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From: Terry G0EZY <GW0EZY@sky.com>
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Date: Sat, 17 Jun 2017 12:42:52 +0100
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Subject: Re: LF: Octo-soundcard for the Raspi
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 >>Does it look anything like http://abelian.org/vlf/tmp/170617a.gif

Yes that's it!

I have a 100k from the +5 PPS output in series with a 2.2 uF to ground. 
The PPS output to the Octo is taken from the RC junction.

 >>Is it possible to reduce the PPS pulse width?  Say to 10mS or 5mS?

The Garmin can be programmed for pulse length but also being used for SL 
timing. Might be easier to user a stand-alone GPS like the Ublox NEO-6M 
GY-NEO6MV2 used by Stefan.

Terry


On 17/06/2017 11:25, Paul Nicholson wrote:
>
> Terry wrote:
>
> > I have to sort out now is the timing pulse. it looks
> > horrible on vtscope, a sort of double humped thing
>
> I'd guess you have some high pass applied to the shaped
> PPS, perhaps the input stage of the Octo?
>
> Does it look anything like http://abelian.org/vlf/tmp/170617a.gif
>
> Is it possible to reduce the PPS pulse width?  Say to
> 10mS or 5mS?
>
> > Are you using a square pulse from the GPS to feed
> > the RC conditioner?
>
> Yes, it's a 2mS rectangular pulse from the GPS, through
> a buffer (a hex inverter), then a simple RC low pass
> filter to shape the pulse suitably for centroid measurement.
>
> -- 
> Paul Nicholson
> -- 
>
>