Most likely what you have is the 'standard' IR (as in TV remote) signal
which is either 40khz (or sometimes 38khz) on-off modulation, which
is then further 100% (as in AND) modulated by the 'iintelligence', i.e.
the raw RS-232 1/0 stream. If you have a scope (sounds likely) and
just repeatedly send some CHAR you should recognise it. The hobby
robotics types do this all the time , usually with a 555 timer free
running
40 khz 50% duty cycle modulated by the (TTL level) RS232 signal.

You need to observe polarity so that one one the 1->0 inversions
that happen in serial transmissions don't trip you.

Others 'bitbang' the serial stuff and provide the 40khz at the micro.
I.e the bit time is some fixed # of 40khz cycles.

Many devices use a 'standard' receiver part which has about a 2khz
'band pass' (i.e some on-chip lumped component filter)so the oscillator
doesn't need to be dead on. Some assembly required, tell us how you
made it play.

There are various articles, etc. E-mail me if you need them.

R.Martin