Another status update on the signal meter (revised 7/24): As mentioned earlier, I incorporated a hardware mod to be able to measure the carrier frequency. I updated the prototype photo showing that readout:http://jvde.us/xtb/XTBM_prototype.jpg
You may notice I also increased the X10 signal level resolution. (I deleted the "V's" from the display to cram on more data.)
During testing, one of my Maxi Controllers read out 130Khz. While I first suspected something was wrong in the code, checking with my digital scope confirmed the number was indeed correct. That is one of the ancient boxy Sears units, so it may have drifted from the nominal 120KHz over the years. A relatively new Leviton Maxi Conroller is exactly at 120KHz, and my TW751 reads 121KHz.
I was a bit surprised that X10 modules still work fine with a Maxi Controller that far off frequency. I was going to use frequency to recognize an Insteon transmission, but clearly that won't work by itself.
In addition to displaying VALID X10 commands, the unit will also display:
BAD START CODE (something other than 1110)
ERROR: COLLISION (too many bits received)
ERROR: BIT COUNT (not enough bits received)
ERROR: NOISE (for excessive noise on the powerline)
The modified prototype hardware is working well, and PCBs have been ordered. Availability should still be early fall.