[time-nuts] Old Loran
namichie at gmail.com
Sun Jul 13 19:19:12 EDT 2008
The technology of that era is quite interesting.
1961 I was working on an Australian air navigation system called DME,
which measured the distance to a selected airport transponder.
Oscilloscopes were very crude by today's standards. A 1MHz LC
oscillator was adjusted to zero beat a 1MHz xtal osc.
The 1MHz oscillator was then pulsed to start with the synch pulse of
the CRO to superimpose little microsecond
pips on top of the signal being viewed. (only single beam CROs then,
using a 5BP1 tube). That way we had a scope calibrated in microseconds.
Stable delays were either a row of maybe 40 capacitors and coils to
make a lumped constant delay line,
or a box with 100s of yards of coax and a pair of connectors on top.
Phase detection was done by a Miller integrator circuit "Phantastron"
which created a slowly increasing voltage or ramp which delayed the
firing of two monostables. These monostables "gated" (logic was
called "pulse technique" in those days) the returned pulses,
switching the phantastron from a rising to falling ramp or visa versa
so that the phantastron voltage tracked and could be used as the time
of flight distance from the beacon. A missing pulse circuit left the
phantastron in a static condition until pulses arrived or the timeout
circuit reset and the scan from zero delay would start again.
Some elements of these ideas are still probably useful,
cheers, Neville Michie
On 13/07/2008, at 6:43 PM, Hal Murray wrote:
> I found this interesting. It's a chunk of the memoirs of a Coast
> Captain who was in charge of Loran in Japan from 1961-1964.
> It's half Coast Guard history/nostalgia, half his memories of
> Japan, and a
> little bit of Loran. But I thought that little bit was neat.
> How good were crystals back in WW II time frame?
> Does anybody know anything about early Loran? I'm guessing that the
> secondary stations listened to the primary and sent their pulse X
> microseconds after they heard a pulse. How did they implement that
> What sort of filter/PLL did they have on receiving the primary
> What is current Loran navigation accuracy? What was it like in the
> old days?
> These are my opinions, not necessarily my employer's. I hate spam.
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