

Using a meter that goes from 0.1 to 8GHz is somewhat overkill at the high end, and is missing lots of RF sources at the low end. To measure 60 Hz, you're probably measuring the magnetic component instead of the electric.

Yep. You need 3 antennas to do it right.

Nope. For power lines, which are horizontal, the horizontal gives the best coupling. Same with TV and FM stations, which are also horizontally polarized.

Instead of your expensive analyzer, I suggest a cheap EMF meter found on eBay. For example: $12 It will measure fairly strong fields from 50 Hz to 2GHz. That's probably sufficient to determine if there's anything dangerous in the neighborhood, which is what I would guess inspired this adventure. AT the price, you could probably donate on the individual who suggested the idea. The problem is that such cheap devices are not very sensitive.

Like I said, y'er no fun.

Hang a data logger on the detector output. Record GPS location and EMF level. Find a plotting program that will produce a "heat map". Something like this used for Wi-Fi mapping. Wander around collecting data and see what appears.

Also, I think going down to 60 Hz is a bad idea.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
 Click to see the full signature
Reply to
Jeff Liebermann

** I typed "cell tower radiation levels" into Google and this was the first hit:

formatting link

Some common sense advice from folk who do the exact job you have been asked to.

They might rename their business " Paranoia Busters" one day....

.... Phil

Reply to
Phil Allison

You'll have to cite a whole pile of sources to make any sense of that...

  1. ELFs go right through pretty much everything not made of copper. What's it going to do?
  2. Precession, if you're referring to nuclear magnetic resonance, is an extraordinarily weak phenomenon, particularly so at room temperature and Earth's magnetic field strength. On the order of microelectronvolts, and useful populations of parts per trillion. (Nuclei in a magnetic field align either parallel or anti- to the field, with a small energy difference between the states. The difference is proportional to the applied field, and therefore, the energy/frequency of the photon which interacts with it. If the energy difference is very small relative to thermal energy, the populations are very nearly equal, and only a minute difference can be sensed externally -- like a two party democratic vote, the rest cancel each other out.)
  3. Ca43 (0.145% abundance) is the only stable isotope of calcium with a nonzero spin. Not a very strong signal (not always a problem for NMR, but if we're talking weak fields here, well..). The other 99.985% is unaffected by E&M. FWIW, the resonant frequency would be ~143Hz in Earth's magnetic field, give or take an octave depending on where you are.
  4. You're probably not referring to EPR (electron paramagnetic resonance), which only applies to radicals, which are only present transiently in biology. Ca(2+) is not a radical and does not exhibit EPR.
  5. Atomic electrons, in general, don't experience any functional effects, at least until extraordinarily high field strengths (gosh, 100s of T?). I should imagine many chemical reactions proceed somewhat differently at those field strengths, but I don't know by what mechanism they would, and I haven't heard any research suggesting there is an effect. (A possible mechanism could be different energy levels in spin alignments between atoms, resulting in slightly different reaction rates -- the rates probably would matter more for small-energy-difference reactions, such as are common in biology. The result would probably be analogous to drinking an awful lot of heavy water -- at high enough concentrations, the DHO and D2O finally start to slow down or distort proteins and such, but it takes an awful lot to get there.) Only thing inbetween is -- like the nuclear case -- the splitting of spectral lines.
  6. Even if there were a known nuclear or electric interaction with ELFs, there is no known mechanism where exciting or interacting with these phenomena causes chemical effects, let alone the disruption of biological pathways (at least, of those we know about).
  7. What value are you talking about? Amplitude, frequency, some combination thereof?
  8. Probably because there isn't any solid peer-reviewed historical data suggesting such things...

Tim

--
Seven Transistor Labs 
Electrical Engineering Consultation 
 Click to see the full signature
Reply to
Tim Williams

Thanks. That's good to know. But how does one take an averaged horizontal measurement with a meter that has only a whip? Set to max hold, hold it horizontal, and spin around a few times?

Cehck out "RF Explorer" for a cheap spectrum analyzer.

That's a really great program. Amazing what you can get for free.

Agreed. Apparently the worst gremlins live in RF land anyway.

Richard Clarke

Reply to
rclarke

It was really a simple observation and much confirmed by your responses, especially 1, 6, 7, and 8. My statement was meant only to raise questions to make people keep an open mind, rather than 'turn a blind eye' and completely dismiss any potential understanding of the subject. That said,

*IF* research on biological impacts has been done, and I mean legitmately done/reported, using precepts involved with potential biological interaction and have all resulted in negative results of finding any relationships; then and only then, I'd totally agree with the attitude to dismiss, forget, go onto bigger problems.

But you have to admit, that *if* there is a propensity for a biological response in a statistical group, and *if* that response is triggered by a range [amplitude range given the fixed field], not an 'exceeded' level; the likelihood of finding such a relationship in historical data is nil.

One potential site of such historical data occurred about 2 blocks from where I lived. A federal building with two wings built same time sharing the same building materials sharing the same electrical distribution system sharing the same HVAC mechanicals, etc etc had an occurrence of 'sick building syndrome' in the west wing only. There were some 8, or was tht 15?, cases of one of the rarest forms of lethal cancerous brain tumours. One young victim's widow sued, appeared on Jiraldo Rivera's TV Show with her lawyer, whom I personlly know. Sad, very sad. The state launched a very lengthy, and if you saw the report, well done investigation looking for a potential cause, after years of effort, evening monitoring the 'flashing' of the local airport's radar system, found no definitive reason for the illnesses. In other words, they found NO difference between the two halves of this building.

Living nearby, I saw something that differentiated the two halves and contacted the California epidemioligist assigned to the case with the intention of having her expand the investigation into exploring the concept. During our conversation upon telling her my observation and potential cause, she added another piece, she said this form of tumour is usually very slow growing, occurring in almost everybody. It's just that people usually die of old age first, before any symptoms occur. She went on to say she'd found many 'starting' tumours in her autopsies. Unfortunately, no interviews with anybody were conducted to explore, case got closed, and the reports got published. And, very expensively the potential source was completely removed. No more cases appeared. Coincidental? perhaps.

The potential source: along the west side of the building, across the street along Guadalupe Parkway ran major distribution electrical towers. In summer the wires would droop dramatically bringing the wires VERY close to the ground. These wires, according to PG&E, the utilities company, were 'double cabled' and carried over 1000A, sometimes 500A sometimes 1500A depending. The fields from these wires penetrated the west wing slightly more than the east wing, but just a bit. But, more importantly to me, what I saw was that people in the west wing would park underneath the wires, in a makeshift parking lot [it was much closer than the allocated parking to the north] When I say, makeshift I mean makeshift. As in, never lost a car in wet weather makeshift. Twice a day, or more often, people would expose themselves to some of the largest, and most varying, ELF in existence. Shortly after the 'sick building syndrome was reported, that parking area was fenced off with no allowed access. Within a few years, under the justification of 'beautifying' the high tension wires were placed underground. Thus, ended the 'sick building' in San Jose. Could be coincidence, might not be, I just say let's keep an open mind here.

If there is some relationship, I'm open to not applying culpability to the utilities companies, as long as they followed 'best engineering' practices at the time. However, if they have accumulated evidence and have purposely been obscuring that evidence to avoid culpability, and therefore also preventing changing of 'best engineering' practices...

Reply to
RobertMacy

You don't measure average. You're looking for the worst case RF level which means peak. You can do it with a single axis whip antenna by waving it around until you get the highest reading. That's a PITA and produces bad numbers because with a whip antenna, the case of the instrument, and the possibly the operator become part of the antenna system. You want the antenna and sensor to be physically separated from the instrument and operator so that they don't affect the readings. That's why the real instruments have antennas/sensors that look like a golf ball on a stick.

Repeating again, if you're trying to get the ambient signal levels in an area, you're probably ok with using a broadband device. If you want to determine the signal levels produced by a known source, such as the cell sites, you'll need a frequency selective device, such as a spectrum analyzer. If you have multiple overlapping sources, as you would with a typically congested cell tower, you'll need to do quite a bit of math in order to obtain a realistic "ambient" average.

There are cheaper devices for the purpose. For example: Note that they have a built in antenna which is quite directional. For these, to obtain a peak reading, you just point it at the RF source or just wave it around looking for the highest reading. Take a bunch of such readings, grind the numbers, calculate an average value, and you have the average ambient level. Incidentally, the term is now "electro-smog".

Anyway, if someone is worried about bad RF from a cell site, you might inform them about Ogronite, which has the amazing property of converting negative energy into positive energy.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
 Click to see the full signature
Reply to
Jeff Liebermann

Maybe some epidemiology will help. This is a graph of the new incidence of brain and central nervous system cancers in 9 major metropolitan hospital areas, where statistics were collected from 1975 to 2006. Note that the incidence of new cases is roughly flat at between 6 to 7 cases per 100,000.

During the same time period, the use of cell phones and the corresponding exposure to RF has increased dramatically. Cell use took off starting in about 1990. In 1975, they were quite scarce. If there were any correlation between cell phone use (and RF exposure) during this time period, I would expect to see a corresponding increase in new cancer cases. That hasn't happened.

I give a short song-n-dance on the topic occasionally, mostly to clubs and civic groups. A common question is if there might be a time delay between exposure and the onset of symptoms, which will not appear on the graph. I found that such delayed symptoms tend to follow a bell curve, where some people exhibit symptoms almost immediately, while others show no symptoms, and the majority at some point in the future, which is the claimed delay. There's no evidence of any such bell curve on the graph.

Incidentally, the ramp up and peak at 1987 was due to the introduction of positron emission tomography diagnostics for cancer, which allowed earlier detection. This caused a slight increase in the incidence rate as more cases were diagnosed earlier. However, once this became widespread, the incidence rate slowly returned to it's previous level.

As an aside, there's also a common question about exposure to children, where growing bodies are allegedly more susceptible to RF damage. This curve is the incidence rate by age from 1992 to 2006: Note that the bulk of the brain cancer cases occur at age 50 and above. If RF were responsible for brain cancer, the heavy users of cell phones, such as young adults, would have a higher incidence rate that seniors, who hardly use cell phones.

If you're into this, you can do your own graphs at:

The problem with all this is that it's fairly easy to prove causality in the courts. One anecdotal case is often sufficient. Proving that something is totally safe is impossible.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
 Click to see the full signature
Reply to
Jeff Liebermann

headset 2 cm from your head (just out of the near field) and also

strength will be generated by a Class 1 Bluetooth or WLAN device (+20 dBm, 100 mW) at 20 cm from your head or by a single channel (10 W) base station at 2 m or a cellular site with multiple channels (100 W) at 6 m. A 50 kW AM broadcasting station would generate the same power density at 135 m.

Looking it the other way and assuming a multichannel (100 W) base station at 30 m would create the same power density as a WLAN (100 mW) at 1 m or a 1 mW headset at 10 cm.

While I would never look into an open waveguide or horn antenna, without verifying that the DC power has been disconnected, I have no problem standing in front of a parabolic reflector with transmitter activated. In fact I would hesitate to stand in front of an 1 m reflector with some significant RF power applied, but I have no problem standing in front of a 30 m reflector with the same power applied.

While most people would run away screaming if such a big reflector would be aimed towards them, the larger the reflector, the lower power density and hence smaller absorbed radiation levels.

Reply to
upsidedown

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.