well it is going to be a rather cold swimming pool. Even when ringing you won't get more than a few watts out of a phone line.
Ahh! But that's where the transformer comes in - I'm surprised you missed that.
Ok, some basic electrics for those who don't understand what I'm talking about... I'll try and make is as simple as I can. Plugwash, don't worry if you don't follow, I'm happy to explain as many times as I have to
Ok, transformers as we all know can step voltage up or down, or step current up or down? Right? I think we are all agreed on that.
To get a higer voltage from a transformer you just have more turns on the secondary than the primary, the ratio of turns gives the voltage ratio. To get more current out, you need thicker cable on the secondary.
So in laymans (really basic) terms, more turns means step up the voltage, thicker wire means more current.
If it helps just think about a cars ignition coil - lots of thin wire = step up voltage. Then think of an arc welder - a little thick wire = step up current.
Now , here is the really clever bit that no one ever thought of (except me) Just use lots of turns
AND thick wire. Then you get the best of both worlds, you can have your cake
AND eat it. You get voltage step up and current step up. This of course means that you get
MORE power out.
(Power is roughly equal to current times voltage)
Now, the reason most people don't do this is that it's a very tight squeeze to get lots of turns of thick wire on your transformer, but just get a big one, don't be stingy! REMEMBER you'll get loads more power out than you put in!!! and of course the electric is from a phone line, or ISDN or ADSL so is free anyway!! So get a big transformer - RF's idea of an old site 55-0-55v transformer is a good one, you just need to rewind it a bit.
Ok, if you are still following (sorry if it's a bit techie) here is the maths.
Say we've got 60v on our phone line, so we'll need 4 times that on the secondary to bump up the voltage. So 1000 on the primary, so we put about 4000 on the secondary (I use 3998 normally, to give just under 240v) Now the current - you probably have 100mA on the phone line, now my mate's pool heater is 15Kw which is about 60Amps so we need a roughly 600 times step up on the current.
No worries! Just use wire on the secondary that is 600 times thicker than the primary.
Ok, I admit, this seems tricky, but we can always use thinner stuff and parallel it up, I usually use no thicker than 10mm^2 as it gets hard to work with. Keep your windings tidy and you should
just about get it all in.
...and just when you thought this was all too good to be true... it gets even better!! Transformers are big old electro-magnets, we can squeeze a bit more power out if we place big conventional magnets around the outside of the transformer just stuck to the E or I laminations - it just gives you that bit more ooomph. As a rough guide some of the big magnets of a loudspeaker should give an extra 5amps or maybe 8 at a push if you are really good at placing them on the flux lines.
The analog signals to and from your phone only have to make it as far as the local exchange. From there onwards it is digitised and sent over what is essentially a data network.
No, they don't, at least not where I live, Maybe it won't work round your way where it is digital, that's a shame. But between 1-94% of people still live in an analogue area, and you can sometimes dial a prefix to get the call routed over the old legacy network anyway.