I made some measurements using a scope coupled to the line with a X10 XPCP passive coupler.
The unit transmits all three signal bursts. Totally unloaded it delivers 30Vpp on phase 1 and phase 2, and 15-20Vpp on phase 3. Apparently the power supply is running out of energy for the third signal burst.
Then I plugged a X10 Maxi Controller into the same circuit to add some loading. Phase 1 and phase 2 fell to 21Vpp, but there was little change in the third signal burst.
Since just adding a Maxi Controller to the circuit decreased the amplitude by 30%, it may be limited in how much power it can deliver. The 120KHz waveform was not a clean sine wave as it is for the Maxi Controller.
Follow-up: I tested with a 5 ohm resistive load, which is in the X10 spec, and it delivered 15Vpp. The X10 spec is 5Vpp minimum into a 5 ohm load, so it is doing much better than the spec. And with a 5 ohm load it delivered a clean sine wave.
Jeff