[time-nuts] Why are 1PPS signals so skinny?

[Rick Karlquist]

Mark Sims wrote:
>
> My first inclination,  if I were building a timing receiver,  would be to
> make the PPS output a nice,  symmetrical square wave.   But pretty much
> all GPS timing receivers output an anorexic,  dinky little heroin addicted
> supermodel sized pulse (from 1 to 150uS wide is typical).
> _______________________________________________

One reason might be that it is convenient to have AC coupled
hardware, with a reasonable low frequency cutoff.  1 Hz is
not a reasonable low frequency cutoff, which is what you
would need if a square wave were used.  (Actually, to accurately
reproduce a 1 Hz square wave requires response down to .1 Hz
and preferrably .01 Hz, due to droop and phase shift distortion
issues).   A short pulse will conveniently propagate though
the same sort of distribution amplifiers used for 10 MHz, 5 MHz,
100 kHz, etc.

Rick Karlquist N6RK