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From: =?iso-8859-1?Q?Jos=E9_Manuel?= <jpradoes@telefonica.net>
To: rsgb_lf_group@blacksheep.org
Date: Wed, 10 Mar 2004 18:59:44 +0100
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Subject: LF: Fw: RE: Re: Ionospheric doppler ?
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Hello Alberto, Andy and the Group:

 Tom Van Baak has an interesting site (http://www.leapsecond.com/) about
 precision timing,  and a nice paper also about it
 (http://www.leapsecond.com/ptti2003/index.htm). He says about his atomic
 clock collection :"A man with one clock knows what time it is. A man with
 two clocks is never sure. But I would add further: A man with three clocks
 is more sure than a man with two clocks. And so the clock collection
 started... "

 73 de José, EA1PX


> ----- Original Message -----
> From: "Talbot Andrew" <ACTALBOT@mail.dstl.gov.uk>
> To: <rsgb_lf_group@blacksheep.org>
> Sent: Wednesday, March 10, 2004 12:03 PM
> Subject: LF: RE: Re: Ionospheric doppler ?
>
>
> After some detailed measuremetns on eight GPS receivers from different
> manufacturers, I've found that the modern ones mostly exhibit around 100ns
> jitter from second to second.  Older units like the Garmin GPS25 and
> Motorola Oncore (old favourites among the amateur community) give a few
> hundred ns.  But by averaging over longer periods, the jitter from these
is
> just as good as the later ones when averaged over the same period.
>
> This pulse to pulse jitter can often be reduced to a few tens of ns on
some
> modules by operating in position fix mode, but you need to have a module
> specifically optimised for timing purposes in order to do this;  these
> usually cost somewhat more than the standard navigation version.
>
> So far my favourite is the Jupiter T with its 10kHz output, making locking
> of an oscillator straightforward, as described earlier on this reflector.
I
> tried a Jupiter module directly locking a 10GHZ local oscillator,  but the
> raw signal is not good enough when effectively multiplied by one million -
> teh tone of a CW signal sounded much too rough. For high microwaves a long
> PLL time constant with a high spec OCXO is required.  But for use up to
UHF,
> the simple GPS disciplined oscillator described earlier is satisfactory.
>
> Andy  G4JNT
>
>
>
>
> -----Original Message-----
> From: José Manuel [mailto:jpradoes@telefonica.net]
> Sent: 2004 March 10 10:11
> To: rsgb_lf_group@blacksheep.org
> Subject: LF: Re: Ionospheric doppler ?
>
>
> Hi Alberto ad all:
>
> When you install the GPS I think that you´ll probably find short-term
> variations in the same order, + - 100 nsec.
>
> 73 de José, EA1PX
>
>
>
>
> ----- Original Message -----
> From: "Alberto di Bene" <dibene@usa.net>
> To: "LF Mailing List" <rsgb_lf_group@blacksheep.org>
> Sent: Tuesday, March 09, 2004 12:57 PM
> Subject: LF: Ionospheric doppler ?
>
>
> > Hello Group,
> >
> >   I made yesterday an interesting experiment and would like to know your
> > opinions about it.
> > Waiting for the weather to become such to allow me to go on my roof
> > to install there a GPS antenna, in the meantime I started to play with
an
> > inexpensive radio-controlled clock, made by Conrad, bought a few years
> > ago at the Friedrichshafen Messe in Germany, which receives the DCF-77
> > signal.
> > This clock has an output meant to drive an external electro-mechanical
> > hand clock, and on this output there is, of course, an 1pps pulse.
> >
> > I have an HP-5328B Counter, with a 10811 OCXO which is always (24/7) on.
> > My shack is in the basement, with a constant temperature of 21 Celsius,
> > no drafts,
> > so any variations in the measured frequency or time is real, and not an
> > artifact
> > of the counter.
> > The 5328 has a sort of reciprocal counting feature, where you can use an
> > external signal as a gate for an internal 100 MHz oscillator, phase
> > locked to
> > the OCXO. In addition you can prescale the external signal.
> >
> > So what I did was to prescale by ten the 1pps signal from the clock,
> > then used
> > this 10 second interval to count the internal 100 MHz oscillator, giving
> > a resolution
> > of 1 ns.  If everything were perfect, I should have obtained a count of
> > exactly 10^9.
> >
> > What I measured was a value that differed from the ideal by an amount
> slowly
> > changing with time, ranging from -80 ns to + 120 ns. The count was very
> > consistent from period to period, showing no short term random jitter.
> > In one case I measured a variation of about 100 ns in a time lapse of
> > roughly
> > one hour.
> >
> > I am by no means an expert in propagations and ionospheric effects, so
> > my question
> > is : are the values I measured compatible with what is known about
> > ionospheric doppler ?
> > If not, what else could be an explanation of that slow change ? I would
> > tend to exclude,
> > for the reasons reported above, an artifact of the HP counter.
> >
> > Thanks for any explanations
> >
> > 73  Alberto  I2PHD
> >
> >
> >
> >
> >
>
>
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