Re: LF: Testing Audioinjector Octo with RPi3

[DK7FC <selberdenken@posteo.de>]

...oh, then it may help to switch a impedance converter between the 
pulse forming RC network, like a non-inverting OP with gain 1.
73, Stefan

Am 17.02.2018 22:09, schrieb Paul Nicholson:
> These glitches on the Octo input occur as the input signal
> passes through about +/- 1.4 volts.   Regardless of the
> digital gain control setting.
>
> Still present if I bypass the input board and wire straight
> into the differential inputs on the Octo card.
>
> Vanishes if I sample at 48k/sec instead of 96k/sec.  I get
> about 30nS jitter on the PPS at 48k/sec.
>
> To eliminate vlfrx-tools I reproduced the fault using arecord
> into sox to convert to ASCII data and then plot with gnuplot,
>
> Occurs on two specimens of Octo and two Pi.
>
> If I keep the input signal below 1.4 volts, there are no
> noticeable artifacts but the PPS jitter is still no better
> than about 200nS at 96k/sec.  The PPS is visibly noisy on
> the scope at 96k/sec but looks clean at 48k/sec.
>
> Tomorrow I'll look at the noise floor at various sample rates.
>
> --
> Paul Nicholson
> --