[time-nuts] WWV Doppler Shift

Bob kb8tq kb8tq at n1k.org
Tue Nov 20 23:43:08 UTC 2018


Hi

Having looked at WWV with a Carrier -> BFO -> audio card approach (and a radio 
locked to an Rb standard …) you have dig a bit to find a situation that is
beyond a tenth of a ppm. If you average over minutes  or tens of minutes (which 
is exactly what you do with WWVB) the only time you get past 0.1 ppm is the 
same sort of day/night propagation mode shift that drives WWVB nuts ….

Bob

> On Nov 20, 2018, at 5:35 PM, Donald E. Pauly <trojancowboy at gmail.com> wrote:
> 
> That was the first time that I had seen an xy plot of WWV versus a
> stable crystal oscillator.  It is even worse than I thought.  I had to
> look up FRK to see that it is a rubidium standard.  I talked to Jim
> Maxton the chief engineer of WWVB many times around 1995.  At the time
> I was in Gila Bend 80 miles southwest of Phoenix.  He had a Hewlett
> Packard cesium standard at Ft Collins.  They were using a dual view
> GEOS Geostationary satellite to set the cesium to match the master
> clock in Boulder.  If the cesium was good to 10^-13, that is 8.6 μs
> per day.  I can't remember how close he tried to keep it or how often
> he adjusted it.  It looked like that I could determine the start of
> the second to the individual transmitter cycle.  Time transfer
> accuracy was therefore limited to the height changes of the ionosphere
> at sunrise and sunset.
> 
> The main disturbance was wind blowing the antenna.  Ordinarily the
> phase would jitter a few degrees per second.  I could tell the wind
> speed by the phase jitter without checking the Ft Collins weather.  If
> memory serves, the loaded Q at 60 kc was about 200.  A half percent
> tuning error caused a 45° phase error.  I have seen a 45° excursions
> on several occasions over a minute more than once.  My receiver had a
> slow lock mode that could spot them.  It also had a 45° phase switch
> on the 100 kc local oscillator to eliminate the station ID from 10 to
> 15 minutes after the hour.  There was therefore no disturbance in lock
> during it.  I was never able to measure any error in the 45° phase
> advance.  One degree would have been obvious.
> 
> When I first got my receiver going, the phase would advance nearly 40°
> at the start of the second when the power was reduced by 10 db.  It
> had been doing so for years and nobody noticed it.  Maxton took an
> unneeded condenser out of his time code generator which fixed most of
> it.  The new transmitter fixed the rest.
> 
> Ft Collins is at 5,003 ft and clocks there run fast by 1.663·10^-13.
> (g/c^2)/meter) compared to sea level.  How did you correct for
> altitude on yours?  I presume that frequency is defined at sea level
> but I don't know that.  Sea level clocks at the North or South Poles
> run fast relative to those at equator sea level by 1.192·10^-12.
> 
> WB0KVV
> πθ°μΩω±√·÷Γλφ|Δ
> 
> On Tue, Nov 20, 2018 at 9:06 AM jimlux <jimlux at earthlink.net> wrote:
>> 
>> On 11/20/18 1:54 AM, ew via time-nuts wrote:
>>> Starting 1970 I used a modified Tracor 599H on WWVB  with excellent results. It had a mechanical counter with 100 nsec, resolution. Noisy but perfect. Yes you have to take Ionosphere sunrise and sunset in to consideration and the hourly shift, but being a very early riser  4AM because of Europe no problem. Better than 2 E-11 per day and 4 E-14 per month.
>>> 
>>> In the 90 ties with my FRK having temperature and aging control frequency was better than 1 E-12 all the time.
>>> 
>>> Bert Kehren
>>> In a message dated 11/19/2018 9:58:39 PM Eastern Standard Time, trojancowboy at gmail.com writes:
>>> 
>>> HF propagation of WWV or WWVH is horrible compared to VLF propagationof WWVB at 60 kc.  In this video the 5 mc WWV signal from Ft Collins,Colorado is being received in New Jersey.  It was compared against astable 5mc crystal source.  You can see a shift of a few cycles persecond over a few seconds.  This is due to the movement up or down ofthe ionosphere at a substantial fraction of the speed of sound.
>> 
>> In general terms, the coherence time of the ionosphere is single digit
>> seconds - that is, there's essentially no correlation between
>> propagation path at one time and the propagation path 10 seconds later.
>> 
>> The "general length" of the path will be the same, but the details
>> different.
>> 
>> The actual ionization in the ionosphere can best be described as moving
>> "clouds" there's a fair amount of spatial inhomogeneity.   In the same
>> sense that milk reflects light from a multitude of little fat globules.
> 
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