John thats right and the extra bit is the data channel. Though your homebrew receive may detect and lock. There is only 1 site so you can't actually navigate. They fake the receivers out by having the same transmitter act like two. Regards Paul WB8TSL
On Fri, Feb 3, 2017 at 12:58 PM, John Ponsonby <[email protected]> wrote: > I have a three channel LORAN-C receiver of my own design which I made over > thirty years ago. I built it for navigating my small yacht. I think the > eLoran signals are compatible though of course my receiver doesn't have the > means to extract the data channel. > Here follows a brief tutorial. > All LORAN-C stations transmit on 100kHz precisely. The signals come in > groups of eight pulses spaced precisely 1ms apart. Master stations transmit > a ninth identifying pulse spaced 2ms after the last of the 8 so they look > like: {●●●●●●●● ●} The phase of the RF is switched between 0° and 180° > according to a fixed pseudo-random pattern from pulse to pulse. There are > two phase patterns, the A pattern and the B pattern, and these alternate > from one 8 pulse group to the next. The Master patterns are different from > the Secondary patterns. Each LORAN-C chain has its own GRI (Group > Repetition Interval) and this is the number of ten's of μs from the start > of one 8 pulse group to the start of the next. > For precise navigation one needs to lock onto the ground-waves. If the > receiver is far from a transmitter the skywave can arrive very shortly > after the ground-wave, so it is essential to only use the start of each > pulse. Officially one is supposed to lock onto the third positive going > zero crossing point on the rising edge of each pulse. Close to a > transmitter the skywave can arrive up to 1ms after the ground wave so that > it interferes with the start of the next pulse. The phase coding is > designed to avoid this causing trouble. The skywave delay varies with time > of day as the ionosphere goes up and down. > Because the wavelength is so long (3km), the near-field of the transmitter > extends quite a long way. That has the effect of changing the phase of the > received signal from what one might first think it would be assuming a > fixed velocity of propagation. The velocity of propagation is less than > the free-space velocity of light and is different between over-sea and > over-land paths. > My receiver just gives two relative time delays in μs and I used a TI59 > calculator to convert to latitude and longitude. The program only just fits > within the capacity of the calculator. > I don't know anything very specifically about eLoran but I think the main > modification is to add extra phase coding on the pulses to form the data > channel. > John Ponsonby > _______________________________________________ > 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.
