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Monday, January 26, 2015

Does 5 nano watt per cm2 is a lot of radiation? Depends how you look at it!

In Israel (and maybe in other countries as well) When you ask for a professional RF tester to test the RF radiation levels in your house (coming from a cellphone tower nearby), it is most likely that her will write in the report "less than 0.1 uW/cm2" ( Some testers will write any value, even if very low). The opinion of the ministry of environmental protection, and of most testers, is that 0.1 uW/cm2 is very low and that there are no health effects, what so ever, in such low levels.
I, as an EHS person, know that they are wrong, and even levels bellow 0.1 uW/cm2 can cause damage and are not healthy.

But first, I must add that most professional testers in Israel operate their meters in such a way that the level is being average over the time of the measurement (this is protocol here). This cause the levels to drop considerably. I believe that the meters should be operated in Max Peak value so they will report the peaks and not the average.

In addition I have many doubts of the wide ban meters ability to sum up all the signals across the frequency range. I think this is because of their limitations and the way they operate. My professional opinion and estimation is that most wide band RF meters can't add and sum up all, and not even most, of the RF signal across the band. I think that the number of signals across the band have a very big impotency in the estimation of the possible risk RF exposure hold, and this number is being over look in most cases. In order to "see" these singles you need to use a spectrum analyzer and not a wide band meter.

In order to prove my point, I took my home use RF meter, a simple RF spectrum analyzer (RF EXPLORER), a camera, and walked to the next street cross. From that street cross and over the building roof tops, a cellphone's mast, with 3 sets of antennas, was visible, about 400 meters a way from me. The time of the measurement was a bit after 15:00, in a small neighborhood in the center of Israel.


The RF meter , after several seconds of measurement, showed the max level of 0.0539 mW/m^2, which is 0.00539 uW/cm^2, which is 5.39 nW/cm^2:



At first look it looks as a very low level, right?
But what hides behind this "low level"?
How many signals are combined to this "low level" and what is their level"

In order to answer these questions, I pulled out my home use RF spectrum analyzer, The RF EXPLORER. I configured it to sweep between 1800MHz and 2400MHz, and in MAX HOLD mode so the max sampled signal was kept on the screen until a stronger single replaced it.  The picture that was created after few seconds showed at least 7 RF signals, pretty much in similar levels. I can only assume that every one of these signals is complexes out of many short band signals. This is how it looks:


As I said before, when you look on the frequency span, the RF radiation does not look so "low level" does it (and this is just a small part of the full band. I assume that in the other parts there are many other signals, maybe hundreds)?
Every one of these signals, may interfere with biological system in general and our nerve system in particular.
Every one of these signals is not natural, in fact the natural RF level should be around -110 dBms (if I am not mistaken). 
So what does a measurement with a wide band RF meter is good for?
What does it shows?
Does it show the strongest signal, or maybe few of them?
What would a measurement done with a slow RF meter, that was calibrated according to single signals and was operated in average mode will show?

Do you have an answer? write it bellow!



P.S. - I still think that a home use RF meter is the easiest-cheapest-fastest way to "see" radiation, but we must keep in mind that it "shows" us only part of the picture. Regarding professional testing done in Israel, it shows what they want us to see, a partial-calming picture.



3 comments:

  1. OK, so basically how much radiation did you measured with the spectrometer in terms of µW/m2 on the different bands ?

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    Replies
    1. In the equipment I have it is almost impossible to calculate. It should be something about 20-40mW/m2.
      The point is, the low measurement is not the full picture. The full picture is that there are many signals even if the levels are relatively low.

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  2. Amir
    You ask an important question - which is why, for years, I have been saying that the important metric is the peak signal strength (usually measured in volts per metre (V/m)) and not power flux density (PFD). It is why my designed Acoustimeter shows both (and we have improved the very short pulse performance of that recently). Power is energy summed over time - which should really be at least a second and for ICNIRP, etc, is usually 6 minutes.
    Electronic equipment interference (EMI) is protected against by EMC rules - and they almost all rely on signal strength in V/m as the thing that will cause interference - not PFD in uW/m^2.

    Almost all non-thermal level RF meters actually measure V/m and then those than display power convert this numerically to the equivalent CW power value. In fact that over-reads GSM signals and under-reads 3G/UMTS/4G/LTE signals due to their spread-spectrum nature and their very fast changing amplitude profile due to the abrubt phase jumps.

    A fast acting peak reading broadband meter is the best meter for people to use to protect themselves in my opinion. Spectrum analysers are expensive if they are any good, complicated to set up and use properly (my $10,000 Anritsu has over 100 different set up parameters!) andall but $100k plus ones scan across frequencies in a way that will often miss short intermittant signals completely - the pulses occurs when they are measuring a different frequency -or you set them on peak hold for ten minutes an see some short peaks that only occur every few minutes - how do you evaluate their contribution to the overall signal - their PFD is tiny - but they may be very disruptive to sleep. They are a useful analysis tool, but, in my opinion, not a useful "am I being zapped" meter equivalent.

    This is a big debate - too big for this feeback box. I will forward you some content from recent scientific email exchanges about changing signals over time and modern electrosmog.

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