110902-1040 EDT
Back to my original discussion. Since that point I have learned a great deal more about the TED system.
Some definitions first:
PLC is a name (acronym) for power line communication. This uses a high frequency carrier to transmit data over conventional 120 V power wires in a home or building. TED uses 132 kHz, X10 uses 120 kHz, and others may be at different frequencies. Then there are various devices using the power system that may introduce noise into these frequency bands. Also there are loads that attenuate the signal level.
FILTER generally means to remove or separate. From dictionary.com for electronics the definition is:
"6. Electronics, Physics . a circuit or device that passes certain frequencies and blocks others."
SIGNAL to NOISE ratio (S/N). How strong a desired signal (signal) is relative unwanted signals or random noise (noise). The higher this ratio the greater is the probability of correcting detecting and extracting data from the desired signal. This ratio can be improved by increasing the transmitting power, filtering to reduce excess noise, reducing noise at the source, and better detection means, such as correlation detection.
Starting with X10 type systems. This system concept is based on the ability to have many different transmitting locations within the power distribution system of a building, and to have many different distributed receiving locations. This has to be viewed as a big network of parallel wires onto which a signal is injected somewhere (transmitted), and that can be received anywhere else. This has major problems from two sources --- shunting loads that attenuate the transmitted signal, and noise generators.
I believe the TED 1000 system started out with the X10 concept that would allow the MTU to be located at the main panel, and then the RDU could be plugged into any outlet for viewing data. This flexibility and no wire installation were selling points. From a marketing point of view seems to make sense. But from a technical view it is unreliable.
Problems were discovered. Namely errors or the system did not work. Thus, in each individual case patchwork solutions are suggested. Experimentation is required and somewhat indirect means are used to see if an improvement occurs. In many cases I suspect that operation may be marginal. Why should a receipt of 20 % bad packets be considered acceptable?
One of the solutions is filters. This is good as a starter. But more tha that should be done.
What is being called a filter I would rather call a filter-isolator to be more descriptive. The word filter being used to mean high attenuation of unwanted signals from the input side of the filter to the output side. This would reduce noise or other signals on the output side of the filter for the TED components of interest on the output side from the noise and other signals that originate on the input side of the filter. This I could do nicely with a cascaded sequence of L-C low pass filter stages. Series inductance and shunt capacitance. But this would be bad for the TED system on the output side because of the last capacitor in the filter. This capacitor looks like a short to the TED transmitter at its carrier frequency. A short to the transmitter lowers its output signal, thus reducing the S/N at the receiver.
So a filter alone is not the solution. At the filter output there needs to be a high output impedance at the TED carrier frequency. Now the TED transmitter won't be heavily load and its signal level will be large. To distinguish the required filter device from an ordinary Corcom filter, such as a 5VR1, I would prefer to call the TED filter a "filter-isolator". I might point out that I have probably 20 or more filters like the 5VR1 scatter through my house. These are on all my fluorescent fixtures to reduce radio noise from the lights.
Note: the filters supplied by TED are X10 filters and these are a "filter-isolator, and do a reasonably good job such that if the TED setup is as I describe next it should perform in a rock solid fashion relative to S/N.
The way to solve the power line communication problem is:
1. Erase the concept that any circuit in the house can be used for for this PLC. Means there is going to be a dedicated circuit for each Gateway or RDU and nothing else is on the circuit.
2. An in-line filter-isolator is installed at the main panel. There is no choice, you use the in-line filter-isolator. If the Gateway uses the red input wire, then a second in-line filter-isolator is required. Again, no choice it must be used.
3. This will be classified as an isolated circuit. There must be nothing else connected to this circuit, except 1 Gateway, and up to 4 MTUs that are associated with this Gateway.
4. Following this approach there should be rock solid communication with no communication problems if all the components are good. I expect bad packets to be essentially 0.
An experiment I ran earlier today with a plug-in filter-isolator as the filter and only a 5000 Gateway and 1 MTU produced a good signal. Adding a resistive load, a 1500 W heater at low power, 735 W (6.13 A at 120 V 19.6 ohms), reduced the signal level to 2/3. Without the in-line filter-isolator, in a normal house with large electrical loads, there could be far more attenuation of the transmitted signal than with the low power heater. That the in-line filter-isolator provides a series high impedance at 132 kHz is why its use prevents loading down of the transmitter from shunt loads on the input side of the filter
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