Message-ID: <002401c405d5$13549620$6507a8c0@Main>
From: "Alan Melia" <Alan.Melia@btinternet.com>
To: rsgb_lf_group@blacksheep.org
References: <7D653C9C42F5D411A27C00508BF8803D01A9F48C@mail.dstl.gov.uk>
Date: Tue, 9 Mar 2004 12:50:11 -0000
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Subject: LF: Re: RE: Ionospheric doppler ?
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Hi Alberto, Was this at daytime or during darkness I wonder?? My web site
carries a simple equation for path differences for a simple geometric
construction. I get  level changes in daytime here which could be
interaction between the groundwave and a one-hop skywave. I get quite
violent changes at night when there are often deep cancellations. I think
from memory the slant range path difference to give a concellation is about
3500m at 138kHz (at abt 700kms) so at 77kHz it would be about twice this.
This would equate to about 6.5usecs so a 200nsec difference is only a 5
degree phase swing......possible.....an interesting experiment. I wonder if
it would be better when you have a GPS 1pps. I have been musing the problem
of doing oblique "sounding" using sources like DCF, but have not cracked an
easy way to do it yet. As your path involves a trip over the Alps it might
even be that there is not much groundwave, and it is a multihop effect??

Cheers de Alan G3NYK
alan.melia@btinternet.com

----- Original Message -----
From: "Talbot Andrew" <ACTALBOT@mail.dstl.gov.uk>
To: <rsgb_lf_group@blacksheep.org>
Sent: 09 March 2004 12:19
Subject: LF: RE: Ionospheric doppler ?


> Usually these radio controlled clocks only check the time every few hours
or
> when they are turned on.  Normally the 1 pulse per second is just derived
> from the internal oscillator and I would expectyou to see the few
> parts-per-million drift of that, with a sudden correction from 'time to
> time'
>
> The fact that you were seeing a slowly changing varions plus / minus is
> surprising.
>
> I can observe doppler shift on MSF and DCF, but this is very pronounced at
> dawn and dusk  - a few parts in 10^-9 over tens of minutes, which is less
> than the 80 - 120ns on 1 second you saw
>
> Andy  G4JNT
>
>
> -----Original Message-----
> From: Alberto di Bene [mailto:dibene@usa.net]
> Sent: 2004 March 09 11:58
> To: LF Mailing List
> 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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