On 2012-01-11, David J Taylor <[email protected]> wrote: > "unruh" <[email protected]> wrote in message > news:[email protected]... > [] >> Just like the rs232 specs say at least -3V to +3 V for the signals, when >> most rs232 cards will accept +.5V to +2 V for the transition levels. >> What the specs say and what the card does need not be the same. People >> have claimed that the Garmin 18x actually does significantly better than >> 1us but I have not tested it. > > 1 us accuracy, not pulse width. GPS 18x LVC. See para 4.4.1 > > http://www8.garmin.com/manuals/GPS18x_TechnicalSpecifications.pdf > >> If I had you believing that the Oncore had a width of 1us, I appologise. >> That is certainly wrong. I have not measured it, so cannot say what its >> width actually is. I have looked at the Sure, and its pulse width is >> about 5ns. > > No, the Sure unit outputs a 100 ms wide pulse. I have not measured its
Sorry, it risetime width. > risetime. The stated accuracy for "time" is 20 ns, but the Web page does > not state where that 20 ns is measured - it may be internal to the chip. > I would expect it to be neither significantly better nor significantly > worse than the Garmin. 20ns is significantly better than 1000ns (a factor of 50) . The risetime, as stated, I measured to be about 5ns. And much of that error is due to the sawtooth error in the output. (As I understand it, in order to make things simple, the pulse is emitted at a the nearest zero crossing of the internal oscillator, rather than exactly on the time. Thus the actual time of the pulse wanders depending on the phase of the interal oscillator with respect to the actual time. The oncore reports that difference so you can, post facto, correct for that error in the output pulse time compared to the true second crossing. The sure, AFAIK does not, so it has an inherent error due to this. (sawtooth because the phase of the internal oscillator drifts with respect to the true time and thus slowly increases until it reaches 180 degrees and then jumps back down to 0) > > http://www.sureelectronics.net/goods.php?id=99 > http://www.sure-electronics.net/download/GP-GS010_Ver2.0_EN.pdf > > David > _______________________________________________ questions mailing list [email protected] http://lists.ntp.org/listinfo/questions
