Internal or external reciever

[powert]

Hi,

i was sifting through various sounder/gps combos and was curious to know what the advantages/disadvantages were of internal and external satellite receivers.

any advice would be appreciated

[TheRealAndy]

If you in an open boat (centre console) then you can use an internal antenna. If your in a half cab with a roof then you would use the external antenna.

The great thing about an external antenna is you place it where you get the best reception, and just remeber it does not take a lot of physical obstruction to kill the signal. I do a lot of hiking and I cant use a GPS in rain forest because of the tree canopy, its all map and compass for me.

[bigbrian47]

internal aerial is fine on a dash under a bimini etc
i've had one for a couple of years now with no problems
same in my 4b in the bush the only problem is overhead trees
have had a dash mounted lowrance in the 4b for 10 yrs no problems
except thick scrub
as TRA said a compass is an essential backup anyway both bush&water
cheers brian

[SatNav]

1. The decision depends on how much of a compromise you are prepared to accept

2. Depends on the actual mounting location relative to the user and other physical surroundings

3. External should always be the preferred option if available

4. There is no way to determine if an internal mount location will be ok as it is not the present signal that is important but the future signal.

5. The strength/quality of the signal today may not be the same when circumstances change

[dnej]

And as it was explained to me,why not get the external,because it can then be an either or situation,not being limited to where the antennae,can be mounted.
David

[BaitThrower]

Might also depend on brand of the GPS. I can get an accurate signal inside my house on an overcast day on the handheld Garmin GPSMAP 76CSx which has internal antenna. It takes alittle longer to acquire indoors thatn outdoors of course but it does get a signal and quite an accurate fix. Using it in rainforest with overhead canopy is no problem either. So might be worth asking around about brand and models too. Some are better than others!

[SatNav]

1. Getting a signal inside a house is dependant on many things including what the house is made off and other physical/environmental elements.

2. Accurate signal inside house? Based on what reference?

3. Overcast day? Will not affect GPS signals at all

4. Antenna's come in all shapes, sizes and class but even very sophisticated antenna's worth a few thousand dollars will not give an accurate position indoors

[Hamish73]

GPS signal inside a house? Are we talking about a greenhouse here ::)

But seriously, I have had a range of garmin handhelds, and as far as I know they all have the same 12 channel reciever, and none of them have ever worked inside our old weatherboard house. I do a lot of enduro riding through trees etc and generally GPS distance is about 90% of real distance, so it does a pretty good job of maintaining signal

[bluefin59]

I have a navman g.p.s with built in anntena and i can get a signal in a garage brick and tile with the garage door closed so i dont think a built in anntena is such a big problem ...matt

[SatNav]

1. Brick walls, tiled roof? Might be ok, Why don't you try a tin shed, tin roof and even leave the door open if you wish.

2. Boats don't always live in sheds do they?

[bluefin59]

No they dont mate ll i am saying is if i get a signal in there it wont be a problem on the dash of most boats ,i have taken mine out in a 6m hard top trailcraft and it worked fine....matt

[SatNav]

1. The point I am trying to get accross is that just because it works today does not mean it will work tomorrow as GPS service is not totally predictable and should not be expected either.

2. Because you get a signal only indicates that at particular point in time you are getting a signal, it does not indicate future possibilities.

[seatime]

1. The point I am trying to get accross is that just because it works today does not mean it will work tomorrow as GPS service is not totally predictable and should not be expected either.

2. Because you get a signal only indicates that at particular point in time you are getting a signal, it does not indicate future possibilities.


Can you can add to that, inside a structure on land the aerial (internal or external) isn't moving about as the unit/aerial will often do when on the water.

[Xtreme]

Powert,

I'm with SatNav, internal aerials are an easy option but thats where the benefits stop. In my practical experience with Lowrance units, the internal aerial units take longer to lock on satellites and hold fewer locks. They'll still work mind you but they are not an equivalent IMHO.

[joeT]

Units with an inbuilt antenna usually can't be flush mounted.

[BaitThrower]

1. Brick walls, tiled roof? Might be ok, Why don't you try a tin shed, tin roof and even leave the door open if you wish.



I get a signal just fine in a 2-story brick and tile. Out of interest just tried it in my tin shed out the back. Yep got a signal. Accuracy not as good as inside the house but still got a signal that would give me a rough position within 20m. Me thinks some handhelds are better than others :o

[SatNav]

1. GPS users need to loose this notion that GPS works fine in buildings as they simply do not provide an acceptable order of service

2. This is a very misleading concept

[BaitThrower]

1. GPS users need to loose this notion that GPS works fine in buildings as they simply do not provide an acceptable order of service

2. This is a very misleading concept

Why loose it when it is true?
I have street maps installed on my GPS and when inside, it is showing me pretty much where I am at the current street location...

Of course there is little reason to be using a GPS indoors anyway really, but I don't see why we need to loose any notion at all when the evidence is right there staring you in the face? Have you used one of the better handhelds like the Garmin 76CSx? Mate it works indoors, in rain forests under heavy canopy, even in my tin shed (although not as well). It's a bloody good unit!

Note also that the 76CSx is WAAS compatible which further improves its accuracy and availability. WAAS is generally only available in the USA but according to some WAAS graphics, there is potential availability close to the eastern seaboard of Australia...

From wikipedia:
The WAAS specification requires it to provide a position accuracy of 7.6 meters or better (for both lateral and vertical measurements), at least 95% of the time. Actual performance measurements of system at specific locations have shown it typically provides better than 1.0 meters laterally and 1.5 meters vertically throughout most of the contiguous United States (http://en.wikipedia.org/wiki/Contiguous_United_States) and large parts of Canada (http://en.wikipedia.org/wiki/Canada) and Alaska (http://en.wikipedia.org/wiki/Alaska).[2] (http://en.wikipedia.org/wiki/Wide_Area_Augmentation_System#_note-WAAS_NSTB_PAN_Report_Jul06) With these results, WAAS is capable of achieving the required Category I precision approach accuracy of 16 m laterally and 4.0 m vertically.

http://en.wikipedia.org/wiki/Wide_Area_Augmentation_System

[SatNav]

1. If the evidence was there then they would have solved the mobile phone issues with 911/000 type calls a long time ago.

2. There is a good reason why this has not happenned but obviously some continue to not understand the issue behind not currently being able to use GPS for this purpose.

[BaitThrower]

aren't we talking about GPS and internal/external antennas? All I'm saying is my internal antenna Garmin GPS works indoors, probably due to the fact that it may be working better using the WAAS as I mentioned above... and perhaps the SIRF technology it uses too?

The fact remains, my GPS works fine indoors and that is my reply to earlier posts. Obviously, not ALL GPS receivers do, so its an exception to the "rule", which obviously is not a solid one anyway :)

[SatNav]

"Can you can add to that, inside a structure on land the aerial (internal or external) isn't moving about as the unit/aerial will often do when on the water."

1. The moving about bit is the key as heading in different directions will create a different set of circumstances depending on where the GPs is mounted

2. Satellites also move and at different times of the day satellite numbers can be quite low creating poor signal, reception and position quality

[BaitThrower]

fair enough but I've never had any problem outdoors or using it on the boat so far. It has always retained a good fix with at least half a dozen satellites outdoors.

[SatNav]

"All I'm saying is my internal antenna Garmin GPS works indoors, probably due to the fact that it may be working better using the WAAS as I mentioned above..."

1. The first thing you need to do is turn WAAS off as it simply does not work in Australia

2. Then how about you convince me your simplistic el cheapo patch type antenna can out perform some of the high end geodetic antenna's then I want to see the evidence not a perception

3. Not even high end antenna's work fine indoors

[BaitThrower]

According to this CASA article, Australia can get U.S. WAAS signals from the INMARSAT Pacific satellite?
http://www.casa.gov.au/fsa/2005/aug/54-55.pdf

[BaitThrower]

"All I'm saying is my internal antenna Garmin GPS works indoors, probably due to the fact that it may be working better using the WAAS as I mentioned above..."

1. The first thing you need to do is turn WAAS off as it simply does not work in Australia

2. Then how about you convince me your simplistic el cheapo patch type antenna can out perform some of the high end geodetic antenna's then I want to see the evidence not a perception

3. Not even high end antenna's work fine indoors

I'm not saying this internal antenna can outperform high end antennas. But if it works inside, and they don,t well maybe it can, reception wise at least. The fact is that here I am sitting inside, moving or not moving and I am still getting a fairly accurate fix on my location, well within 20m I would say according to my map. Do I need to take a photo to prove it??

[FNQCairns]

I remember the episode where the Goodies (some young blokes will not know who I am talking about) were driving their house down the highway, possibly an application for this GPS:).
My Garmin 12 works also indoors too, of coarse until my indoors move consistantly I will have no need to fit an external aerial.
My Garmin 12 can make tracks well enough to overlay on a map from under the car seat!!

Some seem to recieve far better than others I have used, at least in my experience.

cheers fnq

[SatNav]

1. POR (inmar3f3) no longer carries a WAAS signal

2. The nearest WAAS satellite now is AOR-W which even from the east coast is quite low on the horizon

3. There is not and never have been any ground station in Australia for WAAS to determine corrections from.

4. Enabling WAAS in Australia will generally degrade accuracy not improve it.

5. AirServices Australia have developed what is in fact a much better and cheaper solution to WAAS due to the fact that WAAS does not work in Australia

6. AirServices have called their system GRAS and currently even selling the technology back into the US where WAAS doesn't actually work to spec either

[BaitThrower]

1. POR (inmar3f3) no longer carries a WAAS signal

2. The nearest WAAS satellite now is AOR-W which even from the east coast is quite low on the horizon

3. There is not and never have been any ground station in Australia for WAAS to determine corrections from.

4. Enabling WAAS in Australia will generally degrade accuracy not improve it.

5. AirServices Australia have developed what is in fact a much better and cheaper solution to WAAS due to the fact that WAAS does not work in Australia

6. AirServices have called their system GRAS and currently even selling the technology back into the US where WAAS doesn't actually work to spec either

Ok, WAAS or no WAAS, it still work indoors for me :) I just disabled WAAS and I still have signal.

[SatNav]

1. Disabling WAAS won't change the GPS signal but will most likely change the accuracy for the better.

2. Now you might actally be in real world coordinates?

3. Wonder how many other GPS users outside of the US have WAAS enabled and Why?

[FNQCairns]

1. Disabling WAAS won't change the GPS signal but will most likely change the accuracy for the better.

2. Now you might actally be in real world coordinates?

3. Wonder how many other GPS users outside of the US have WAAS enabled and Why?

Will have to check my chart plotter just in case!

cheers fnq

[Local_Guy]

From my experiences external GPS on sounders locates a fix almost instantly, where as internal can take up to 5mins but holds it once aquired.
The sounders i'm comparing is Humminbird 727 with external and Lowrance LMS-527 iGPS.

Both of my units were mounted in basically teh same spot.. behind the centre console window so they both had the same obstruction (controled conditions if you want to call it that).

I went Internal receiver on my new GPS so i would have extra room for other units later on.

Look at your needs and where your unit is going to go. both have their advantages and disadvantages.

[uripper]

Because the internal antennas are mounted in the top of the units they won't receive if anything thicker than a bimini canvas is above them. The external's eliminate this problem so if you have to go through timber or a f'glass cabin put a mushroom antenna on.

as for receiving in a brick house I highly doubt it except if its anything like a E series Raymarine.......

[TheRealAndy]

Well I purchased a Lowrance LMS-527 on the weekend with an internal antenna. I installed it in the garage of my brick and tile house and it locked onto some satellites (must be at least 3) and gave me a position. Infact, it event set up the time and units of measure based on my location!

Its worth noting that one of the big selling points for the hikers is the newish SiRFstar III chipsets. Apparently these chipsets can lock onto satellites even under dense tree canopies. I notice that this is not a marketing point of MArine GPS', probably due to the fact that physical obstructions are pretty unlikely on the water. Nevertheless, it would expain as to why people are able to lock onto satellites whilst in the garage.

When I figure the new sounder out I will post how many satellites it has locked onto whilst sitting in the garage.

[TheRealAndy]

Interestingly enough, I could not get a fix whilst it was raining. Still in the garage, i got a fix about 20minutes later. 8 satellites. Whilst it was raining I got 2 satellites no problem, would get the magical number 3 but not long enough to get a fix.

Now I need to figure out how to get that navionics map to work..

[trueblue]

I went with the external unit, and mounted that on the dash with the extra cable just coiled up out of the way. That gives me the opportunity of using the same GPS on any upgraded boat I might get where an internal unit won't work.

cheers

Mick

[SatNav]

1. The rain scenario on a roof is close as typically weather/rain does not affect GPS signals BUT rain on a roof is no longer rain but is a film of water and that is something quite different.

2. Similar with the majority of trees, dry fine, when wet/dew etc become a total brick wall. Stand out in the rain no problem.

3. One other thing that is helping with signal reception these days is the number of satellites. As of last saturday's GPS launch the system will now have for the first time a full house, no more vacancies.

[TheRealAndy]

Actually, heavy rain does affect satellite reception. Ask any foxtel subscriber that gets there signal from a satellite. My dish is outside, and I still loose reception in heavy rain.

[bluefin59]

Because the internal antennas are mounted in the top of the units they won't receive if anything thicker than a bimini canvas is above them. The external's eliminate this problem so if you have to go through timber or a f'glass cabin put a mushroom antenna on.

as for receiving in a brick house I highly doubt it except if its anything like a E series Raymarine.......

What a load of garbage i can back up my statement as to it working fine in a cabin with a hardtop and glass windows so you are wrong there as i have done it more than once and it does work in a house also and mines a crappy navman ...matt

[SatNav]

1. Please lets not confuse and compare the signals between Foxtel and GPS satellites, the only similarity is they are both satellite based, nothing more.

2. Totally totally totally different comparison

[TheRealAndy]

Well the other similarity is they are both radio signals and are both microwave frequencies.

[Wahoo]

some good reading satnav, thanks

Daz