One question: why in these difficult propagation conditions whereIt's a matter of leveling the playing field Graham. The majority of
modems change speed when you increase their bandwidths so you can't do
an apples-to-apples comparison when one mode has a much faster character
rate than the others. The bandwidths of each mode may be the same, but
the character rates may be very different. That's a problem if you're
trying to test modes that fall into a specific character-per-second
range as I did.
Olivia and it's variants are the exception in that they can be
configured to achieve certain speeds regardless of bandwidth so you can
get close to another modes specs. That's done by either decreasing or
increasing the baud rate (number of tones) while leaving the bandwidth
From a practical point of view, I think a bandwidth of 250 to 500 Hz is
usually sufficient for keyboard chats. The path tests show that it's not
always necessary to increase bandwidth in order to improve throughput if
there's another more robust mode available.