HDS 8 Question

[410shooter]

Why does my HDS 8 need to be reset each time I go to a new lake, position wise? Am I not waiting long enough for it to find itself. My new position is about 40 miles from my old position. I have been doing a reboot to factory settings and all is well, what's up?

[Three Rivers Marine]

Originally Posted by 410shooter

Why does my HDS 8 need to be reset each time I go to a new lake, position wise? Am I not waiting long enough for it to find itself. My new position is about 40 miles from my old position. I have been doing a reboot to factory settings and all is well, what's up?

HDS units when they first fire up are reading from their last known position. When you first turn it on at a different position that is quite a ways from your last position, give it a few minutes to lock on and show where you're at. Do you you have your unit hooked up to an external antenna, or are you using the one in the unit?

Keith

[jhebert]

A GPS receiver needs to have a very good idea of the time and date, and a rough idea of its location to work effectively. I doubt very much that a change in location of a few miles between lakes is going to confuse a GPS receiver. If you moved the receiver 1,000-miles between uses, it might be a bit confused.

A GPS receiver does not "find itself"--it needs to find satellites in the sky. A GPS receiver listens for the signals from space from the GPS satellites it expects ought to be in view. The GPS receiver typically keeps in memory an ephemeris, that is, a table of the satellites in orbit. Based on the time and location, it presumes that certain satellites will be in view. It looks for those satellites first. If the time keeping of the GPS is way off, or of you move it a very long distance between uses, when it is restarted it may not be looking for the proper satellites.

If the GPS receiver is not seeded with the proper satellites to hunt for, it may take it a while to find the first satellite. There are about 30 satellites in orbit. If the GPS receiver is not informed about which ones ought to be in view it could be a while before it works its way through all the options and finds the first one.

Once the GPS receiver acquires three satellites it can work out a two-dimension position fix. In a modern GPS receiver this usually happens in less than a minute. If the GPS receiver does not have a good view of the sky, it may only be able to acquire satellites that are in certain portions of the sky. This reduces the chances of getting three satellites acquired. If the GPS receiver is being interfered with by some local signals, its sensitivity may be decreased, and it may have trouble acquiring satellites at low elevations as those signals are weaker than ones from satellites higher overhead.

The GPS receiver in the HDS is quite good. I have never had to apply any sort of restart or reset to the device to allow the GPS receiver to deduce its position. If I use it indoors and the satellites in view are all at low elevations, it can take a few minutes to deduce a position fix.

[410shooter]

I guess I will wait longer the next time for it to aquire satellites. Just seems like I did wait and all it showed was last position. I am not getting any failure messages. No external antenna just the internal one.

[jhebert]

Originally Posted by 410shooter

I guess I will wait longer the next time for it to aquire satellites. Just seems like I did wait and all it showed was last position. I am not getting any failure messages. No external antenna just the internal one.

The GPS should never show a position fix from sometime previous. It either has a position fix for this instant or did does not have a position fix. It never shows an out-of-date position as a current position fix. Maybe you are confusing yourself by having the CHART in the mode where it shows the position of the cursor, not the vessel.

[doubleheader]

Seems to me this happened to me with my HDS8, and I just hit exit and it found the location.