generating 10-100 ns pulses with 20 Hz frequency
When you're a programmer, every problem can be solved with a microcontroller...

Perhaps overkill, but an ATtiny4/5/9/10 (SOT23-6) running at 12 MHz can be programmed to pulse any of its three (four) I/O pins for as low as 83.3 ns at any time interval from 166 ns to over 5 seconds.