[time-nuts] Why are PPS pulses so narrow? (was: 53132A triggering)
kb8tq at n1k.org
Fri Sep 16 21:03:12 EDT 2016
It is sort of an " everybody does it " sort of thing. Various justifications:
Less power is used / less heat in the drivers and terminations.
Transformer coupling works better ( lower delay ) with narrow pulses
Anything over 1 us has been "really long" in terms of logic speeds since the 1960's
A definite duty cycle "bias" let's you detect an inverted pulse.
The only real reason is "that's the way it's done". Big Customers ask for it that way. Suppliers deliver what is asked for. Nobody complains, nothing changes.
> On Sep 16, 2016, at 7:44 PM, Peter Vince <petervince1952 at gmail.com> wrote:
> Can I ask why PPS pulses are so narrow? It makes them difficult to see on
> a 'scope, and difficult to detect on a PC. And, as Bob said, far less
> obvious if you trigger off the wrong edge.
>> On 16 September 2016 at 23:55, Bob kb8tq <kb8tq at n1k.org> wrote:
>> Most PPS signals these days are very low duty cycle. If you AC couple
> them, you can easily be triggering on the wrong edge. With the narrow pulse
> it may not be very obvious.
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