How Do (Mobile) Telephones Work?

Samtheman1k · 14 Jul 2006 at 09:20

Psyk said:
Electrons actually travel extremely slowly down a wire, usually only a fem mm/s. But of course what matters is that when they start moving it pushes the one in front of it (I'm sure it's more complicated than that, but that's the jist of it) so you get the effect very quickly (although probably not the speed of light).

I found this quite strange when I did it in physics. You imagine electrons speeding through wires when really they are moving very slowly (in the direction you want them to go anyway).

It's not that strange really. It is just like water in a pipe.

Samtheman1k · 14 Jul 2006 at 09:23

Oracle said:
Satellites
PPFT! yeah right, we wish!

Its POS (Point of Sight) and they operate at 2.4gHz same as a microwave oven and 802.xx wireless. (cooking your ear tbh!)

If the repeater (mast) cant see your phone, it aint gonna work, similar to a TV, they use plain old Radio waves. Satellites arent involved (unless maybe calling abroad!)

I'm not sure if this is a joke or not. Mobiles (2G) use either 900 or 1800MHz, or 1900 in the USA (as they like to be different).

Borris · 14 Jul 2006 at 10:55

Samtheman1k said:
It's not that strange really. It is just like water in a pipe.

Not really - You don't rely on the flow of electrons for power, but the flow of the energy from those electrons.

Think of one a newtonian cradle (the metal balls on sting executive toy) - Imagine there are millions of the little things in a room. I hold one, at one end, and shake it back and forth, transmitting the jiggly motion, which is, in turn, picked up at t'other end.

I call the force needed to do the jiggliing Borridays, shorted to B.

You may call them Volts if you wish.

Samtheman1k · 14 Jul 2006 at 10:58

I guess that depends on whether it is DC or AC.

Borris · 14 Jul 2006 at 11:06

Samtheman1k said:
I guess that depends on whether it is DC or AC.

The same holds true.

Unless it's AC/DC, in which case it goes both ways.

Oracle · 14 Jul 2006 at 11:07

Samtheman1k said:
I'm not sure if this is a joke or not. Mobiles (2G) use either 900 or 1800MHz, or 1900 in the USA (as they like to be different).

My bad, what I meant was that GSM phones operate at 1800mhz but by comparison to a 2450mhz microwave, can emit 3.2 mW/cm² at 2".......a microwave only kicks out 1 mW/cm² at 2".............although i don't know why this is relevant so................................meh!

Samtheman1k · 14 Jul 2006 at 11:11

Borris said:
The same holds true.

Unless it's AC/DC, in which case it goes both ways.

I'm sorry, I don't understand what you are saying, are you saying that there is no such thing as the net [drift] flow of electrons in a DC current?

Borris · 14 Jul 2006 at 11:15

Samtheman1k said:
I'm sorry, I don't understand what you are saying, are you saying that there is no such thing as the net [drift] flow of electrons in a DC current?

Not at all - Just that the juice coming out at the other end is the jiggling, not the flow.

The AC/DC comment is a play on the fact that AC/DC is also a euphemism for bisexuality.

Samtheman1k · 14 Jul 2006 at 11:26

Borris said:
Not at all - Just that the juice coming out at the other end is the jiggling, not the flow.

But I thought that electric current was the flow of charge, not 'jiggling'?

Borris · 14 Jul 2006 at 11:51

Samtheman1k said:
But I thought that electric current was the flow of charge, not 'jiggling'?

My bad - The jiggling is the signal, not the charge.

Go about your business, nothing to see here.

Dave · 14 Jul 2006 at 12:13

vonhelmet said:
Speed of light = fast.

Not according to the Americans:

Samtheman1k · 14 Jul 2006 at 12:22

Dave said:
Not according to the Americans:

Quality find.

Le_Petit_Lapin · 14 Jul 2006 at 12:29

Borris said:
38 miles per hour is not fast.

Damn...if we cant go faster than the speed of light, then in your wee universe motorways must utterly suck to drive on.

Borris · 14 Jul 2006 at 12:34

Le_Petit_Lapin said:
Damn...if we cant go faster than the speed of light, then in your wee universe motorways must utterly suck to drive on.

We can travel much faster that the speed of light though.

Much, much faster.

Bear · 14 Jul 2006 at 13:52

Oracle said:
Its POS (Point of Sight) and they operate at 2.4gHz same as a microwave oven and 802.xx wireless. (cooking your ear tbh!)

If the repeater (mast) cant see your phone, it aint gonna work, similar to a TV, they use plain old Radio waves. Satellites arent involved (unless maybe calling abroad!)

Its called line of sight and mobiles dont need line of sight to work as it can use reflections of propagation, in fact using antenna diversity enables multiple propagation paths so the mobile can pick up multiple instances of the same signal.

GSM 800 mobiles use the 800MHz and are used by operators like O2 and Vodaphone band and opertaors like Orange and T Mobile use 1800MHz sometimes called PCN.

edit: Just read your correction

Bear · 14 Jul 2006 at 14:10

Stelly said:
I thought there was a reason it was called a CELLULAR network

Stelly

It is, each base station constitutes a cell. With in each cell there are a certain amount of channels (200kHz frequency bands) available depending on the operators allocation. Each of those frequency bands in GSM can allow 8 people to talk at the same time using a scheme called TDMA (time divison multiple access), so when you are talking to someone on your mobile, there are also another 7 users on that frequency.

Now you have all that frequency allocation, which is obviously finite. To get round that, cells are created where "x" amount of the frequency is allocated to that cell and neighbouring cells will use another "x" allocation which is different. Only where the cell isnt neighbouring, you can reuse the frequencies (frequency reuse) so you can have more users than the frequencies that are available.

Also frequencies arent reused on neighbouring cells because if you have a certain frequency allocation when on the phone, if you're moving ie in a train etc, then if someone is using that frequency when you cross into that cell, it might cause problems due to the clash of frequency use.