In a world before GPS - Page 1
Forum section: electronics / general

author: watchmaker
author_rank: Unknown
timestamp: January 31, 2024, 05:14:39 pm
content: There was this.This is what passed for the best oscillator before GPS, and even surpassing quartz. I just restored this 1895 marine chronometer and thought it might make a topic of interest.While I have customers send me only the brass cased instrument, they were housed in exquisite boxes of mahogany (real) or rosewood.To obtain best precision, they were mounted in gimbals to keep them horizontal. They were wound by the same hand every day at the same time and this was reported to the ship commander under penalty of courts martial.Greatly oversimplified, the chronometer told you the time in Greenwich England. It generally had an error rate of less than 2 seconds per day; but it was precisely two seconds per day and maintained that precision for at least three years. Then sent for service, which explains the condition after 130 years.Your sextant told you what time it was where you were. The time difference told you how far around the globe you were from Greenwich (1 hour equals 15 degrees).Ships, particularly military ships, carried 3. If you had one and it went out your SOL. If you had two and one went out, you did not know which to trust. With three you trust the two that behaved.In practice, the mean for the three dial readings was used for each position shoot.The search for the perfect oscillator drove materials science, leading to the 1922 Nobel Prize for physics for Elinvar and Invar.The USN did not stop using mechanical chronometers until GPS was up and proven; recalling the WWII Hamilton M21 from the fleet in 1988. Quartz had been issued to three ships in WWII but the USN was never happy with it as a primary instrument because of vibration and salt. Today the Naval Academy is trying to buy them back to teach navigational skills again (EMP?)

author: RoGeorge
author_rank: Super Contributor
timestamp: January 31, 2024, 08:17:11 pm
content: Wow, thanks for the great pics and story.These reminds me of that documentary series from the 70s or 80s, about the struggle for inventing any device or method that can help ships finding their position on the map, such that they won't get lost at sea while crossing the oceans.

author: fourfathom
author_rank: Super Contributor
timestamp: January 31, 2024, 08:30:10 pm
content: Quote from: RoGeorge on January 31, 2024, 08:17:11 pmThat documentary is "Longitude", based on the book of the same name by Dava Sobel. Both the book and the mini-series documentary are brilliantly done -- I re-read and/or re-watch these every few years. The video is available for streaming on Amazon, and I see there is a reduced-resolution copy on Youtube.Highly recommended.And yes, I have used a sextant at sea (for fun).

author: pdenisowski
author_rank: Super Contributor
timestamp: February 01, 2024, 12:43:48 pm
content: Those are gorgeous - thank you for posting them!Whenever I present on GPS, I always start out by saying that GPS is really abouttime, not position. I don't think most people realize the critical role that GPS plays in providing a common, stable time.Quote from: watchmaker on January 31, 2024, 05:14:39 pmOr even something as simple as denying GPS. I remember talking many years ago to the US Coast Guard about their interest in re-introducing LORAN (eLORAN), in part because it's extremely difficult to jam. Apparently they're still interested:https://www.usni.org/magazines/proceedings/2021/june/let-coast-guard-operate-eloran

author: 5U4GB
author_rank: Super Contributor
timestamp: February 01, 2024, 01:02:33 pm
content: Quote from: fourfathom on January 31, 2024, 08:30:10 pmIf you want an updated form of that, I can recommend "Inventing Accuracy: A Historical Sociology of Nuclear Missile Guidance" by Donald MacKenzie.

author: watchmaker
author_rank: Unknown
timestamp: February 01, 2024, 03:43:54 pm
content: Actually, Sobel got almost all her information from a symposium held at Harvard to celebrate the anniversary of Harrison. She was there as a reporter for the Harvard Alumni magazine.You can obtain the source material from NAWCC in their publication of the proceedings. You will find me in the list of subscribers.This was a two day international event with presentations covering the costs of pre chronometer navigation to the impacts afterward. I was invited because of some research I did on technical balances and was seated at dinner with the likes of David Penney, Catherine Cardinale, Jonathan Betts and Anthony Randall. Kept my mouth shut.If you can find a copy of the Proceedings, it is well worth having. It was illustrated by David Penney who did the postage stamps and is a well known horological illustrator.In my opinion, there is a reason you have not heard of Sobel since. But I know some of the "dealings" that went on and I have my views of her.

author: fourfathom
author_rank: Super Contributor
timestamp: February 01, 2024, 06:56:26 pm
content: Quote from: watchmaker on February 01, 2024, 03:43:54 pmThanks for the info. But I probably don't need to know "how the sausage was made", Sobel's book is still very readable and enjoyable.

author: watchmaker
author_rank: Unknown
timestamp: February 01, 2024, 07:16:39 pm
content: Quote from: fourfathom on February 01, 2024, 06:56:26 pmGood on ya! But you are not the only reader.

author: watchmaker
author_rank: Unknown
timestamp: February 01, 2024, 07:22:49 pm
content: Quote from: pdenisowski on February 01, 2024, 12:43:48 pmA friend/customer is the astronomer/physicist who manages the rubidium fountain at the USNO. Civilization collapses without that. He took us on a tour and also explained to us that he has been fighting the Chinese for over 10 years.

author: JimboJack
author_rank: Regular Contributor
timestamp: February 06, 2024, 12:12:45 am
content: Many years ago,A Navy tested jamming GPS on the east coast of USA,side effects alot of exchanges stopped working and electronic HF traders could not trade as there time stamps were out.

author: RoGeorge
author_rank: Super Contributor
timestamp: February 06, 2024, 06:47:35 am
content: This reminds me of at least one story from the recent years, in which a ship was silently detoured by spoofing the GPS signals. The crew didn't realize, and sailed the ship near some pirates vessel, where it was captured.I wonder if modern ships still keep a sextant onboard, and if anybody ever double check their GPS coordinates by traditional methods.

author: fourfathom
author_rank: Super Contributor
timestamp: February 06, 2024, 07:27:26 am
content: Quote from: RoGeorge on February 06, 2024, 06:47:35 amWhen long-distance ocean sailing (sailboat) I've kept a sextant and chronometer and almanac / tables in board and would occasionally take a test fix to make sure I still knew how.And I've seen relatively small errors in ship radio position reports (AIS), of a mile or so off This wasn't due to a GPS error, but to an error in ship navsystem configuration, where the GPS data was "corrected" to fit the chart chart datum, and that "corrected" position was reported via the AIS signal. It was disconcerting to have my chartplotter show a ship passing one mile to my south, when my eyeball saw it passing one mile to my north. Always trust your eyeballs!I told this story to a Coast Guard officer, during a visit to the San Francisco Vessel Traffic Services center, and he told me about a time when according to the AIS system a number of ships apparently simultaneously drifted several miles from their moorings (but the radar plots had then un-moved). Turns out that these ships were using a GPS satellite that had gone out of service and somehow that screwed up their position. Other ships has updated GPS configurations and didn't have this problem.And a few times sailing out of Hawaii when the Navy was running exercises they would do something that would screw up local GPS performance. They did announce this ahead of time ("notice to mariners") so at least we weren't taken by surprise.

author: forrestc
author_rank: Unknown
timestamp: February 06, 2024, 07:51:25 am
content: Quote from: pdenisowski on February 01, 2024, 12:43:48 pmOr that measuring the relativetimingof signals is what permits the "Position and Navigation" part of a PNT system to work.Quote from: pdenisowski on February 01, 2024, 12:43:48 pmThere are currently (last I was aware of) three eLoran test stations running in the western US - Fallon, NV; George, WA; and Havre, MT. I've heard that they plan to continue these through at least 2024, maybe 2025.There is a LOT of discussion in the PNT community about a secondary alternative to GPS/GNSS for time distribution. The increased occurrence of GPS jamming and the criticality of GPS for this purpose has made a lot of people start thinking about this.

author: pdenisowski
author_rank: Super Contributor
timestamp: February 06, 2024, 11:52:54 am
content: Quote from: forrestc on February 06, 2024, 07:51:25 amI haven't been active in the PNT community for a while, but I remember there being a lot of interest in Iridium's STL at one point. And the taboo about using "other" GNSS systems (i.e. GLONASS) also seems to be slowly going away.It's interesting to me how people are only now realizing the vulnerability of satellites (to both natural events and "bad actors"). Something similar has been happening in communications, where there has been a resurgence in interest in HF as a backup to SATCOM.A webinar I did on this for the Associate of Old Crows (the EW folks):https://crows.site-ym.com/general/custom.asp?page=LostArtofHF-ondemand