[time-nuts] Some long-term data

Magnus Danielson cfmd at bredband.net
Sat Dec 23 19:21:47 EST 2006

From: John Ackermann N8UR <jra at febo.com>
Subject: Re: [time-nuts] Some long-term data
Date: Sat, 23 Dec 2006 17:53:50 -0500
Message-ID: <458DB37E.1040504 at febo.com>

Hi John!

> Magnus Danielson said the following on 12/23/2006 05:22 PM:
> > Such as temperature and humidity. One of the Cesiums seemed to have a rather
> > large frequency offset. Did you drift-compensate your ADEV measures or not?
> No, I ran the ADEV in Stable32 without removing drift.  My understanding
> is that linear drift shouldn't affect the calculation.  I was also a
> little concerned whether drift removal would work very well given that
> both Cesiums had periods where the offset changed for quite a long
> period (CS1 near the end of the data, CS2 at the beginning) and I wasn't
> sure what impact that might have.

I know next to nothing about Stable32, so I don't know what that black box
actually is doing.

>From a theory standpoint, it is trivial to show (I've done the exercise to
convince myself, but it is already covered in literature) that linear frequency
drift does affect the result. Time/phase offset and frequency offset cancels.

>From a practical standpoint, linear frequency drift may or may not be small
enought not to interfere with the measure of the noise power. To be sure,
measure the drift rate.

> > (Actually, if you hand me the raw data I would love to do some exercises on
> > them.)
> I'll be happy to ship the data to anyone who's interested.  Each file is
> about 600kb before compression, and it compresses well.

No problem!


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