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Author Topic: Electromagnetic energy in "air"  (Read 3760 times)

Offline Tom 2U

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Electromagnetic energy in "air"
« on: 11/01/2006 08:28:48 »
How much of the electromagnetic energy (compared to background/natural) in the "air" in west European countries is due to human activities?
Have this energy decreased after the introduction of digital techniques in communication? (The old analogue mobiles had higher effect than the new digital)


 

another_someone

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Re: Electromagnetic energy in "air"
« Reply #1 on: 11/01/2006 14:15:00 »
I cannot answer the question regarding how much of the energy is man made (except that in the radio frequencies, I would imagine it is the major portion of it), but I would have thought the introduction of digital would have increased the amount of noise energy (if not the amplitude of the noise).  One reason for the increase in energy is because digital tends to operate at higher frequencies, and the energy of a wave is proportionate to its frequency.  What has helped reduce the noise from mobile phones is various battery saving technologies that reduce power output when the base station is close by.  Mobile phones aside, we have WiFi and Blue Tooth networking, radar signals, radio altimeters, GPS satellite signals, satellite broadcast signals the range of products that are transmitting at the higher frequencies is ever increasing.

Another aspect you have to take into account is that a lot of electromagnetic noise is not generated by systems that are not deliberately broadcasting radio signals.  A PC is operating in the gigahertz frequency range, with various clocks generating internal signals at hundreds of megahertz, and then also generating harmonics above that.  I have found the cable leading to the computer monitor has a particularly noticeable effect on my nearby radio receiver.

Electric motors are famous for generating unwanted radio signals.  These are very wide band, so even if the amplitude in any one band may be small, the amount of energy across the bands can be significant.

Finally, ofcourse, electrical transmission lines are broadcasting massive amounts of radio traffic in the ELF band.  These are very low energy because of the low frequency and very narrow bandwidth, but very substantial amplitude of signal.
 

Offline DocN

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Re: Electromagnetic energy in "air"
« Reply #2 on: 11/01/2006 16:55:50 »
I heard someone who jokily said that the reason UFO's have never landed on Earth, was do to their reception of our radio and tv signals!  
Doc
 

Offline DoctorBeaver

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Re: Electromagnetic energy in "air"
« Reply #3 on: 11/01/2006 17:07:23 »
This post has brought to mind something that happened when I was working for Lucas Defence Systems many years ago.
There was an apparent problem with a particular type of microwave radar source. In the QA dept there were 2 part-time testers - 1 worked mornings, the other worked afternoons. The 1 who was working afternoons kept sending the sources back to the development dept saying there was a strong, spurious signal. Because of the admin systems in place, the sources didn't get back to the development dept until the next morning. Our engineers were perplexed because they couldn't find a problem, and sent the sources back to QA. Again they were returned to development because the spurious signals were still there.
It was thought there may be a problem with the test rig this particular QA tester was using, so a different 1 was used. The signal was still there.
It took quite a few days investigation before it was discovered that the spurious signal was, in fact, BBC2! This was in the days before BBC2 was all-day & it didn't start until about 2pm.
Once the cause was found, it was simple matter to tweak the sources to eliminate the signal.
What made this incident even funnier was that the sources were for missiles and the BBC2 program concerned was Playschool! I could just imagine Floella Benjamin saying "Let's look through the round window. Oh look... there's an out-of-control missile out there!"
 

Offline Soul Surfer

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Re: Electromagnetic energy in "air"
« Reply #4 on: 11/01/2006 23:22:27 »
An interesting question but the answer depends on what frequencies of electromagnetic radiation you include.

If you only consider very low frequencies and up to the migrowave band most of the energy is probably due to human activity but the total energy is very small unless you happen to be dangerously close to a transmitting aerial. (like less than one metre from a high power transmitter).  If you include all electromagnetic radiation you must include the infra red band which is where most of the energy radiated by the objects around us comes from, but that is totally dominated when our major local source of electromagnetic radiation is operating, that is the sun which prooduces a good deal more energy in the light and near infra red frequencies.  Above these frequencies in energy terms the radiation is very small indeed.  We can all tell this by using our own built in detectors, because we may feel warm around the house but will feel quite hot if the sun is shining. The radio waves we absorb will not significantly raise our temperature.  In general the biological effects of non ionising electromagnetic radiation are only related to the thermal effects that they produce.  That is because they are totally dominated by the electromagnetic radiation that our bodies generate themselves by being warm.

By far the strongest source of radio frequencies we are likely to subject ourselves to is by using a mobile phone and it may just be possible to feel the warming produced by this but it is a good deal less than full sunshine.

As far as the difference between analogue and digital radio signals, It doesnt matter much, but as digital signals nowadays can transmit information much more effectively than conventional analogue signals we can and will get a lot more services with a small reduction in total power transmitted as the transfer to digital transmission becomes virtually total in a few year's time.

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« Last Edit: 11/01/2006 23:31:05 by Soul Surfer »
 

ROBERT

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Re: Electromagnetic energy in "air"
« Reply #5 on: 13/01/2006 10:53:28 »
quote:
Originally posted by Tom 2U

How much of the electromagnetic energy (compared to background/natural) in the "air" in west European countries is due to human activities?
Have this energy decreased after the introduction of digital techniques in communication? (The old analogue mobiles had higher effect than the new digital)




I think Tom 2U is referring to the fact that the old analogue network had a lower concentration of repeater stations (masts), so the RF power output of analogue handsets/repeaters was higher than in the current digital network.
« Last Edit: 13/01/2006 11:04:16 by ROBERT »
 

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Re: Electromagnetic energy in "air"
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