[time-nuts] KD2BD WWVB receiver/decoder in QEX
alan.melia at btinternet.com
Mon Nov 23 04:46:49 EST 2015
Thanks Bill I had not looked at the date of the latest bulletin just that it
was still available. I suspect the major use now is the timecode.
----- Original Message -----
From: "Bill Byrom" <time at radio.sent.com>
To: <time-nuts at febo.com>
Sent: Monday, November 23, 2015 12:12 AM
Subject: Re: [time-nuts] KD2BD WWVB receiver/decoder in QEX
> The last NPL MSF Bulletin showing their errors was over 4 years ago:
> The error at a receiver over an interval of a couple of days is nearly
> completely due to propagation effects. The variations in propagation
> delay far exceed the error in transmitter frequency/phase control unless
> there are large changes in the local weather at the transmitter site.
> The phase of LF signals at 60 kHz is affected by the effective height of
> the ionosphere, which forms a 60 kHz waveguide with the Earth's surface.
> Unless you are very close to the transmitter, the amplitude and phase of
> the received signal change significantly through each 24 hour period.
> WWVB clocks should always measure the signal during the dark path (when
> the propagation path between Ft Collins CO and your location is fully
> dark), since that is when the signal is strongest and tends to have a
> more stable phase.
> WWVB clocks can get UTC with an uncertainty of about 100 microseconds,
> according to NIST: http://www.nist.gov/pml/div688/grp40/wwvb.cfm
> Bill Byrom N5BB
> On Sun, Nov 22, 2015, at 04:16 PM, Alan Melia wrote:
>> Hi Bob I have just realised that MSF may work diffently?? The Anthorn
>> signal is monitored by NPL at Teddington, West of London and frequency
>> off-sets twice a day are published in parts in 10^12 on their
>> web-site.....involving lot of averaging I think. They do not recommend
>> using the signal after dark.
>> You certainly could predict roughly the the skywave phase change during
>> day and the variation as the sun angle changes on the path over the year.
>> gets more difficult if there are flares or geomagnetic storms. If two
>> independent stations at slightly different distances collect information
>> could be corrected even more accurately.
>> The same ionospheric problem occurs of course with Loran, and the now
>> Decca system..
>> ----- Original Message -----
>> From: "Bob Camp" <kb8tq at n1k.org>
>> To: "Nick Sayer" <nsayer at kfu.com>; "Discussion of precise time and
>> measurement" <time-nuts at febo.com>
>> Sent: Sunday, November 22, 2015 7:34 PM
>> Subject: Re: [time-nuts] KD2BD WWVB receiver/decoder in QEX
>>> The most basic gotcha with WWVB is that propagation can (and does) shift
>>> carrier more than a full cycle over the course of a day. That’s at 60
>>> so one
>>> cycle is a lot (as in 16.666 ppm). Even at one second with a not so
>>> and a poor antenna, GPS should give you ~0.01 ppm. Right up front, you
>>> have a bit of a problem.
>>> (Yes I’m mixing measurements in that comparison, but the point is still
>>> What I keep wondering is - There is no big mystery about the WWVB
>>> location. You likely know your own location as well. Part of
>>> the data
>>> gives you day of the year. From that you can figure out some of the
>>> of the
>>> propagation effects (sunrise is at X:XX sunset is at … etc). You also
>>> could grab stuff
>>> like weather data fairly easily (no idea if that actually helps). If you
>>> fit out the basic
>>> propagation impacts, WWVB could get a lot better. At the very least, you
>>> would know
>>> when to ignore the signal.
>>> So yes, you could do better today than they could back in the good old
>>> days in terms of
>>> the propagation coarse effects.
>>> Unfortunately, there also is data on 24 hour comparisons of WWVB carrier
>>> (same time of
>>> day, one day apart). If you pick your time right (noon or midnight), the
>>> variable propagation
>>> can be reduced quite a bit. Based on that data, you are doing well at
>>> ppt over
>>> 24 hours. Might the new modulation help that by 10X? ..maybe. GPS over a
>>> 24 hour
>>> period should be giving you something in the 0.1 to 0.01 ppt range (same
>>> sort of pick a likely
>>> stable ionosphere time slot and compare).
>>> Does that make a WWVB device un-interesting? Not by any means. If you
>>> stretch out the
>>> time, both systems get down into the “I have nothing else that good”
>>> range. Checking one
>>> against the other is indeed an interesting thing to do. You just need a
>>> **lot** of time to do it.
>>>> On Nov 22, 2015, at 12:41 PM, Nick Sayer via time-nuts
>>>> <time-nuts at febo.com> wrote:
>>>>> On Nov 22, 2015, at 7:47 AM, paul swed <paulswedb at gmail.com> wrote:
>>>>> As mentioned a nice answer to the wwvb modulation change.
>>>>> I looked up the parts and it seems that they have gone into the NOS
>>>>> Though you can get some from digikey and such especially in the SOIC
>>>>> package. Also the VCO isn't available.
>>>>> It appears that the Chinese sight has the lmc6484 and LM387n at
>>>>> prices for small quantities. Most likely will order from there.
>>>>> Have not checked out the PIC chip yet.
>>>>> The 74HCXX are common and reasonable.
>>>> That’s kind of a shame. I’m sure a redesign with modern SMD parts could
>>>> be accomplished.
>>>> The big question is how the stability of a wwvb disciplined oscillator
>>>> would compare to a GPS disciplined one (all other things being equal).
>>>> Well, it’s a big question for me, since I have no idea, but I imagine
>>>> simply asking here will give an immediate answer. :)
>>>> I’d have to guess that the PLL would behave better given a 60 kHz
>>>> reference rather than a 1 Hz one. But how stable is that 60 kHz
>>>> after going through, what, a thousand miles of ionosphere or so?
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