TED power line communication is a moderately steady data stream. X-10 and similar devices are very intermittent.
TED 1000 outputs a stream (packet) of data about 0.1 second long, and this occurs every 1 second. Thus, a single TED MTU is consuming 10% of the channel capacity. One packet extends over about 6 cycles of the 60 Hz supply. There is only one way communication in the TED 1000 system for normal data collection.
TED 5000 outputs a stream of data about 0.2 seconds long, and this occurs every 2 to 5 seconds. Again for a single MTU it may be about 10% of the channel capacity. In addition every 1 minute a longer packet is sent that requires an acknowledgement from the receiving end.
In the TED system a lot of data is sent in 1 second. In the X-10 system one on or off command can be sent in about 1 second. For most applications the TED data only needs to go to one location to do an adequate job. In the X-10 application the command must go to many dispersed locations in a broadcast fashion. TED really does not need to operate in a broadcast type mode. However, TED is sold with that capability as a feature.
If I was designing a TED system I would use a dedicated wired connection. Too many customers are tolerant of computers and other electronic devices with bugs and other types of problems. PLC (power line communication) appears, from the comments on the Internet, to cause a lot of problems for TED customers.
A TED system operates at a 125 kHz carrier frequency. This is about the 7500th harmonic of 60 Hz. Unless you employed a very good square-wave shaping circuit on the basic 60 Hz sine wave there would be little energy at 125 kHz. There may be devices connected to the AC line and synchronized to 60 Hz that generate substantial power in the 125 kHz range, but I don't really want to call these harmonics. Rather I would consider them as uncorrelated noise.
What is a good reliable method to work with the TED system, and also prevent it from interfering with other systems? Select an existing 120 V branch circuit, or create a new circuit. This is to be an isolated circuit with only one RDU xor Gateway and the associated MTUs as the connections to the isolated branch circuit. Where this isolated circuit connects into the main panel place an X-10 in-line filter between the breaker and the isolated circuit. The in-line filter places a high impedance at around 125 kHz between the isolated circuit and all other circuits.
With this scheme I can get zero packet errors over very long time periods. No problem over a 250 ft length of #14 Romex cable.
You can find additional information at my web site http://beta-a2.com/ . Pick Energy for a summary of my book ( http://beta-a2.com/energy.html ), and pick TED MTU Data Format for a discussion on the 1000 and 5000 packet structures.