I'll make one more post on this issue.

You will notice that most of the popular bit-per-second rates are 2400*2^N,
where N ranges from 0 (2400 bits per second) to 4 (38,400) bits per second.

However 57,600 and 115,200 multiply in a factor of 3 (ie: 57,600 = 19,200 *
3, and 115,200 = 38,400 * 3).

So, a good crystal that would work with zero error for all these rates would
be any multiple of:

16 * 2400 * 2^4 * 3

or:  1,843,200 Hz

The largest such value < 4MHz is 3,686,400 Hz
The largest such value < 20MHz is 18,432,000 Hz

You will find crystals in both of these frequencies readily available.

Bob Ammerman
RAm Systems 

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