Thanks for your reply.

I tried with BS217 mosfet, the result is same.

I checked with many IR transmitters and found that they use normal bi polar transistors to drive the IR LED, and the range they cover is over 20 feet some times. Even without any lens (Babar).

I am modulating the signal at 40Khz with 50% duty cycle.

I am planning to vary the frequecy with few KHz and very the duty cycle from 10% to 90% and will see the results.

Any suggestions ??????

Rauf