[time-nuts] eLoran test

paul swed paulswedb at gmail.com
Fri Feb 3 16:25:34 EST 2017

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.

On Fri, Feb 3, 2017 at 12:58 PM, John Ponsonby <jebponsonby at gmail.com>

> 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
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