cellphones and monitors

[Zener_Diode]

Hey
does anyone knows why cellphones effluence on pc's monitors?
the scaning lines freq in monitor is 15625Hz (or somthing around) the cellphones works on 800/900 MHz.
can someone has a good explanation?

 

[Nigel Goodwin]

Hey
does anyone knows why cellphones effluence on pc's monitors?
the scaning lines freq in monitor is 15625Hz (or somthing around) the cellphones works on 800/900 MHz.
can someone has a good explanation?

The scan frequency has nothing to do with it, it's the wiring in the monitor (which will be considerably higher than 15,625 anyway - that's PAL TV) directly picking up the high power RF transmission close by.

 

[Zener_Diode]

ok, but why we see the influece of RF trasmission which is 800/900MHz, even if it picking it up, you shouldn't see it becaouse of high freq, am I wrong?

 

[Hero999]

Yes, you are wrong, providing the signal is strong enough the frequency make no difference, it will still cause interference.

 

[HarveyH42]

What you see on your monitor is happening to your brain cells...

 

[RadioRon]

There are several ways that Radio Frequency energy radiating through space can interfere with other electronic devices. The most obvious one is if the other electronic device is a radio receiver tuned to the same frequency, and yet this is the most rare explanation. The most common form of interference occurs when the RF energy is turned into conducted voltage and current on a wire that is inadverdantly acting as an antenna. This RF power flowing on the wire is still at 800 MHz, but when it flows along the wire and hits the semiconductors in your electronics it gets converted to low frequencies through various processes including AM demodulation and through mixing with other oscillators inside the equipment. You see, most ICs, all diodes and all bipolar transistors contain PN junctions. These PN junctions are simple AM demodulators and when you put a high frequency EMF across them, they rectify the RF which converts much of the power of the RF to a baseband (low frequency) signal and this appears in your equipment. The stronger the signal the more you get baseband voltage appearing in your device.

Many cellphones use the GSM communications standard for voice. This is a Time Domain Multiplexed system so your cellphone is transmitting with very rapid on/off pulses, it is not transmitting steadily. These pulses are being picked up by nearby wiring in the monitor and other equipment, they are being rectified and so you have electrical energy at the pulse frequency which is in the audio range, I think around 220 Hz. So if this happens to audio equipment you hear buzzing when your cellphone is transmitting.

As most Ham Radio enthusiasts know, when you get interference of this sort, it is a sign that the device that is receiving the interference was not robustly designed. All governments issue radio licences to those controlling the radio equipment (in this case the cell system operator) which grants immunity to complaints of rectification interference. This immunity is not, however, extended to license-free radio devices (such as those certified or verified as Intentional Radiators under FCC part 15 in the USA) which includes most of the radio transceiver projects discussed on these boards.

 

[akg]

That's an excellent explanation Ron .

 

[StopGo]

What you see on your monitor is happening to your brain cells...

Hahaha.. my brain cells work at a much slower frequency

 

[HarveyH42]

Hahaha.. my brain cells work at a much slower frequency

Then I'd guess it could only help...

It's amazing just how small phones are getting these days. Won't be long before somebody will be able to superglue one to a rat's head and see how long he remains functional...

I remember reading that the four main brain waves are measured in th 1-4 Hz range.

 

[Hero999]

And your body is far too small to act as an antenna at that frequency. Radiowave are non-ionising radiation and can only damage you by heatin, all that stuff about mobiles causing cancer is pure rubbish.

 

[Nigel Goodwin]

all that stuff about mobiles causing cancer is pure rubbish.

Probably?.

 

[RadioRon]

all that stuff about mobiles causing cancer is pure rubbish.

Ah, an interesting topic. From what I read, the scientific community is still "out" on this one and have come up with little or no hard evidence that RF causes cancer or other cellular problems other than from heating. But they continue to investigate. Why? Because the public has already decided that its a problem, never mind the scientific evidence. One only has to try to put a cell phone base station on the roof of a school to discover the true beliefs of the community. For that matter, try running a high voltage distribution line through a neighborhood and see how much people fear the presence of those low frequency magnetic and electric fields (not RF but a related issue of "fear"). I believe that the FCC rules on RF exposure (sometimes referred to as the SAR rules) exist partly because of public pressure that some limits be placed on RF exposure, even if the only proven affects are thermal. The current climate appears to be that the public fears RF and low frequency EM and this fear will not be easily dispelled regardless of the facts, now or in the foreseeable future.

Reminds me of the other classic fear, that of getting the bends if you go swimming shortly after eating food. No scientific evidence for it, but everybody knows its true, right?

 

[dknguyen]

Apparently electromagnetic waves do polarize your brain juices. Didn't you learn that in your electromagnetics class? Whether it is enough to concern you or not is up to you.

 

[Nigel Goodwin]

For that matter, try running a high voltage distribution line through a neighborhood and see how much people fear the presence of those low frequency magnetic and electric fields (not RF but a related issue of "fear").

As I understand it legislation in the UK limits how close pylons can be to houses?, a number of years ago they moved the pylons behind my house further away - presumably because of this?. It's amazing how fast they can move them, it was almost like magic.

Incidently, after heavy snowfall in 1990, we had no electricity, no water, and no phone for ten days - it was particularly annoying to hear the HV cables in the field buzzing and crackling away! - apparently they are part of the 'super grid', whatever that is?.

However, I don't know how far the legislation goes?, behind me they are in an open field, so were easily moved. A friend of my daughter's actually lives directly underneath high voltage lines (300,000V) next to a pylon - but they haven't moved those, but it is in a housing estate and would be far more difficult (I suppose it's always possible they aren't used any more?).

Reminds me of the other classic fear, that of getting the bends if you go swimming shortly after eating food. No scientific evidence for it, but everybody knows its true, right?

Never heard that?, what I have heard is not to eat before ANY exercise (but particularly swimming) to reduce the risk of stomach cramps - I suppose it's worse while swimming because you might drown?.

 

[HarveyH42]

The 'bends' is expanding gasses in the blood while ascending to quickly (scuba diving). The abdominal cramps from eating before swimming... I was on the swim team from 9 years old, all through high school, never once a problem. A lot of leg cramps though, but that was probably another issue...

Who funds the research? Usually a huge influence on the findings and disclosures. If you piss offyour employers, no more money, not to mention might effect future employment. Aren't the better research jobs, the ones where you aren't really expected to produce anything?

Human body not big enough to act as an antenna? Why do people get struck by lightning then? What about metalic dental appliances? Not to mention the transmitter is almost embedded in most cellpone user's skulls. High tension power lines and transmitter towers are generally atleast 30 feet in the air...

 

[JimB]

Getting the bends from swimming?
I dont think so.
The bends is for divers, it is caused by nitrogen dissolved in the blood "boiling off" as the pressure is reduced as the diver returns to the surface.
The cure for bends is to re-pressurise the diver, and then bring him back to atmospheric pressure slowly.

As for electric fields etc, my personal opinions:
Being in close proximity (>10m) to a cellphone base station, thats OK.
Holding a cellphone to my ear for extended periods (>5mins), I try to avoid it.
Living under or near (<100m) high voltage power lines, no way Jose.

JimB

 

[RadioRon]

Yeah, I guess I used the wrong term when I said the "bends". I really meant to refer to debilitating cramps.

 

[JimB]

All those RF fields are driving you round the bend.

JimB

 

[Zener_Diode]

thanks, now I understand.

 

[Hero999]

Human body not big enough to act as an antenna?

At 1Hz to 4Hz (the frequency of human brainwaves) no, at higher frequencies yes, but the only scientifically proven hazard is the heating effect, which I'm, told only needs to bve <0.1 degrees C to effect sensitive areas like the brain.

Why do people get struck by lightning then?

Because we're conductive and are a shorter rout to ground in an open field.

Apparently electromagnetic waves do polarize your brain juices. Didn't you learn that in your electromagnetics class? Whether it is enough to concern you or not is up to you.

I've heard that there is some evidence that very strong steady DC magnetic feilds do have an effect on the brain but there isn't any to suggest that this also occurs at powerline frequencies.

Living under or near (<100m) high voltage power lines, no way Jose.

Interesting because there is some evidence to suggest that whilst the electric feilds aren't directly harmful their effect on airborne particles is. The high voltage fields ionise polutants causeing chemical reactions and producing more harmful compounds, they also create ozone which is toxic.

So yes I agree power lines aren't good, perhapps they should put more of them underground.