North Australian FISH FINDER TM forums

Hey Balou, all of your Fog Bay marks will be the same too. When I brought a new GPS I left the old one in the boat and used both of them at the same time till I had all the marks in the new GPS, took a while. I know your old one went with the boat you sold.

Balou

I've sent you a pm.

Your old data looks like AGD66 datum.

Your old Garmin info gives a position 220 metres s/w of the HDS10.

When I put the Garmin data into a datum converter, nominated it as AGD66 datum and hit the "convert" button; it comes out as .............the HDS data you gave me which is on WSG84 datum!!.

I won't put the google earth shot up here as I think its one of your secret squirrel spots.

I've had a look at the datum selection in the HDS operations manual. It tells you how to change datums but it doesn't tell you what the selection is or if AGD66 is one of them.

Maybe u can check it out on the HDS10 chart menu??

If it is, just change your datum from WSG84 to AGD66 but you'll have to be careful about GPS info in the future 'cos u'll be 220 metres different to everybody else.

Another way is to convert all of your spots to WSG84 individually. How many spots have u got to convert? U can get a pretty good converter off the web for $5 download. Or if $5 is too expensive get 4-5 free trial goes per visit and do them over time.

I didn't play around with the converter as it was in Universal Transverse Mercator (UTM) configuration. I just used google earth to convert your data (both lots) to Eastings and Northings and then did the conversion on a free trial.

I'll tell you one thing though. U'll know a lot more about charts and datums when u've finished.

Google earth is your friend.

Mate I'd convert 2 or 3 more and go out and try them first to make sure u get the right result before undertaking a big conversion job maybe unnecessarily.

Or if u like, pm me with some more of your old Garmin stuff and I'll do it for you.

well done ron, how are you going these
days.

Double post

I will put an even weirder one forward. 10 weeks or so ago, had some visitors up, strong wind warning so we go to Bynoe for a few days, crabbing for the first one and then fishing the afternoons out the front and camping up in Tapa Bay of a night eating crabs, great time. Got going a bit late on the friday and set the last half of the pots in the dark in Madford inlet. The big boat has 2 x Furuno GP7000 GPS units in it they have never missed a beat in 2.5 years, and are interconnected, save on one save on both but with two areials, quite a good back up if you are closing on the coast line at any speed. Once it got dark, I think, well I have all the crab pot drains for Bynoe saved in the maggellan handheld that I use in the little boat so I forage around in the cabin and dig it out. It takes a fair while to aquire and ultimatly dosent, next thing, the first furuno loses its position fix, 3minuts later so does the other. Its no brainer so down there so no great stress but a bit disconserting to think that 8k worth of gear has just shut down. I reboot and one is a goer for about a minute and a half, but still no fix with the handheld so I turn it off. We are wondering if we should just anchore up and drink all beverages in esky in case nuclear war has broken out and the system is off tap. Within seconds of shutting the maggellan down both furunos are on line, WTF. Tested it 4 times that night and later in the weekend, same every time the 250 maggellan was on the 2 x 4k furunos went down. I was surprised as I thought they were only receivers, that maggelan must transmit or at least emit somthing becase the furunos didnt like it thats for sure.
I am sure Ron can sort it out for me, perhaps a site inspection and on water trial may be required though!!.

G'day Andy

Going OK

Am rethinking Roper following the Limmen Bight National Park news. So far, Limmen River fishing camp looks the go but its early days.

Get yourself some time off and join us.

WRT the GPSs, the frequency the satellites transmit on is 1575.42 mhz.

The GPS receiver generates a local oscillator freq which converts the satellite frequency to a processing frequency inside the GPS receiver.

The internal processing system in a GPS receiver generates more oscillator frequencies during its process as well.

All of these spurious emissions from the various processors are low level but even that low level is sufficient to knock out a satellite signal.

In your case it sounds like that was what was happening with the Magellan. Generating " spurious emissions" (called birdies in the industry) 1 of which popped up on a freqiuency which (when mixed with a birdie out of the Furunos) would knock out either the satelllite signal or the Furuno processing system.

In this case I think that the Magellan was generating a birdie that mixed with a furuno birdie to produce the satellite freq, or the Magellan birdie/s simply got into the Furuno processing chain.

Was the Magellan knocked out?

I'm sure they will all work ok with sufficient separation.

Solution is to get physical separation of the Magellan from the Furunos. Depending on how strong the birdie in the Magellan is it might be a few metres or more.

Never mind the crocs, ya just gotta watch those darned birdies!!!

Interaction between receivers.

I used to use that habit of receivers generating birdies to find receivers associated with illegal transmitters.

So the GPS problem you describe is not new. Far from it.

Mate be more than happy to do site site inspection and on-water trial.

Thanks Ron...

I appreciate the time you spent working through this equation. I know it must not have been easy as I 've been on google since Saturday night trying to figure this out and working backwards through all the formulas.


After I replied to your PM the bloke from Garmin rang me back . I told him the model number and the year of the sounder etc. He believes there's a very strong possiblity that the sounder is set to Aus Geod 84. (agd 84?)

Do you know if difference in meters between AGD 64 and AGD 84.

There was 500 marks on my old sounder but I wrote down about 120. I plan to get one of those garmin hh etrex and change the setting to AGD 66 and mark them on my new Lowarnce set on Wgs-84.

I was told that if I change my lowrance setting to AGD64 put all my marks in and then change it back to WGS-84. The marks will will automatically covert over from AGD 64 to WGS84.

Once again thank you.

Hi Anth0ny

The datum AGD66 and AGD84 were datums ad0pted in Australia in.............wait f0r it................1966 and 1984...surprise....surprise!

They are 0nly ab0ut a metre apart. I was trying t0 keep it simple by 0nly talking ab0ut AGD66.

H0wever there is a difference between WGS84 (which is what y0u want) and AGD66/AGD84 0f ab0ut 200 metres in a n0rtheast/s0uth-westerly directi0n.

S0und familar fr0m the G00gle Earth image 0f the Garmin GPS data y0u sent me sh0wing 220m difference in th0se same directi0ns?

In y0ur last sentence y0u talk ab0ut AGD64. I guess y0u mean AGD84.

That advice s0unds reas0nable but can I suggest that y0u d0 it with the Garmin data that yu0 sent t0 me first? See if the result y0u get = the HDS10 result that yu g0t 0ut 0n the water?

If s0 then d0 the rest.

Pretty interesting stuff would this effect the marks in the Fff magazine if they have all been taken on different gps ?? I remember someone a while ago commenting on them saying there was nothing on a few of the marks think at mouth of south alligator
Ronje what would be the maximum distance a waypoint could be out over from one setting to another?? Pretty dangerous really

Sorri Doug

Get back to ya shortly with an idea.

Doug

See attached.

Its a mark at 12 28 4.88 secs south and 130 50 13.66 secs east based on WSG84 datum

There is a mark that says WSG84 which is the datum we want.

The other marks show the same place but using the WSG84 lat/long converted to AGD 66, AGD84 and GDA 94. In different colours.

So, if you were using a GPS on datum AGD66 and punched in the above lat and long u would end up at the end of the blue line marked AGD66 203 metres away.

If u were using a GPS on datum AGD84 and punched in the above lat and long u would end up at the end of the red line marked AGD84 215 metres away.

Make sense?

Matt book is in WSG84. Maybe the other fellas weren't?

Most likely error due to datums that u'll come across in Aus is about 220m.

Hello all

Here's a useful link that explains the GPS receiver questions.

http://www.yachting.org.au/site/yachtin ... sheets.pdf

The link goes to an Australian Maritime Safety Authority (AMSA) Fact sheet which explains it all. There are 17 pages but first couple lay out the problems u'll be interested in.

The golden rule is to make sure the GPS datum in your is WSG84 even if the h/book says that's the default setting.

A very handy tool is to make sure that the compass heading in your GPS is set on "TRUE" not MAG.

Then your track can be put on/taken off a chart without having to be converted (nautical charts have a True north datum).

The HDS 10 does do an automatic convertion from one datum to another. Set it on AGD 64 and enter the marks. Once they are all entered change the datam setting back to WGS84. The conversion will be made for you Balou. Too easy when you know the old Datum you were using and the datum you want them all to be.

Nice work Ronje working out which datum Balou was previously on!

sounds like you had by a few beverages for the man Balou! :

Most of the older style charts were in AGD66. Some of them still in use too.

U're right with the advice.

I guess the proof will be if/when he enters the data in 66 and then does a bulk conversion by swapping to WSG84 (If he can then find his secret spots).

I've seen lots of secret squirell marks lost because people don't understand the map datums.