IR reciever's transmission distance
This chip  uses AGC with a BPF with a Q of ~10 to improve the Signal/Noise Ratio and thus has a wide dynamic range for distance and rejection of noise.  A simple output comparator detects the pulsed Off duration of light relative to the peak which is regulated by AGC.  i.e. steady carrier =0. Pulsed off =1

The necessary conditions for a "0" active output are the IR wavelength ought to be 950nm  +/-100nm (50% loss), modulated at 38kHz ( 5% error reduces signal 50%) and sustained initially for 0.8ms then may be further modulated on/off with 600us bits or 1.67kbaud roughly, although 1200baud is ideal for range or >10 carrier cycles per bit.


  The wide range of reception for distance is owing to the wide automatic gain control range (AGC) of burst pulses in a narrow bandwidth (Q=10) of pulses,  wavelength of light and built-in electromagnetic shielding of the Photo Detector (PD) and amplifier. A clean power supply is essential.


The lens gives some gain in the horizontal axis on center but still a total reception angle of ~130 deg at half power.

Path loss (like Friis loss for RF) follows an inverse squared dynamic loss measured with signal power sensitivity of 0.35 (typ)  mW/m². 

The threshold for detection is fixed such that ambient noise is unlikely to trigger the duration of a start pattern needed to decode a command if there was any noisy output.  This requires a sustained modulation of 38kHz pulsed IR for at least 0.8ms to allow AGC to capture the signal before the data bit follow by varying the duty cycle. 

It has high rejection of 100/120Hz flicker in addition to the black tinted "Daylight Blocking filter" which is transparent at IR wavelengths.