You might be interested in this application note http://www.national.com/an/AN/AN-146.pdf
Your neighbour may be able to hear your transmission if they are using a cable that´s connected electrically to the same phase you are using for the transmission
Ofcourse they would have to know you are using such a transmitter and they would also have to figure out your carriers frequency (not difficult). And I guess they would have to be close, since the signal wont go that far (I would say some 100 meters or so depending on how strong a signal you're transmitting)
For stereo you would use two carriers one for each channel.
Hm, come to think of it, I might try building one, for my background music, when time allows
Your neighbour may be able to hear your transmission if they are using a cable that´s connected electrically to the same phase you are using for the transmission
Ofcourse they would have to know you are using such a transmitter and they would also have to figure out your carriers frequency (not difficult). And I guess they would have to be close, since the signal wont go that far (I would say some 100 meters or so depending on how strong a signal you're transmitting)For stereo you would use two carriers one for each channel.
Hm, come to think of it, I might try building one, for my background music, when time allows
Drafance007 said:Wow, the reciver is not very simple...does it need to be so complicated....what does all that components do there?
Well actually it is not entirely unlike a FM receiver.... Actually what you do is add a modulated signal, in this case FM, to the power cable. The receiver is nothing more than a tuned transformer and an FM receiver with a fixed frequency. The tuned transformer works like a bandpass filter so that the receiver only sees the signal your sending (not the 50/60 hz power signal). The rest of the circuit demodulates (i.e. moves down the audio signal to audio frequency) and amplifies it.
Reading from the schematics of the transmitter: T2, D2, D3 is the power supply/rectifier and LM78, C6, C9 is the regulator for the power supply.
The source is connected thru R7 and R8. Notice that you need two circuits if you want to build a stereo transmitter (If you want stereo you will have to send two FM signal each with its own carrier frequency). R1 is there to adjust the input signal level.
LM566 is a Voltage Controlled Oscillator (VCO). This transforms the audio signal to a FM square wave. The carrier frequency is set by C4 and R4.
Q1 amplifies the square wave, which is then sent thru T1, a tuned transformer (so that no pesky AC enters the circuit).
Reading from the schematics of the receiver: Again the same power supply. The signal is taken for the tuned T1 (R1 is there to avoid ringing when noise spikes occurs). Q1a-Q1d takes the distorted signal and amplifies it to a square wave that (hopefully) is the very similar to the transmitted one.
LM566 is the phase locked loop (PLL) that is used as the FM demodulator. The frequency is set by R16 and C13. R15, C11 and C12 help the PLL to lock on the carrier frequency even if it varies. D1, Q2, C6, C7, Q1e and R10-R12 form a mute circuit. Q1E is biased when there is no carrier and shorts the signal to ground.
The LM308 is a small amp (2,5W into 8 ohms) that could be replaced if more power is needed. In fact most of the circuit could be replaced
The principle is anyhow to modulate the audio (or whatever) signal and then send it thru a tuned transformer into the power line, then pick it up with another tuned transformer and then demodulate and amplify...
Hi guys, just a few safety notes! 
Playing with mains power is potentially dangerous, you should be aware of the risks at all times.
If you make something like this, you need to be able to physically unplug it, and so it should be not directly wired into the mains.
C1 and C2 shown in the schema above need to be X or Y rated mains caps, or they will blow up!
finished!
However apart from the safety stuff I have to mention, I know that places like Early Learning Centre sell these sort of things as baby alarms, and for about £10 GB- by the time you had had made the custom traffos, and worked out and built a prototype, I think it would cost much more than this!
So, carry on as a thought experiment, but for the price, go for a ready made one
Playing with mains power is potentially dangerous, you should be aware of the risks at all times.
If you make something like this, you need to be able to physically unplug it, and so it should be not directly wired into the mains.
C1 and C2 shown in the schema above need to be X or Y rated mains caps, or they will blow up!
finished! However apart from the safety stuff I have to mention, I know that places like Early Learning Centre sell these sort of things as baby alarms, and for about £10 GB- by the time you had had made the custom traffos, and worked out and built a prototype, I think it would cost much more than this!
So, carry on as a thought experiment, but for the price, go for a ready made one
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