[time-nuts] Basic question regarding comparing two frequencies

[paul swed]

Oh indeed I agree John.
LORAN has spoiled me also at least till nov I hear.
The Canadians are a drop better then us at saving the system.
I am definitely figuring out the old ways and can't say that I like it all
that much.
Always have gps for the moment.

On Fri, Jul 30, 2010 at 10:08 AM, J. Forster <jfor at quik.com> wrote:

> Partly.
>
> There are hourly jogs in the WWVB signal and also diurnal shifts of the
> order of a cycle at 60 KHz.
>
> The Fluke receivers havs a counter for microseconds, but it's difficult to
> intrerpret w/o the stripchart too.
>
> Frankly, 60 KHz is a PITA IMO. Oh for LORAN!
>
> -John
>
> ==========
>
>
>
>
> > So on a 60 khz signal the long strip chart recorder is simply a super
> long
> > low pass filter averaging out the doppler somewhat. It really doesn't do
> > that well. The mark-1 eyeball does a better job. Right?
> >
> > On Tue, Jul 27, 2010 at 4:53 AM, Geoff <vk2tfg at ozemail.com.au> wrote:
> >
> >> On Tue, 27 Jul 2010 09:08:49 am Chuck Harris wrote:
> >> > I suppose that you could always cheat?  Since you know where the
> >> > transmitter is going to be, if you could get a timenut near to the
> >> > transmitter to give you a beacon to measure 24hrs prior to the event,
> >> > you could use the diurnal variations that you observed (observe?) on
> >> > the beacon to predict the skywave offset due to Doppler at the time
> >> > of the event.
> >> >
> >> > -Chuck Harris
> >> >
> >> > Murray Greenman wrote:
> >> > > You guys are trying to crack a nut with a sledgehammer!
> >> > >
> >> > > For a start, as Didier says, you can't possibly read the frequency
> >> of a
> >> > > sky-wave signal to 0.01Hz in any short time frame since the Doppler
> >> on
> >> > > the signal can be as much as 1ppm (i.e. 10Hz at 10MHz). You can only
> >> > > infer it closer than that by studying the frequency in the very long
> >> > > term.
> >> > >
> >> > > In addition, you'll never know how much of the daily variation is
> >> > > ionospheric, and how much is due to thermal changes at the source.
> >> snipped
> >>
> >> There is one possible way of getting an accurate reading from a sky wave
> >> signal over a short(ish) period. Plot a doppler shift curve with as fine
> >> a
> >> resolution as you can manage. Then look for a point of inflexion in the
> >> curve, that is a point where the second derivative of the curve function
> >> is
> >> zero. The frequency at that time will be that transmitted as at that
> >> instant
> >> the path length is not changing. You may have to examine your data set
> >> visually and mathematically examine a much smaller section. Of course if
> >> you
> >> don't get a point of inflexion you'll need much more data :-).
> >>
> >> Cheers, Geoff vk2tfg.
> >>
> >>
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