Here's a few comments:
1) Read Barry Gordon's explanation of Pronto Hex, which is the format I suppose you are referring to.
2) You'll see that the format of Pronto Hex doesn't permit describing IR signals without modulation, because durations are specified in unit of the modulation period.  Other formats do allow one to describe a signal with no modulation, although many transmitters won't actually send such a signal, since the increased on time may burn out the LED.
3) You don't actually say what you're trying to do.