N4148 diode's purpose

[tomas]

Hi, can anyone tell me, what is the purpose of 1N4148 diode on page 7? **broken link removed**

Thanks for answer

 

[jiripolivka]

The two transistors, T1 and T2, form an oscillator with the T2 acting as pulse detector. The 1N4148 diode creates the base DC bias of ~ 0.7 V for both T1 and T2 and adjusts T2 to detect pulse amplitude.
You can try to put a 1kOhm resistor in its place and see if the detector becomes less sensitive.