I just received my new Garmin Map76s. I haven't had it on the boat yet. I
took it to the beach yesterday (Oregon coast) and pointed it to the south
west, slightly elevated. After a few minutes, it found satellite 47, and
after a few minutes more it indicated differential GPS. It didn't take very
long in the car traveling home before it lost the differential indication.
My question is: After mounting the bracket on my boat, will I only get
differential GPS when traveling SW, and would an external antenna be the
cure? Thanks.

On the west coast, the WAAS birds are only about 15 degrees above
the horizon, so it's really easy to loose them on land. The good news
is that they stay locked up well on the ocean, at least in the Monterey
area. As long as your GPS has a clear view to the southwest, it
should work fine.

Travel direction isn't relevant, except as it might make part of the
boat hide the bird.

--
Chuck Tribolet

http://www.almaden.ibm.com/cs/people/triblet

Silicon Valley: STILL the best day job in the world.


"Steve Alexanderson" Idon'tlikegreeneggsandspamIdon'tlikethemsamIamsal wrote in message
...
I just received my new Garmin Map76s. I haven't had it on the boat yet. I
took it to the beach yesterday (Oregon coast) and pointed it to the south
west, slightly elevated. After a few minutes, it found satellite 47, and
after a few minutes more it indicated differential GPS. It didn't take very
long in the car traveling home before it lost the differential indication.
My question is: After mounting the bracket on my boat, will I only get
differential GPS when traveling SW, and would an external antenna be the
cure? Thanks.

The internal antenna is clearly directional, as signal strength varies
greatly as it is moved about. That's why I wondered if travel direction (or
mounting angle) was important when in a fixed mount. Maybe once it locks on,
though, a lower signal strength will keep WAAS active?? Guess I'll know
better once I have it in the boat.

"Chuck Tribolet" wrote in message
...
On the west coast, the WAAS birds are only about 15 degrees above
the horizon, so it's really easy to loose them on land. The good news
is that they stay locked up well on the ocean, at least in the Monterey
area. As long as your GPS has a clear view to the southwest, it
should work fine.

Travel direction isn't relevant, except as it might make part of the
boat hide the bird.

--
Chuck Tribolet

http://www.almaden.ibm.com/cs/people/triblet

Silicon Valley: STILL the best day job in the world.


"Steve Alexanderson"
Idon'tlikegreeneggsandspamIdon'tlikethemsamIamsal
wrote in message
...
I just received my new Garmin Map76s. I haven't had it on the boat yet.
I
took it to the beach yesterday (Oregon coast) and pointed it to the
south
west, slightly elevated. After a few minutes, it found satellite 47, and
after a few minutes more it indicated differential GPS. It didn't take
very
long in the car traveling home before it lost the differential
indication.
My question is: After mounting the bracket on my boat, will I only get
differential GPS when traveling SW, and would an external antenna be the
cure? Thanks.

On Fri, 16 Jan 2004 15:59:48 -0800, "Chuck Tribolet"
wrote:

On the west coast, the WAAS birds are only about 15 degrees above
the horizon, so it's really easy to loose them on land. The good news
is that they stay locked up well on the ocean, at least in the Monterey
area. As long as your GPS has a clear view to the southwest, it
should work fine.

Travel direction isn't relevant, except as it might make part of the
boat hide the bird.

You learn something new everyday - I didn't know that.

Interesting - thanks.

Later,

Tom
S. Woodstock, CT
----------
"My rod and my reel - they comfort me."

St. Pete, 12 Lb. Test

To find the angle of the geostationary WAAS satellites from your area,
go to:
http://www.directv.com/DTVAPP/DishPointerAction.do
at Direct TV and put your zip code into the box on the page. DTV will
tell you how to set the elevation on your DTV dish and that angle is
the angle the WAAS birds are from your latitude. All geostationary
satellites occupy the same 22,800 mile band around the equator.

For Charleston, SC, the data comes back:

For your zip Code 29418 the azimuth and elevation are displayed below:


DIRECTV Dish Pointer

Azimuth 220.9

Elevation 45.6

The Azimuth is irrelevant to WAAS birds. The elevation above the
horizon is the same. This is also the elevation if you have a 137 Mhz
GOES weather satellite receiver or any other geostationary satellite
use. The higher, the better, of course. The direct satellite radios
like XM and Sirius work better in the South, too...(c;



Larry W4CSC

On Sat, 17 Jan 2004 15:02:40 GMT, (Larry W4CSC) wrote:

To find the angle of the geostationary WAAS satellites from your area,
go to:
http://www.directv.com/DTVAPP/DishPointerAction.do
at Direct TV and put your zip code into the box on the page. DTV will
tell you how to set the elevation on your DTV dish and that angle is
the angle the WAAS birds are from your latitude. All geostationary
satellites occupy the same 22,800 mile band around the equator.

For Charleston, SC, the data comes back:

For your zip Code 29418 the azimuth and elevation are displayed below:


DIRECTV Dish Pointer

Azimuth 220.9

Elevation 45.6

The Azimuth is irrelevant to WAAS birds. The elevation above the
horizon is the same. This is also the elevation if you have a 137 Mhz
GOES weather satellite receiver or any other geostationary satellite
use. The higher, the better, of course. The direct satellite radios
like XM and Sirius work better in the South, too...(c;

Now that's two new things I learned today.

I keep this up, I might get smart or something.

Later,

Tom
S. Woodstock, CT
----------
"My rod and my reel - they comfort me."

St. Pete, 12 Lb. Test

On Sat, 17 Jan 2004 19:59:00 GMT, Short Wave Sportfishing
wrote:


Now that's two new things I learned today.

I keep this up, I might get smart or something.

Later,

Tom
S. Woodstock, CT

We're holding Captain's Mast on the main deck later on this afternoon.
Many sailors learn all kinds of new things, every time we hold it....

Keel hauling will be first thing in the morning, tomorrow. THIS time
we're going to try it WITHOUT the engine running, too! Last time was
a little 'messy' and the sharks followed us for a week!



Larry W4CSC

Larry, this is one of the rare occasions when you are wrong. Different
geostationary birds will have different elevations. The one straight
south of you will have an elevation of about 90 minus latitude degrees
and will be the highest. One 180 degrees around the world will
have a negative elevation.

--
Chuck Tribolet

http://www.almaden.ibm.com/cs/people/triblet

Silicon Valley: STILL the best day job in the world.


"Larry W4CSC" wrote in message ...
To find the angle of the geostationary WAAS satellites from your area,
go to:
http://www.directv.com/DTVAPP/DishPointerAction.do
at Direct TV and put your zip code into the box on the page. DTV will
tell you how to set the elevation on your DTV dish and that angle is
the angle the WAAS birds are from your latitude. All geostationary
satellites occupy the same 22,800 mile band around the equator.

For Charleston, SC, the data comes back:

For your zip Code 29418 the azimuth and elevation are displayed below:


DIRECTV Dish Pointer

Azimuth 220.9

Elevation 45.6

The Azimuth is irrelevant to WAAS birds. The elevation above the
horizon is the same. This is also the elevation if you have a 137 Mhz
GOES weather satellite receiver or any other geostationary satellite
use. The higher, the better, of course. The direct satellite radios
like XM and Sirius work better in the South, too...(c;



Larry W4CSC

On Sat, 17 Jan 2004 19:35:20 -0800, "Chuck Tribolet"
wrote:

Larry, this is one of the rare occasions when you are wrong. Different
geostationary birds will have different elevations. The one straight
south of you will have an elevation of about 90 minus latitude degrees
and will be the highest. One 180 degrees around the world will
have a negative elevation.

--
Chuck Tribolet

http://www.almaden.ibm.com/cs/people/triblet

You are correctimundo, however as the GPS antenna is not pointable,
the website will give them a fair idea, within a few degrees, of the
elevation of any geostationary bird from their zip code. The further
north you go the worse the problem. The website won't tell them
EXACTLY how bad it is, but will give them a general idea.....

Hmm.....we could take one of these gyro stabilized DirecTV dishes,
replace the 10 Ghz feedhorn with a WAAS feed horn.....Nope, we're
gonna need a bigger dish to make it have more gain.....(c;

HEY, my neighbor has one of those REALLY BIG old satellite antennas
that's scrambled now he's not using!........hee hee.

On a more serious note, I don't believe the GPS has to have CONSTANT
WAAS data to make it accurate. The drift you get corrected for is
VERY slow moving, so if it had a lock on WAAS data every few minutes
that should be good enough for good correction, shouldn't it? I'd
think the manufacturers would tell the receiver to use the LAST
available data until new data arrives.



Larry W4CSC

On the west coast, the WAAS birds are only about 15 degrees above
the horizon . . .

If the DirecTV test below is accurate, it's 33.4 degrees @ Portland,
still quite blockable in terrain and urban canyons.