Several customers have reported X10 commands being decoded with 0.00V signal levels. This has been puzzling because I had never seen an X10 signal level that low in my testing. I was able to recreate that today, and those readings appear to be valid. Essentially, it means the signal level is below 10mVpp.
First I read the output from a Maxi controller directly, and then through an XPPF filter. The levels were 6.64V and 0.16V respectively. So that shows the filter is reducing the signal level by about 97%,
Then I read my test signal, which is on the other phase from my isolated lab test phase. That read just 0.06V, which is the signal that I use to test the repeater function in all XTB-IIRs. Then I read that signal through the XPPF, and the XTBM-Pro was still able to decode it with a 0.00V signal level. If that 97% reduction holds up at that low level, the signal would have been only about 2mV. I think it is safe to say that the signal would be below .01V, and hence the .00V reading.
I had never seen the XTBM or XTBM-Pro decode a signal that low because my powerline noise runs .01V to .02V. Connecting the XTBM-Pro through a filter reduced both the noise and signal level, and showed what the XTBM can really do in a very low noise environment.