[time-nuts] Time transfer, internationally before GPS
eb4apl at cembreros.jazztel.es
Tue Mar 4 14:06:31 EST 2014
Since the original question was about alternatives to the traveling
clock method before the advent of GPS, I remember two that were used by
NASA to check the synchronization of their Deep Space Network facilities
around the world.
- Moon bounce: A PN code was modulated on a microwave signal that was
sent from the Mohave desert (there were a suitable transmitter - antenna
there) to the Moon and its reflection was picked up in the facility to
be synchronized.. To simplify the receiving equipment the code was
continually compensated for the varying round trip distance between
stations and it was correlated with a ramped model in the receiving
end. The output was drawn on a strip chart recorder and some
interpretation was needed to estimate the clock difference. The
accuracy was said to be about 1 us but the system was not very popular
within the transmitter and the receiver crews.
-VLBI: Among other observables, VLBI can be used to get very good
estimations of the clock difference between stations.
A traveling clock was also used, there were lots of stories of afraid
pasengers traveling close to the "Atomic Clock " and for making the
thing more frightening it was a HP Cesium with the Patek Philipe analog
clock in the front conspicuously ticking. They were assured that it was
not an "Atomic Bomb" !!!.
On 04/03/2014 4:23, Bob Camp wrote:
> One of the early relativity confirmation experiments was done with very similar clocks before that film clip was made. There were a number of corrections made as part of the trip. One of them was to re-confirm the traveling Cs once it got back to it’s starting point. You only could “use” the trip if the Cs came back home still on time.
> There were a *lot* of satellite time transfer experiments in the 60’s and 70’s. They worked well enough to reduce the frequency of clock trips, but not well enough to eliminate them. The GPS common view stuff was the first approach that (with proper calibration) got them to a better level of time transfer than a clock trip.
> On Mar 3, 2014, at 9:50 PM, Max Robinson <max at maxsmusicplace.com> wrote:
>> The piece didn't say anything about correcting for acceleration.
>> Max. K 4 O DS.
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>> ----- Original Message ----- From: "Jimmy Burrell" <jimmydburr at gmail.com>
>> To: "Discussion of precise time and frequency measurement" <time-nuts at febo.com>
>> Sent: Monday, March 03, 2014 7:17 PM
>> Subject: [time-nuts] Time transfer, internationally before GPS
>>> My apologies to the list if this has been posted before but I found it fascinating. I'm guessing this was early 60's.
>>> I wonder if this practice continued until the advent of GPS? I be interested to know if there was an interim technology and what it was.
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