Time Signals
Jul 17th 2011, 2:36 pm
#16
Joined: Jun 2011
Location: In the middle of 10million Olive Trees
Posts: 12,053
Re: Time Signals
There was a "work around" for some time called "differential GPS. That worked by a fixed land station with an exactly known location, receiving the GPS position, comparing it to the actual position and then transmitting the "error" by radio to the special DGPS receiver which corrected their received signal using the broadcast error hence getting the true position.
It only lasted for a couple of years before the US turned off the wobble and the DGPS receivers became redundant.
There are special techniques for averaging out the received position to get a more accurate position.
You mention LORAN. I never tried that but in the 80's I had a small yacht version of the Decca Navigator - like the system the fishermen used and that was very good - better than the alternative "Satnav" system that existed at the same time.
Interesting memories!
It only lasted for a couple of years before the US turned off the wobble and the DGPS receivers became redundant.
There are special techniques for averaging out the received position to get a more accurate position.
You mention LORAN. I never tried that but in the 80's I had a small yacht version of the Decca Navigator - like the system the fishermen used and that was very good - better than the alternative "Satnav" system that existed at the same time.
Interesting memories!
Jul 17th 2011, 2:47 pm
#17
Joined: Jun 2006
Location: Granada Costa
Posts: 10,904
Re: Time Signals
GPS on yachts is far better than a Tom Tom - they interface with the autopilot and you can set a complicated route and let it do all the work.
One day cars will be like that!
And no - none of this is off topic as they all rely on time signals!
Jul 17th 2011, 2:51 pm
#18
Lost in BE Cyberspace
Joined: Feb 2007
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Re: Time Signals
Being old I can use a sextant but never had a very accurate timepiece
Jul 17th 2011, 2:59 pm
#19
Joined: Jun 2006
Location: Granada Costa
Posts: 10,904
Re: Time Signals
I don't remember Omega but Decca gave a continuous position which is why it was so much better than Satnav.
Jul 17th 2011, 3:35 pm
#20
Lost in BE Cyberspace
Joined: Feb 2007
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Re: Time Signals
http://en.wikipedia.org/wiki/Decca_Navigator_System
Omega was a long range radio positioning but was more widely used in aviation.
Jul 17th 2011, 3:54 pm
#21
Joined: Jun 2006
Location: Granada Costa
Posts: 10,904
Re: Time Signals
The odd thing with Decca was that because the signal had fixed errors you could buy special "Decca" Admiralty charts with lots of overprinted squiggly lines on them to give you a more accurate position.
I seem to remember that they were a tad expensive! But then the Decca Yacht Navigator was a snip at £2000 - in 1980!
I seem to remember that they were a tad expensive! But then the Decca Yacht Navigator was a snip at £2000 - in 1980!
Jul 17th 2011, 4:17 pm
#22
Joined: Jun 2011
Location: In the middle of 10million Olive Trees
Posts: 12,053
Re: Time Signals
Omega was a US proprietary system operated by their coastguards in the early 1970's in certain "convenient" places in\around US countries of influence.
As they operated at much low frequencies than those used by other systems the transmission was nearly all ground wave, no sky wave, so when when it was pensioned off (about in the mid-late 90's) some were converted to "other use" - such as submarine communications.
As they were all ground and no sky the frequency was also very accurate at long distances
Remember the "Luxembourg effect" where it faded in and out ? That was caused by the sky wave nulling out the ground wave
As they operated at much low frequencies than those used by other systems the transmission was nearly all ground wave, no sky wave, so when when it was pensioned off (about in the mid-late 90's) some were converted to "other use" - such as submarine communications.
As they were all ground and no sky the frequency was also very accurate at long distances
Remember the "Luxembourg effect" where it faded in and out ? That was caused by the sky wave nulling out the ground wave
Jul 17th 2011, 4:18 pm
#23
Joined: Jun 2011
Location: In the middle of 10million Olive Trees
Posts: 12,053
Re: Time Signals
The odd thing with Decca was that because the signal had fixed errors you could buy special "Decca" Admiralty charts with lots of overprinted squiggly lines on them to give you a more accurate position.
I seem to remember that they were a tad expensive! But then the Decca Yacht Navigator was a snip at £2000 - in 1980!
I seem to remember that they were a tad expensive! But then the Decca Yacht Navigator was a snip at £2000 - in 1980!
