Most X-10 transmissions are less than 1 volt in strength.
Actually, most transmissions are between 4 and 6 volts (some even as large as 10 V). If the module is a long way from the transmitter (electrically) it will probably be less than 1 volt though.
Such things as computers, surge suppressors, TV's and many other devices may cause excess noise.
He is confusing power line noise and signal attenuation. This is easy to do since both result in the same problem and a noise filter can fix both problems.
If two signals are transmitted at the same time, they will collide and no action will take place. This is only true if the signal is on a different code. If the signal is on the some code, a feature in the X-10 receiver will ignore the repeated signal. This circuitry is needed in order to allow the amplified couplers/repeaters to function.
This is sort of but not really right. There is no special circuitry to do this. It is more like if two people say exactly the same thing at exactly the same time you can easily understand what they are saying, but if they are saying different things or if their timing is off, it is difficult to understand what either one is saying.
Couplers and Amplifiers (The heart of the system)
A coupler/repeater is not an amplifier. It is a repeater. It is kind of like when someone asks a lecturer a question and he repeats it to make sure that everyone heard it. You can also get amplifiers for x10 (such as SmartHome's BoosterLinc), but you have to be very careful when using them as they will amplify both the noise and the signal, and if they are too close to the transmitter, they can actually make the signal weaker.
The problem with the passive, or non-amplified coupler is it has to cut the signal in order to cross it over to the other phase of voltage.
This isn't totally true either. Typically there is only a slight reduction in signal strength when you use a passive coupler. The probelm occurs if there is something which produces a lot of noise at the same frequency as the X10 signal on one phase, the coupler will couple that noise to the other phase spreading the problem throughout the house.
Most of today's electronics have “clean” power supplies in them. In order for them to be clean, they must put the garbage, or noise, somewhere. This noise is reintroduced into the power lines of your home.
This isn't true either. Most "clean" power supplies don't put the noise back onto the powerline, but instead absorb (trap) it. The problem is that they will also absorb the X10 signal.
There are two easy to find filters available. One is rated at 5 amps and the other is rated for 15 amps. The 5 amp is a plug in style while the 15 amp is an in line model.
These days there are many filters available. You can get 5, 10 and 15 amp plug-in filters and 15 and 20 amp in-line filters. You can also get noise traps which don't trap the X10 signal. They don't have a current rating, but if the noise is too close to the X10 frequency, it won't be filtered.
I know I am splitting hairs here, but I like to make sure that the information on this forum is accurate.