There is no limit to AM modulation, it is not limited to 100 percent
in the positive direction. It is limited to 100 percent in the negative
direction, to prevent cutoff. Positive limits are set by the mdoulation
linearity of the output stage with increasing positive voltage.
Most AM BC broadcasters in this country use assemtrical modulation
for this reason.

You're dead right of course Peter.

i believe you're AM broadcasters are limited to 125% positive while here
in the UK we have 100% positive peak limit.

FYI the late model Nautel PDM broadcast transmitters are capable of
around 200% positive peak and up to 50KHz in frequency response!

Broadcast transmitters are limited for obvious reasons.
--
Philip de Cadenet G4ZOW
Transmitters 'R' Us
http://www.transmittersrus.com