Marc Ramsey wrote:
Uh, no Mr. Boffin, tis not quite that simple. It's been a while since I
looked at this stuff, but I believe the actual transponder code is
encoded using a modified Gray code (as is the altitude code), so the
actual duty cycle is not quite that obvious. Second, the fashion in
which the transponder code and the altitude code are transmitted differ
significantly, as the transponder code portion of the transmission dates
back to WW II IFF, and the Mode C stuff came much later. I doubt the
NTSB would have brought it up, unless there was something to it.
Personally, I'm not interested enough to try to figure it out...

I'll take it back, Mode A and Mode C are transmitted the same way, and
while altitude is Gray encoded, the squawk code is straight binary. So,
I have no idea what the NTSB was talking about.

Marc