[time-nuts] Simulating LORAN-A GRI Timing Generator

J. Forster jfor at quik.com
Sat Jan 8 15:00:43 UTC 2011

> John,
> On 08/01/11 05:04, J. Forster wrote:
>> Magnus,
>> See my post of a few minutes ago.
>> The GRI and Delay counters need to be 5 decimal digits. My current
>> thinking is manual entry of the numbers via BCD coded thumbwheel
>> switches.
> If you only need a static location that will be fine. Naturally you tune
> it up to the ships current (final?) position. Good exercise for the
> visitors. :)

True, and that's the plan. The TDs would vary very slowly when the ship is
underway anyway. Not something a visitor would really notice. Roughly, the
TDs change a microsecond for every 1/5 mile.

Clearly, if the TDs were settable from an external 'puter, a manovercould
be simulated, but visitors don't get to twiddle knobs (they steal them),
so a static display is probably best.

>> LORAN-A has 24 possible GRIs; in three blocks of 33 PPS; 25 PPS; and 20
>> PPS. It also has 4 RF frequencies.
> I did a fashinating read-up here:
> http://www.jproc.ca/hyperbolic/loran_a.html

Yes, Jerry's site is very good on many things like LORAN and radios and

> GRI is a LORAN-C term if I get it correctly, where as PRR is used
> together with frequency indication in LORAN-A.

You got me! Yes. GRI = 1/PRF. I prefer to deal with microseconds than 1/9

>> Currently I plan only one Slave, but a second would be an easy addition.
> Indeed. Considering the chain that used to be there, you could allow for
> two chains to be setup on the same frequency (1H chains).
> Cheers,
> Magnus

Right. Thanks,



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