[time-nuts] [Fwd: Re: Simulating LORAN-A GRI Timing Generator]

J. Forster jfor at quik.com
Sat Jan 8 16:04:56 UTC 2011

> John,
> On 08/01/11 16:08, J. Forster wrote:
>> Pondering some more on this, doing some calculations (spread-sheets) the
>> actual scheme emerge... the range of 0 to 7 is not selected by accident.
> I had essentially the same spread sheet...
> However, how would you be able to achieve simplicity of design by being
> true to the PRI/PRR given or to what seems like reasonable counter based
> solution.

I think the PRR of the transmitters was crystal controlled. I'm gettring a
Test Set with a 1.81818 KHz crystal in it...  yes 1818.18 Hz!!...  that
simulates a transmitter.

The receive set seems to be free-running, crystal referenced. I don't
think it automatically locks up on the Master pulse. I see no indication
that the received signal connects to any timing stuff.

> Notice that the ARN-4 has a "Crystal phasing" control to
> adjust the crystal frequency of the receiver so that the receiver will
> align up to the actual rate of the master station.

The DAS-1 has a left-off-right control on the master crystal. It seems
like thye operator manually saligns the Master pulse, and the drift rate
is low enough to allow TD measurement.

> I think the PRI/PRR given is a presentation simplification rather than
> true numbers.

Certainly possible, althyough 100 uS increments is pretty simple too.

> Considering that absolute frequency was not a requirement,
> the repetition rate of the master needs to be sufficiently stable for
> distinction of station and the receiver to make stable reading, in
> presence of other stations.
> That LORAN-C uses GRI indications with repetition rate in microseconds,
> and fairly even such numbers as well, is another hint.
> Thus, I view the PRI/PRR ratios as approximations at best, a matter of
> presentation rather than actual nominal rates.
> Cheers,
> Magnus

I don't know. It's certainly an interesting possibility.




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