Topic: GPS Position Establishment and Quality - Internal vs. External

[jimmybass2]

I have 2 HB Units on my boat. The helm has a 798C SI with the external AS-GR50 puck. The bow has a 788Ci with the internal antenna.

Here are the differences that concern me:

798 External gets a fix in a matter of 5-10 seconds and gets claimed accuracy within 0-6 feet, with an Enhanced Fix and a bunch of Satelites.

788 Internal takes at least a full minute to get a fix and gets claimed accuracy in the 30 foot range, with an 3D Fix and far fewer Satelites.

I'm told, by HB Tech Support, that both units are 50 channel.

So, the questions are:
Is this normal?
Is the 788 a 50 Channel?
Is the signal quality of the External AS-GR50 that much better than the Internal Antenna?
Will I get 788 signal improvement if I add a AS-GR50 receiver?
If so, how do I tell the 788 to use the new puck? (When I set the 788 to External now, it uses the AS-GR50 connected to the 798, via my InterLink).

MY GOAL is improved Accuracy in the signal and location for the 788 on the bow. I don't want to be 30+ feet away from my waypoints when in deep water!

Thanks in advance for the help!

Jimmy

[RGecy]

I am going to forward this on to Greg and see if he has time to answer your question acurately.  He has been busy at work lately and hasn't been on the forums very much. 

My guess is that the 788's originally shipped with the GR16 and was later upgrade to the GR50. 

What is the serial number on your unit and when did you purchase it?

Robert

[majflyboy]

Robert, can you give us the before and after serial numbers for the 788 ducer changeover?  Thanks

[jimmybass2]

Robert,
Thanks for your help!!!   

Serial #: 9091803-0111.  Purchased 12/23/2009.

Jimmy

[Humminbird_Greg]

Guys, I’m pretty sure that all of the 788ci units shipped with the same 50 channel internal GPS Receiver that we still use now.  While there are differences between the internal and external GPS Receivers they should be pretty close to one another in the accuracy department.  I have never heard of them being that far off.  Basically the internal GPS Receiver is the external GPS Receiver minus some ground shielding (this helps reduce interference and allows for a higher signal-to-noise ratio so it can lock on those weaker satellite signals which may allow for a more accurate position fix).

When you set the 788ci to use the external GPS Receiver from the 798, what does it show for the Estimated Position Accuracy?

Is there something that could be blocking any of the satellite signals from getting to the 788ci unit (and therefore the internal GPS Receiver)?  If both GPS Receivers have the same unblocked view of the satellites than both should be showing the same satellites and about the same estimated position accuracy.

Are both units running the latest version of software?

Does this happen with all other devices and motors on the boat turned off?


To answer your questions:
1.) Is this normal?
No.

2.) Is the 788 a 50 Channel?
Yes

3.) Is the signal quality of the External AS-GR50 that much better than the Internal Antenna?
No it is not that much better.  The external GPS Receiver should be a little better but it is normally only better is a high noise environment.

4.) Will I get 788 signal improvement if I add a AS-GR50 receiver?
Possibly but a noticeable gain in signal improvement may be due to external noise or a better GPS Receiver position.  There could also be something wrong with the internal GPS Receiver in the 788ci unit.

5.) If so, how do I tell the 788 to use the new puck? (When I set the 788 to External now, it uses the AS-GR50 connected to the 798, via my InterLink).
You will do this just like when you switched to the “Remote External GPS” setting to use the external GPS Receiver of the 798 unit.  You would use the same GPS Override menu but select the “External GPS” setting instead.

I hope that answers your questions Jimmy.


Thanks for the ‘heads-up’ on this Robert. Maybe things will slow down a little bit more for me at work and home – I sure miss helping out everyone!

[jimmybass2]

Greg and Robert,
Thanks for the help!!!

As usual, the advise given here was right on.  My differences in connection quality was based on the boat being backed into the garage.  The Puck performs much better in the garage than the internal unit.  Out on the lake today, both the internal and external had enhanced position and accuracy from 0 to 5 feet.  The fact that the boat was in/near the garage was the problem.

Thanks again!!!!
Jimmy