[time-nuts] EFC tracking

[Steve Rooke]

On 27 June 2010 10:05, Chris Stake <stake at btinternet.com> wrote:
> Here we go again

OK, firstly I must apologise to the list for generating a large amount
of, useful, traffic on this topic as it seems to have upset some.
Maybe it's because of the sensitivity to run away threads caused by
the TPLL debarcle or maybe it's just that no one wants to listen to me
any more. I don't know but I am now going to take this discussion off
line and correspond to those kind members who have shown an interest
directly. This will spare the rest of you the burden of listening to
this seemingly OT subject (although I assure you it is definitely on
topic).

I'll just clarify some points here, I am expecting to take
measurements at a rate in the order of 1ks/s so that the idea of
taking 64k samples to resolve one data point via FFT is going to be
out of the question. I will only be measuring over a matter of
minutes/hours not days as I'm looking for short term effects. As for
resolution, 16 bits would be ample for my needs and considering that
the average ocxo's EFC operates over, say, a range of about 5V but I
only need to look at part of that range, I can probably voltage shift
the +-1V range of an average sound card and get perhaps a bit or two
for free on that.

Please contact me via PM if you would like to assist me further. I
wish to thank all of you who have given your advice to me, I am most
grateful for your time.

Thanks,
Steve


> C
>
> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
> Behalf Of Poul-Henning Kamp
> Sent: 26 June 2010 21:06
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] EFC tracking
>
> In message <4C265BB1.8090902 at earthlink.net>, jimlux writes:
>
>>sound card ADCs, the high end 24 bit ones, are pretty darn linear [...]
>
> That is actually a very debatable proposition, a lot of them are
> tracking types that conveniently cover up any lack of linearity
> on the analog side of the fence.
>
> The major problem with using sound ADC's is that their references
> has absolutely no long term stability, so you will see your EFC
> wiggle and wander all over the place, even when it stays perfectly
> still.
>
> I would find one of those cheap-ish DVM's with a serial or USB port...
>
> --
> Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
> phk at FreeBSD.ORG         | TCP/IP since RFC 956
> FreeBSD committer       | BSD since 4.3-tahoe
> Never attribute to malice what can adequately be explained by incompetence.
>
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-- 
Steve Rooke - ZL3TUV & G8KVD
The only reason for time is so that everything doesn't happen at once.
- Einstein