Cell phone towers

And they'd probably get around the issues by delivering the longish-haul with lasers and using magnetic induction to complete the "last mile" so to speak
 
sn3rd said:
Interesting stuff in that wiki article about just this... More focused than you'd think. Even laser beams (whether through fibre or otherwise). Great stuff!!
Click to expand...

One of my more memorable achievements as a school-kid was to build a CO2 LASER that would shatter glass at a ERP of 10 watts!.

So I'm not going to beam a few hundred watts around my house if I can potentially break the beam with my body. (Visions of light sabers :eek:)
 
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Wow... Geek childhood of the year award goes to... :p
OK, you win... ;)
Still, engineers will make it work. If they can attempt communication with parallel universes using gravitons, they can provide safe, efficient wireless power
 
sn3rd said:
And they'd probably get around the issues by delivering the longish-haul with lasers and using magnetic induction to complete the "last mile" so to speak
Click to expand...

As long as it's wireless, it must pass through air. And that creates the potential for a living creature to ingress the space occupied by the beam, be it a bird or a human.

At the power levels we use for communications (a watt or two) it's not an issue. But if we're going to power equipment, this can raise to kilowatts and that's a completely different matter.
 
I get that, but more than likely, a solution will be found, whether it be by some completely different medium (teleportation) or by using very focussed, directed beams... I have faith in the human race to make the impossible possible
 
sn3rd said:
Wow... Geek childhood of the year award goes to... :p
OK, you win... ;)
Still, engineers will make it work. If they can attempt communication with parallel universes using gravitons, they can provide safe, efficient wireless power
Click to expand...

:) Must say, it was quite cool, building you own 'death-ray' when it was just the stuff of science fiction. I'm talking 1980 here.

Not sure how you'll get so much power across at low levels. Maybe massive spread-spectrum? But the total amount of ERP must stay the same, conservation of energy, you know.
 
Massive spread spectrum wouldn't solve the issue of efficiency, so it'd probably make the technology debilitatingly expensive
 
Damn this thread has turned geeky! ;)

Just a question... V3G you mention that communications use low power levels and are therefore not a problem but if these levels were increased it could pose a danger.

Now my question is one phone, or one antenna on a one tower, may use a few watts but what is the effect of thousands of these in an area? Is the effective output of these "added" together creating the effect of a higher output? Or does it not work like that?

Do these waves "float" around us or are they very directional and go directly from the phone to the antenna?
 
Er... to hijack the question directed at v3g, a bit of both, really. As has been mentioned quite a few times, smaller wavelength and higher power is what makes the waves more dangerous. Adding an extra tower would be like adding an extra cup of water to the sea. You are constantly bombarded with electromagnetic signals from the minute you're born! Light, radio (as in Jacaranda. Highveld, etc), satellite, wifi, OTHER cellphone towers...
 
The list is endless...

The signals are often at different frequencies and frequently out of phase (see wiki article on constructive and destructive interference). The human body isn't a great antenna. The issues arise when the signals start off at very high levels (as in the case of wireless power transfer)
 
LancelotSA said:
Damn this thread has turned geeky! ;)

Just a question... V3G you mention that communications use low power levels and are therefore not a problem but if these levels were increased it could pose a danger.

Now my question is one phone, or one antenna on a one tower, may use a few watts but what is the effect of thousands of these in an area? Is the effective output of these "added" together creating the effect of a higher output? Or does it not work like that?

Do these waves "float" around us or are they very directional and go directly from the phone to the antenna?
Click to expand...

Best way to think about this is to try and visualise this as follows:

But firstly, all electro-magnetic radiation is the same, it's just the frequency that differs. This is important to remember.

Human eyes are sensitive to a specific range of quite high frequencies ( around 5*10^14Hz, that's about 5 000 000 GHz!) and we arbitrarily call this 'light'. We can see from about 4*10^14 Hz (which we call 'red') to nearly 8*10^14 Hz (which we call 'blue').

At a MUCH lower frequency we have what we call 'radio waves' (88 - 108MHz for commercial radio, etc.), 'micro waves' is typically from about 3GHz upwards but commercial microwave ovens transmit 2.4GHz. (As does WiFi, Bluetooth, DECT, Zigbee, and many other systems). These we can't see but that's only because the rods and cones in our eyes are not sensitive to them.

So there is NO difference between radio and light waves. The same rules apply to both of them. They're just different frequencies.

Now lets say your eyes were sensitive to radio frequencies. If you had to look out over the city, you would see each each radio transmitter as a light bulb, glowing and radiating outwards.

The stronger the transmitter, the 'brighter' the light. As a rough indication a SABC TV transmitter would look like an aircraft search light (100KW) , while a cell tower would look like a street light (10W) and a mobile phone probably like a handheld torch (2W). You'd see every WiFi access point, bluetooth transmitter, etc. although faintly. If you had to look inside your PC, you'd see a soft glow around your CPU and the 'colour' of the glow would indicate it's speed!

BTW, your cell phone would not radiate all the time, mostly only when you talk.

The shape of the light pattern around the radio transmitter would be determined by its the antenna.

A radio transmitter that must serve all people around it could have a globe of light around it, just like a normal light bulb, but more likely it will look a bit like a pancake, round and equidistant in the horisontal plane but quite flat. This saves wasted energy as typically people are in the same plane as the transmitter. (This is why you often get a poor signal directly UNDER the transmitter.)

A point-to-point radio link (like a Micro-wave or WiFi transmission link) will be more like a spotlight. Still the same light source, but now the transmitter has a parabolic dish or antenna, so the beam is formed to be directed at a small target. Just like a torch, it now can be seen further, but only in one direction.

So, looking out over an area with many radio transmitters, it will appear just like looking at the city lights at night. There will be many lights, of different brightness and patterns.

Just to complete the analogy, sometimes you're so far away from the source of light that it's not very visible. To then see it better, you use binoculars or a telescope. This grabs a lot of the radiated light and force it onto a small space (your eye). You know see a 'amplified' picture.

This is exactly what a high-gain antenna does for your data card, it acts like a telescope and allows you to pick up a signal that was previously too weak.

OK, now to answer your questions above, although I think you can probably figure them out now :)

All these light sources transmit 'light' and based on the strength of the light-globe or the shape of their respective lenses they will appear to be brighter or dimmer depending where you stand in relation to them. If you're right next to a light-house and you look straight into the beam, your eyes are gone. But if you're 20Km's away from the same light-house or you're behind the lens, you'll battle to see it.

Once the light has left the source it's being absorbed by many things and it ceases to exist very quickly. So it does not float around for ever. Just think if the light radiated by the sun never got absorbed. Every day the ambient light on earth would get brighter and brighter till eventually we would have no more day or night!.

So just like light levels drop very quickly as you move away from the source, so does radio waves (remember they're exactly the same thing).

If you're under a light source that has a special lens to throw the light sideways but not up or down (like the cell tower on your building), again the light that 'leaks' down will be very little. On top of the building, right in front of the antenna it will be the brightest.

But it might or might not be bright enough to hurt you. For sure if it's a massive spotlight, you're going to get hurt but if it's a lower power light, you'll handle it. (Heard of the Darwin-award winner who used to go and sit right in front of a massive microwave transmitter as it made him warm?)

So this is the crux of the whole discussion. The "harmfulness" of a transmitter is a factor of a few things:

1) The frequency - lower is better. Cosmic rays at 10^22Hz will kill you.
2) The ERP (Effective Radiated Power) - The combination of the raw transmitter power + gain the antenna gives it.
3) Your position relative to the radiation. If it goes over your head, you won't see it.
4) Your distance from the source - it drops rapidly with distance and the drop is non-linear, i.e. it drops quicker the further you move away. This is why you all complain about 3G coverage!. Sometimes a 3G tower can only reach a few hundred meters. Also, the higher the frequency the quicker the drop. That why we need more 3G than 2G towers for the same coverage.
5) Your ability to absorb it - Again, higher is more problematic. You don't want to hang around an X-ray machine (3x10^18Hz) all day.

All these factors together make it so difficult to figure out what a 'safe' dosage is. We know the general rules and effects of frequency and power (lower is better), but studies are still trying to figure out the exact details. But up to now, the general consensus is that the amount of power transmitted by mobile systems are within the safe side.

So remember to think of radio transmitters as light sources, it's 100% accurate and it give you a nice way to visualise all the signals flowing around you! If you want to play it safe avoid the bright spots!
 
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Isn't true that in South Africa it is only the IR, Intentional Radiator (aka everything before the antenna) is governed.

Not the EIRP (Effective Isotropically Radiated Power) unlike overseas. If that is true then one would be able to attach any type of antenna (to ensure high gain)
 
This might be a litlle off topic but I have a big yard and bad reception, I know alot of people in my nieghbourhood complaing about vodacom signals so how do I give them a offer to come put up a tower in my back yard. Sorry if this is a little off topic but I didn't want to start a new thread for this one question.
 
Its in durban. They wanted to put a tower up but they couldn't find a host but i'd host it for them. . . I have ample yard space
 
Linoman said:
Isn't true that in South Africa it is only the IR, Intentional Radiator (aka everything before the antenna) is governed.

Not the EIRP (Effective Isotropically Radiated Power) unlike overseas. If that is true then one would be able to attach any type of antenna (to ensure high gain)
Click to expand...

Don't know, to be honest, I'll ask.
 
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