Gps accuracy
Submitted by Bodgy 79 on Sat, 2025-03-08 10:17
Gday all,just seeking info on external gps antennas.
Using a hds 12 just for a plotter that is flush mounted in a plate cuddy cab with soft top & clears.it's a new unit and doesn't drop out with sats but the waypoint I'm trying to line up for a fish seems to bounce around alot as soon as its zoomed in to about 20m or less.Is this just processing a bit slow because of its mounting and would an external antenna help this and become more accurate?
cheers
Rob H
Posts: 5822
Date Joined: 18/01/12
Soft top shouldn't bother it
Soft top shouldn't bother it at all.
Its not a conspiracy theory, but the US mucks around with GPS accuracy (or certainly used to) called SA? from memory selective availability, I thought Obama stopped it?
During times of war around the globe as they choose to reduce accuracy as it's so easy and cheap to use for very accurate military use.
With the present situation it's amongst the less unbelievable things happening in the USA
Give a man a mask, and he'll show you his true face...
The older you get the more you realize that no one has a f++king clue what they're doing.
Everyone's just winging it.
squalis
Posts: 138
Date Joined: 23/11/14
gps
Use an external gps antena mounted horizontally above the soft top area of your boat, it will have a full sky view and will receive postioning data from all satelites in view up to the horizon. Use a rail mount. Your flush mounted Lowrance hds units built in gps antena will not see all satelies available as it is mounted inclined in your dash area and my have the inbuilt antena partially obscured by the fibreglass surroundings consequently it will have inaccuracies or loss of accuracy in positioning and location of fixes . Any waypoint entered and stored in your Lowrance will have been recorded with partial resolution geometry and wont be as accuate as it could be with an all sky view using all satelites visable .Its not the soft top thats the prolem your instalation of the lowrance that is the problem,the mounted inclined lowrance that is not vertical is the origin of your positioning problem. If you are interested i have a spare Lowrance gps antena that you can connect via your NMEA port on your Lowrance. I will sell it to you at half the new price. I purchased a satelite compas gps antena for ultimate accuracy and have no need of it any more. The higher number of satelites that can acessed the higher the accuracy of your positioning. Its all about resolution geometry. If your lowrance unit was cradle mounted horizontaly you woud not have this problem.Ii have been involved in comercial survey and positioning for 40 years.S.A or Selective Availability is not currently in operation.