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Author Topic:   grounding for loran
njboland posted 11-12-2002 03:27 PM ET (US)   Profile for njboland   Send Email to njboland  
Greetings! I want to install a loran for fishing on my '86 Montauk. Where should I hook up the ground wire? It is my understanding that for loran to work correctly a good ground is necessary. Thanks in advance. Nick
Drisney posted 11-12-2002 05:11 PM ET (US)     Profile for Drisney  Send Email to Drisney     
Nick, I attached the ground to my engine.(run through the tunnel) But the trick deal involves the antennae; attach a wire from the coupler to your console rail. It works perfectly and you have one less antennae to interfere with fishing. Dave
njboland posted 11-12-2002 05:17 PM ET (US)     Profile for njboland  Send Email to njboland     
Thanks for the advice Dave!!
triblet posted 11-12-2002 11:31 PM ET (US)     Profile for triblet  Send Email to triblet     
Why bother in this day of GPS? More
repeatable and more accurate than LORAN.

But Drisney's right on, those low frequencies
don't need much of an antenna, as long as
they have a GOOD earth (i.e water) ground.
DGPS is down in the same frequency range,
and my DGPS never worked well on the trailer
(no earth ground) but worked just fine in
the water, even after I broke off the antenna


njboland posted 11-13-2002 12:56 PM ET (US)     Profile for njboland  Send Email to njboland     
Triblet - The only reason for the loran is fishing as I have a hand held gps that I use for nav. Do you believe that todays gps gives you as good or better repeatability as loran? The other problem is that my "numbers" are all loran numbers, so the only way I can figure to convert them is to run the loran and gps side by side as the mathematical conversions are not accurate. Would be interested in your thoughts. Nick
Tom W Clark posted 11-13-2002 01:35 PM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     

There is no question that GPS is more accurate and precise than LORAN. When Selective Availability (S/A) was turned on, GPS was comparable but still usually better than LORAN.

Now that S/A is turned off, GPS is far more accurate than LORAN. Many GPSs now also use the Wide Area Augmentation System (WAAS) or Differential GPS (DGPS) technology to refine the accuracy of GPS even more.

There's nothing wrong with using a LORAN mind you, it could be argued that having redundant position locating devices is a safety advantage, but if you already have a GPS, then use that and save yourself the hassle, expense and space of installing the LORAN.

Don't let your way points slow you down. Unless your LORAN is ancient (like from the 1980's) it should be able to display your way points in either Time Difference Lines of Position (TD's) or as Latitude/Longitude coordinates just as your GPS does. Go through the menu on your LORAN and you will probably find a "toggle" to switch from one to the other.

Be sure to pay close attention to whether you are displaying Latitude/Longitude in Minutes and Seconds or Minutes and 1/100ths of Minutes (decimals) when you copy your way points to the GPS. This often leads to confusion.

As crazy as this sounds, even our own military does not use a standard on this. The Navy uses Minutes and Seconds but the Air Force uses Minutes and 1/100ths of Minutes. (say again where you want that bomb dropped...)

njboland posted 11-13-2002 05:58 PM ET (US)     Profile for njboland  Send Email to njboland     
Wow. I am glad that I posted this topic. It is helping with my November blues! Tom, my Loran set on my other boat is a Sitex EZ 97. I do not know how old it is, but I would guess at least early 90's and possibly older. I am able to display the coordinates in Lat/Lon, BUT, it is my understanding from what I have read that the Lat/Lon indicated by a Loran set is some sort of mathematical calculation that is not an accurate representation of the true fix. Simply put, it is my understanding that the Lat/Lon supplied by a loran set is only an approximation of the true Lat/Lon fix.

That being said, I am glad to hear that GPS is hands down more accurate than Loran. My only reason for doing this, as stated, was because I have a book of loran numbers for fishing spots. I want to "transfer" those numbers into gps coordinates (ie, Lat/Lon) and do not know of a way to do this accurately save for running both machines simultaneously and marking the Lat/Lon on the GPS when the loran numbers are correct. My GPS is a handheld Garmin 48 that I love and that has proven to be fairly accurate from a repeatability standpoint. So, how do I get the loran numbers into my GPS unit so that thay are accurate unless I run both at the same time, which for me is a problem as I do not have Loran on my Whaler, rather it is on another boat I have. Thanks for all of your input and thoughts! Nick

lhg posted 11-13-2002 07:24 PM ET (US)     Profile for lhg    
Loran? What's that? I don't think it's long for this world, as the Coast Guard is now fully operational nationally with the DGPS towers. Plus, there is the WAAS, but evidently is is not as accurate for land based vehicles as the DGPS.

I also learned that Loran Lat/Lon readings are not accurate. Some of my transfers to DGPS were as much as 2 miles off. I think the only thing you can do is go to the Loran position, and then save in place on your new DGPS.

dfmcintyre posted 11-14-2002 08:50 AM ET (US)     Profile for dfmcintyre  Send Email to dfmcintyre     
Nick -

I'd second what Larry posted, i.e. best way is to take out your portable on your other boat, and when the loran is on location, note the L/L on the GPS, and create a waypoint on the GPS.

I'd also double check the L/L readings between the two. You might find out that it is a more accurate reading between the two then you had origionally assumed.

If you took off the loran unit, and jury rigged it on the whaler, especially using your rail as an antenna, I think that you would introduce a variable in the reading, and that you'd be off position with the loran, and have a problem.


jimh posted 11-14-2002 09:09 AM ET (US)     Profile for jimh  Send Email to jimh     
njboland writes:"it is my understanding from what I have read that the Lat/Lon indicated by a Loran set is some sort of mathematical calculation that is not an accurate representation of the true fix. Simply put, it is my understanding that the Lat/Lon supplied by a loran set is only an approximation of the true Lat/Lon fix.

Both LORAN and GPS deduce or calculate a position from other observations. The fundamental approach is the same: they both measure distance from a remote, known location (the transmitter site) by careful measurement of time intervals between the arrival of radio signals from several different sources.

In the case of LORAN, the signals are travelling over the earth via ground wave propagation, as thus the speed at which they propagate is subject to some variation from influences of terrain, ground conductivity, etc.

In GPS, the signals travel only through the atmosphere, and thus their speed is more constant, although in high-precision sets this is also compensated.

To determine the location of the transmitters is quite easy for LORAN. They don't move. They're in a fixed location.

The transmitters for GPS are satellites orbiting the earth, and their location is only known from precise data about their orbits and from precise time keeping. (A GPS is also the world's most accurate time piece--it has to be or it could not be a GPS.)

Once the location of the transmitter is known, the GPS works out its position just like the LORAN set, by measuring time intervals and solving for a position where such time intervals could uniquely be observed.

In both techniques there is very clever mathematics involved, probably more in the case of a GPS than in a LORAN. I say that because LORANs have been able to compute their positions with the fairly simple microprocessors of the 1980's. A GPS needs much more computer horsepower, in part because it has to first compute the location of the transmitters it is receiving, then deduce its position. The LORAN can be preloaded with the transmitter locations, since they are not moving.

bsmotril posted 11-14-2002 10:43 AM ET (US)     Profile for bsmotril  Send Email to bsmotril     
Most of the newer GPS will also display TD and let you enter in old waypoints you may have in TD format. I have done that with my Raytheon GPS and found it is very accurate in it's conversion process getting me within 50-75 yrds of the old TD formatted waypoint in every case I have tried. This is on the TX gulf coast, and accuracy might vary in other areas depending on the crossing area of the TD lops,
newt posted 11-14-2002 11:34 AM ET (US)     Profile for newt  Send Email to newt     
JimH, interesting info on GPS, etc. I always thought (incorrectly) that GPS worked similarly to surveying instruments, which is as follows:

With an EDM (electronic distance measurement), which is used solo or coupled with a theodolite (making it a total station), the distance is calculated based on a series of different wave length signals, and how far out of phase they are.

So, the EDM sends out a signal with a wave length of say 1000 feet. When the signal returns, the distance is calculated to the nearest 1000 feet based on the phase of the return signal. Simultaniously, a 100' wave is sent and distance narrowed to the nearest 100', then 10', 1', 1/10', 1/100', and 1/1000'. The accuracy is amazing... distances of miles can be measured to 5/1000's of a foot (1/16")!

I wonder if the same technology will eventually be used for GPS?

bsmotril posted 11-14-2002 10:05 PM ET (US)     Profile for bsmotril  Send Email to bsmotril     
That technology is not really practical for satellites moving at tens of thousands of miles per hour. They are not geostationary. As a result, you have a lot of phase shift due to doppler shift as the satellites move towards you, then away. BillS
SSCH posted 11-14-2002 11:16 PM ET (US)     Profile for SSCH  Send Email to SSCH     

I think you may have point in that the conversion of TDs to Lons and Lats for your GPS will be problematic.

I agree with almost everything said, but.....
Loran had great repeatability (sp?) but not good absolute accuracy. The Lons and Lats from your old waypoints may be way off the true numbers. If so, your very accurate GPS will be at the true locations you input, not your waypoint location. The only way to easily transfer points is to establish an error correction factor for your old unit. Very few of us ever bothered to do that. Even if you did (or do), the correction factors vary over distance, sometimes. For those who remember the old ASF charts you know what I mean. Loran signals are effected by the electrical resistivity (actually the permeability, which is related to resistivity) of the path between the transmitter and the receiver. When only water is between you and the source, Loran is at its best. If the transmitters have to send a signal across much land, you'll have large ASFs (correction factors).

triblet posted 11-14-2002 11:48 PM ET (US)     Profile for triblet  Send Email to triblet     
Yes, I beleive GPS today is more accurate and
repeatable than LORAN. GPS with WAAS is
9' accuracy and about the same repeatability.
Without WAAS or DGPS, the highest number I
hear anyone putting on the accuracy is 45'.
Some are claiming 20-30'.

I'd enter all your LORAN waypoints into your
GPS using the GPSs TD conversion feature.
The clinker is that while LORAN was quite
repeatable, it's absolute accuracy wasn't
very good, so the lat/lons you get in the GPS
won't be very good. From the CG website:
> Loran-C provides better than 0.25 nautical
> mile absolute accuracy for suitably
> equipped users within the published areas.

A quarter mile isn't too hot. But LORAN is
consistently wrong, so it's quite repeatable.
So why put this in your GPS? Because some
day LORAN is going to go away, and if your
LORAN unit dies before then, you can switch
to the GPS. You'll quickly figure out what
the error in a given area is, and be able
to find the spots using the GPS and a little
Kentucky windage.

I'd put the LORAN waypoints in the GPS with
some naming convention like L_HOTSPOT where
the L_ indicates it came from the LORAN.
Each time you go to a spot, put a new
waypoint in the GPS without the L_, and
delete the L_ waypoint, that way you can
keep track of which ones you've fixed.

Larry: WAAS, IF you can get the bird, is at
least as accurate as DGPS. Problem is the
birds are fairly low (about 14 degrees above
the horizon in NorCal) in some areas, and
it's easy for them to go behind a hill, or
even a tree.


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