Alarms + Pagers

[Guest TerryBarry]

Gentlemen,

1km = 1000 metres

100 metres = 0.1 km

Therefore 0.1 x 0.1 km = 0.01 sq km

 

Terry

[Guest Guy]

I think you are being cought out by the squair rule,

 

There are 1 million squair meters in a Km, so 10,000 m2 is 0.01km.

 

Think of it another way, 0.1km * 0.1km = 0.01km2.

 

Ah I see that Terry beat me to it

[Guest Andy Rathbone]

squares are all well and good but radio travels in circles, so wouldnt it be a 100m radius?? which would be a 200m diameter circle?? just to add a little fuel to the heat of the discussion

[Guest Stuart Ainslie]

Best idea - stuff the mobile phone and buy a Tracker then! !

[Guest TerryBarry]

Andy,

Surely radio waves travel (as a first approximation) in a straight line.

Therefore they will propagate from a point source to cover a circular area.

So are we looking for a circle bounded by a 100 metre square or a circle of 100 metre radius - there's a big difference.

But does it matter?

Hey Ho - off to work

 

Terry

[Guest Guy]

Okey hear we go,

 

the 100m will be the tollerance in front or behind the phone with respect to the perticular base station that is being used to locate it, this will give a circle round the base station of a particular distance +- 100m.

 

A second base station will do a simalar thing and your phone will be in a space where the circles cross, imagine drawing two circles with a cumpus and a fat marker pen.

 

your phone could now be in two places so you need a third base station to select which one.

 

The tolarance of the phone system and the GPS is given as +-100m for political reasons but the actual tolerance is around +-1m.

[Guest Roger 2B]

aa

[Guest Andy Rathbone]

now we know who works with or in the telecomms industries as well,

your propagation patterns also depend on the shape of your aerial, but to be honest it doesnt realy matter, just get a traker if your worried about it being stolen and large bear traps to place on the seats to stop the local youffs trying it out, a taizer steering wheel would work well to

[Guest daveg]

All

 

Ok, we're all wrong including me

 

Radio wave's actually don't travel in a straight line, they are bent by gravity...Einstein's general theory of relativity...

 

If we are looking for a phone thats 100 meters from a base station, it could be anywhere within a 200 metre sphere

 

So, 100 x 100 x 100 x pi x 4/3 = 4.2 million sq metres

 

Now find the phone

 

Dave

[Guest Andy Rathbone]

Radio wave's actually don't travel in a straight line, they are bent by gravity...Einstein's general theory of relativity

but not all radio waves, else how would we speak to astronaughts on the moon? some bounce off the ionosphere (generaly termed sky waves) which is determined by the sun and the solar wind, some escape throught the ionesphere, hence the ability to talk to the moon, and how GPS satalites can send their signals back down, because if satalites couldnt send signals back to earth or us send control signals to them, the whole telecomms network inc landlines wouldnt work quite as well as it does at the moment. trust me

but what this has to do with the original thread is completely achademic,as you can tell i'm not from my poor speellling

[Guest daveg]

Andy

 

What you are talking about is Quantum Electro Dynamics...

 

This covers reflections etc...

 

Got to go...can't seem to find my mobile...

 

Dave

[Guest ian luxford]

sounds like a great offer though...

nick a hood get a mobilephone free!!

be very peed off if they left the car though!

[IanS]

The 100meters accuracy makes a big assumption.

The assumption is perfect propogation of the radiowaves.

Hills buildings etc tend to mess with this assumption.

The base stations hand over depending on signal strength and in the hills when tracking has been tried some wierd results have come in with the strongest signal from base stations a considerable distance further away.

The direction finding capability of the admitedly 5 year old ones that I was involved with was normally only good to about +-30deg.

Base station spaceing ranges from about every 400meters to 20kms.