Re: geography nerds?

In article <20080222.1630.108835snz@[EMAIL PROTECTED]
>,
dbell@[EMAIL PROTECTED]
 ("David G. Bell") wrote:

> Part 1: When a mobile phone is switched on, it has to get through 
> an exchange of signals with the network, to let the network know 
> where it is, and to find the best two-way signal. So that 
> stuttering noise is the phone transmitting. And the phone has to 
> do some transmitting to let the network know where it is when a 
> call comes in.
> 

And, presumably on a train journey, it has to send out to re-establish
the link as you go through cells.


> Part 2: The iPod is a small computer and an audio amplifier. If 
> it doesn't actually crash, the frequencies used by the cellphone, 
> and the radiated signal, probably isn't messing with the computer 
> side. But there's a general audio problem when you expose an 
> audio circuit to a strong radio signal. If there's a diode 
> somewhere in the circuit (or a lot of other components with the 
> same effect) the induced AC from the radio signal becomes a lot 
> of pulses, of varying strength. Because the circuits lose the 
> radio frequencies--headphones will do this--the signal is sort of 
> blurred, and you hear any audio frequency element.
> 
> This is, incidentally, how a crystal set works. A very strong 
> radio signal (helped by a long aerial), a diode as detector (the 
> original crystal), and the headphones which only responded to the 
> audio. Oh, an a tuned circuit so you could listen to a particular 
> transmitter.

At university, I had a friend who built his own amplifier for his hi-fi.
When he switched it off, the speakers gave out a strange wooo sound
lowering in pitch.  (I realise now it sounded a bit like a theremin.)

What was strange was that he had the room above mine in the hall of
residence we lived in, and when he switched his amplifier off, I got
exactly the same sound coming out of my record player.