38khz, not Mhz .... it is the standard carrier frequency for IR remotes with typically low ambient interference. Most importantly you can get really convenient standard and fairly cheap receiver ICs like the TSOP1738 and similar that take a whole lot of pain away in decoding a 38khz modulated signal into simple carrier signal on and signal off pattern to do this manually , you would need photodiode+preamp+some kind of noise filter +comparator