John,
I think the problem is that your software is making the assumption
that the other end is receiving using USOS. So it does not send a
<LTRS> shift between 599 and FL, but instead depends on the receiver
to obey USOS and to automatically shift to <LTRS> after the space
between 599 and FL.
Remember that a SPACE can be sent in either FIGS of LTRS shift, so
there is no explicit LTRS shift that is sent between the 599 and FL.
I.e., I wouldn't be surprise that your output Baudot stream looks like
<5><9><9><SPACE><F><L>. Which is received as "599 !)" by someone who
does not use USOS.
In my implementations of USOS, I have tried to make sure that what I
send can be read by both a USOS receiver and a non-USOS receiver.
I always prefer sending something like <5><9><9><SPACE><LTRS><F><L>.
The exchange is intact whether the receiver has USOS turned on or
not. And "599 599" is sent as <5><9><9><SPACE><FIGS><5><9><9>.
If the software that you use is not open sourced and and there is no
way for you to selectively apply USOS to receive but not to transmit,
you can resort to sending "599-FL FL". This will force your software
to send a <LTRS> after the dash. The second SPACE will still provide
robustness to a USOS receiver, and you have used up only an extra 1/7
of a second.
Do not send 599-FL-FL because you will be sending oodles more
<FIGS>and <LTRS> and still end up not benefiting when the receiver is
on USOS.
73
Chen, W7AY
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