[time-nuts] Announcing the TAPR "FatPPS" Pulse Stretcher

[Robert McGwier]

If you are using the pulse to estimate the transfer function of a system 
and you do not want to have to factor out the squared off pulse, the 
shorter the better.  This is to be balanced against spreading the energy 
out so much that you have to nearly overload the measured system with 
the pulse or have so little energy in your region of interest that the 
noise floor rises to greet you and ruin you!  A pulse train helps but 
then there are other ambiguities to deal with as well as the need to 
decide on the pulse repetition frequency that does you the most good.

I have stolen and adapted various things to do this from Clark and his 
VLBI work.

Bob McGwier



John Ackermann N8UR wrote:
> Normand Martel wrote:
>   
>> I've made a such pulse stretcher to render the 1ms
>> pulse from a CMC Superstar and the 10µS pulse from a
>> Trimble Lassen SK8 visible via an L.E.D. by using a
>> simple 555 timer configured in a monostable fashion.
>>
>> Sure it is not nanosecond precise and i'm not sure AT
>> ALL it will react to a 20ns pulse, but for a visual
>> monitoring, it is perfect (pulse stretched to about
>> 30ms).
>>     
>
> Hi Normand --
>
> I don't know of anyone who actually *has* to deal with a 20ns pulse, but 
> it was interesting to see what the chip could do.  I actually tested 
> down to 8ns and it worked there, but I like to be a bit conservative 
> when quoting performance.
>
> The main raison d'etre for the FatPPS is to deal with the typically 20us 
> pulse width that comes from HP clocks.  That's just a bit too short to 
> reliably trigger a serial port.  I also wanted to be able to easily turn 
> a negative-going RS-232 pulse (which is what comes out of the Z3801A 
> after the "standard" RS-232 modification) into a positive going pulse to 
> feed the high-resolution Soekris net4501 time server.
>
> John
>
>
>   


-- 
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