Hello all,

When you network two lowrance HDS units, one bow and one at the wheel, where do they base their coordinates off of?  Does each use its own seperate antenna?

Say I mark a waypoint on the console directly over a brush pile.  I then go to look at it on the bow... is the bows position to the brushpile correct or did it create its own position at its point, different from the coordinate of the console?

The way I understand (and the only way that makes logical sense) is that they simply share the original marked coordinate, and each unit's distance from that coordinate is different and based off of that individual units curent position... not which one it was recorded on.... correct?

Considering even with WAAS correctional positioning, it is still only accurate to 3 meters (10 feet). So if you set a waypoint, it will only give it to you within around 10 feet of where it was placed, not the exact location. Usually that is where the real time sonar comes in so you can locate the same structure and move a few feet whatever direction you need to. With networked units, I am not sure which unit takes the "lead" role to display locations...

100 meters: Accuracy of the original GPS system, which was subject to accuracy degradation under the government-imposed Selective Availability (SA) program.

15 meters: Typical GPS position accuracy without SA.

3-5 meters: Typical differential GPS (DGPS) position accuracy.

approx. 3 meters: Typical WAAS position accuracy.

Note: if your unit does not have WAAS correction, then it will be within 10-15 feet depending on the GPS signal that day.

Each HDS Unit has an integrated GPS module. When you mark a waypoint, the cords will be based off of the location of the headunit used to create the waypoint.  At least that is my understanding.

  When I mark something, I typically use the waypoint as a general point of reference.  Due to margin of error, drift path, etc... it may take me a minute or so to locate a specific piece of cover, especially if its in deeper water.  I normally try to have a visual reference if the piece of cover/structure is something I find relevant/useful.

  I've had both bird and lowrance units on my current rig, and I have yet to notice a difference in GPS accuracy between the two.  Granted I haven't used my new HDS units much and they're based of the new 4000 series antennas which are suppose to be a bit more accurate than the older 3000 antennas.

dick, assuming both head units are networked to the same antenna, wouldn't the displayed coordinates on each unit be the coordinates of the antenna?  I know I'm splitting hairs due to the inherent inaccuracy of GPS in general.

Yeah, if your using non HDS units and have them networked via NMEA, than when you set a waypoint on any unit the cords will reflect the position of the shared puck.

  With the HDS units, each unit has an internal Antenna, so the waypoint you set would reflect the bow or console antenna.  You can select from the options menu to force one unit to use the other units GPS antenna, given you have them linked via hub or nmea.

Again I may be incorrect as I haven't really used my HDS units yet. Thats my general understanding at this point.

There in lies my problem understanding this.  Both units have their own antennas.  So you creat a waypoint and that unit uses its antenna and creates that point (obvious).

But when the point is shared to the other unit... does the second unit just use the recorded cordinates and find it using its own antenna?  If it dosn't then you are having to find it using the other antenna.

Mike, I realize there is inherant error in all GPS systems... but if I assume the wrong antenna it will still add, say 10 ft of extra error to my measurement.  I would have the normal 10-15 ft diameter of error and then 10 more feet of error from the bow to outside line of the first diameter.  I don't know..... surely they have thought of this and each unit uses its own position to go to that coordinate.

Only the cords are passed. The unit will find the waypoint using its own integrated antenna, unless you have specifically configured the unit to use the antenna in another networked head unit.

I did some reading online about these type of units from various companies.

The way I understand it, if you set the way point from the from front unit, then that means whatever unit you look it up on will lead you to that spot until that unit is located at that position.

So if you set it on the front unit, and then come back later using the rear unit, it will take you to that spot as of where the rear unit is, regardless of where the other unit is.

I did read where some newer units actually synchronize their locations so the unit gives you the option of "waypoint where front unit is", "waypoint where rear unit is", or "waypoint halfway between units".

When you are networked the position entered is the location of your LGC. Your recevier is actually in the LGC-2000, 300 or 4000, which ever one you have, not the display units. The waypoint will be saved in both units if you are using waypoint sharing.

If you are networked with an intergrated antenna then the display unit you choose to network off of will be the actual position displayed in both displays.

Guys, when you use an external antenna on a unit with an internal antenna the first thing you do is turn the internal antenna function off.

Why would you use an external antenna on a internal antenna unit?  My internals get better reception then my external did anyway.