GPS Internal or External antenna???

skytracker

Seaman Apprentice
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Apr 11, 2008
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Hi guys, I'm a long time reader and only recently started posting. This is just a great forum.
What are your opinions on the internal GPS antennas in the combo units.
I have had both and I can see being able to put it in a vehicle or temporarily in another boat is one. Do you guys think mounting a unit on the console near the windshield might knock the signal down too much or not?? I have one with the external on another boat and it works great of course but I am thinking of the Lowrance 522c with the internal for my fish and ski boat. All of your experience and opinions are welcome, Thanks.
 

tommays

Admiral
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Jul 4, 2004
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Re: GPS Internal or External antenna???

The new units are so much more better with weak singles that i have not had a problem


On small boats 19 to 20 foot it can be hard to place and external Ant were it will not get damaged and there really expensive ,a Lowrance replacement Ant is about 250 dollars :eek:
 

skytracker

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Re: GPS Internal or External antenna???

Thanks Tommays,
I think I am going to try the 522 with the internal and see how I like it.
I've used my portable Garmin on a RAM mount before on it. Occasionally it lost signal but for the most part was good. The fact about replacement antennas is a good point. Any suggestions are welcome.
 

bruceb58

Supreme Mariner
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Re: GPS Internal or External antenna???

If you want to put a fuel sensor on the NEMA 2000 bus and have the unit calculate MPG then you need the external antenna. If that doesn't matter to you, I would get the internal.
 

JB

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Re: GPS Internal or External antenna???

I have mounted Garmin GPS38, GPS12MAP, GPSMAP 162 and GPSMAP 276C on the dash and all worked just fine with the internal antennae.
 

Boatist

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Re: GPS Internal or External antenna???

If your out on the open water and mount your unit up near the window with glass all around the internal will work just fine.

The unit will pick up the normal GPS Satellites with no problem. If you have any problem it would be with the WAAS Satellites that are use to correct error and make your postion more accurate. With out the WAAS Birds your accurate to about 30 feet and with the WAAS birds good to about 10 feet. These Satellites are over the Equator and in GeoStationary orbits so they are 38400 miles up. If your way up north then these sattelites will be low on the horizon. I have not had any problems picking up since they repostioned a couple of years back but them I am only 38 degrees North.

If your way up North and 10 foot accuracy is important to you them the unit or the antenna need to be mounted where it will have a clear view to the south and Low on the southern horizon this would be eaiser with the external antenna.
 

Tacklewasher

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Re: GPS Internal or External antenna???

The 522 will take an external antenna if you like. Not sure the cost but it is an option.

Mine is brand new in the box, just picked it up today. I plan to use it in multiple boats, either fixed in my 18 foot or with a portable setup for my smaller boats so I went with the internal. My 18 foot also has a soft top so I am sure it will work fine there.

Also, I think bruceb58 is incorrect as the manual I just started reading shows how to connect the fuel meter or anything else to the NMEA 2000 on the 522.
 

bruceb58

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Re: GPS Internal or External antenna???

You can hook up the fuel sensor, it just won't allow the calculation of MPG with an internal antenna. I know that sounds weird but I verified this with Lowrance. I returned an internal antenna version for this reason.
 

burp

Petty Officer 1st Class
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Messages
363
Re: GPS Internal or External antenna???

My Garmin 182C with an internal antenna works fine mounted beneath the windshield and bimini......How many cars have you passed with the GPS stuck to the windshield? They all seem to work fine too.
 

dingbat

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Re: GPS Internal or External antenna???

......How many cars have you passed with the GPS stuck to the windshield? They all seem to work fine too.

It all depends on your needs and expectations. How accurate do you need to be to make a right turn at an intersection? How about finding a needle in a hay stack?

If you want your unit to "work fine" install it using the internal antenna. If you want the unit to perform at its best go with an external antenna.
 

bruceb58

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Re: GPS Internal or External antenna???

If you want your unit to "work fine" install it using the internal antenna. If you want the unit to perform at its best go with an external antenna.

You apparently don't understand how a GPS works. You can half the signal strength with one antenna position and still have the same accuracy compared to another higher signal strength antenna location. As long as the signal strength is high enough to correlate the digital stream being sent from the satellite, it doesn't matter if the signal is higher. You gain no more accuracy. It is true that you may see more satellites and the GPS unit has more to choose from but in a boating environment, most satellites are visible because there are less mountains and trees vs a land environment.
 

dingbat

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Re: GPS Internal or External antenna???

I have two GPS units on board sitting side by side. One is a Garmin 4208 with the antenna mounted on top of the hard top. The back up unit is a Garmin 162 with the internal antenna.

The DOP and EPE is consistently better, sometimes by a factor of 2, on the 4208 than the 162. Either there is a large disparity in the way the two units calculate position using the available data or the remote antenna?s ability to pull in the additional birds (12 vs. 4-6) is creating the dramatic increase in accuracy.

Either way this is a real world side by side comparison of two units operating under the exact same conditions. One with and one without a remote antenna.
 

skytracker

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Re: GPS Internal or External antenna???

Thanks for all the information guys. The reason i was thinking of going internal was similar to Tacklewasher, being able to use it on multiple boats without addditional antennas. I am very familiar with GPS systems, and every additional satellite the unit sees increases the accuracy. So the external is likely to be more accurate depending on the antenna position and coax length to the antenna.
 

jennis9

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Mar 22, 2008
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Re: GPS Internal or External antenna???

We bought the 322c at the end of the season last year and got it for a steal. went with the external antennae, the expert at the store said we'd find better performance with the external and the MPG comment is also correct.

we're having trouble getting the GPS to work at this point (fishfinder works great) the length of the cord for the antennae is not that long - so we had to mount it on the gunnal under the support for the windshield - this may be one problem. we get "GPS not responding," I'll let you know what our findings are in case it's our mounting location.
 

bruceb58

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Re: GPS Internal or External antenna???

we're having trouble getting the GPS to work at this point (fishfinder works great) the length of the cord for the antennae is not that long - so we had to mount it on the gunnal under the support for the windshield - this may be one problem. we get "GPS not responding," I'll let you know what our findings are in case it's our mounting location.

The "GPS not responding" is a Lowrance NEMA interface problem. I get that too with my Lowrance unit. Repowering the GPS puck resets the interface and all is good after that. Could also be a network termination issue.
 

bruceb58

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Re: GPS Internal or External antenna???

The DOP and EPE is consistently better, sometimes by a factor of 2, on the 4208 than the 162. Either there is a large disparity in the way the two units calculate position using the available data or the remote antenna’s ability to pull in the additional birds (12 vs. 4-6) is creating the dramatic increase in accuracy.

So what is the difference in accuracy between the two units? Are we talking maybe 20 feet?

The EPE is actually derived off of the DOP so they are pretty much one in the same. The DOP is calculated using the geometry of the satellites...basically picking satellites that give the best triangulation so as to produce the least amount of error. Comparing two different models of GPS will give you two different DOP values because each units software may use different algorithms to pick the best satellites to use for the calculations. to determine if it as antenna issue, you really need the same model GPS with two different types of antennas.

For marine use, the accuracy you get will almost always be satisfactory for the average boater.
 

dingbat

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Re: GPS Internal or External antenna???

I?m no GPS expert so please bear with me. I'm more of a radiation, mass absorption type guy:D

If the quantity and quality of the reception doesn't have a bearing on accuracy then why 12 or even 16 channels as Lowrance is now boosting? You only need 3 to make a triangulation calculation? Why give SNR readings for each channel?

Logic would tell me that the greater the sampling capability the greater the sigma of the positioning accuracy.

To answer your earlier question, it?s typically much less than 20?. Typically more like 8-10? I would guess. 8-10' may not be a lot but when you?re looking at a DOP of 3.6? that 8? is statically huge.
 

jennis9

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Re: GPS Internal or External antenna???

thanks bruceb58 - didn't want this post to get sidetracked.
 

bruceb58

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Re: GPS Internal or External antenna???

Actually need 4 satellites to do a complete fix if you want elevation data. It is true that the more satellites that the GPS sees, the more averaging can be done between the data received from all of the satellites. There is error produced by the signals going through the ionosphere(among other effects) that changes the delay calculated. It is a combination of the delay error and the angle of the satellite relative to the receiver that determines the positioning error, not the SNR that the receiver sees for the satellite signal.

I am not a GPS expert either...just an electrical engineer that took a GPS Navstar class back when I did my masters and did missile guidance work incorprating GPS receivers.
 

tommays

Admiral
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Re: GPS Internal or External antenna???

Well

I think my current Lowrance Ext unit is more accurate than my 1995 magellan pioneer (GPS 330) just because of inprovement in the tech used

600 dollars VS 99 dollars

BUT i cant say eather has gotten me lost :D
 
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