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 <[email protected]> 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. > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
