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Satellites


hookedoncache
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So how many satellites do you normally see in you GPSr and where are you located?

 

I ask not because I'm new but it might help others to understand what to expect! Here in the Charlotte, NC area I usually see 4 to 6 and that seems a low number to me after reading for the last 2 hours the past threads around this topic.

 

Maybe it would be a little more helpful if we include our GPSr model and conditions!

 

4-8 satellites

clear sky closer to 8

in the woods 1 to 4 with signal loss hence the 1...

Charlotte, NC

Garmin 60CS

 

Others? ;)

Edited by mlail
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So how many satellites do you normally see in you GPSr and where are you located?

 

I ask not because I'm new but it might help others to understand what to expect! Here in the Charlotte, NC area I usually see 4 to 6 and that seems a low number to me after reading for the last 2 hours the past threads around this topic.

 

Maybe it would be a little more helpful if we include our GPSr model and conditions!

 

4-8 satellites

clear sky closer to 8

in the woods 1 to 4 with signal loss hence the 1...

Charlotte, NC

Garmin 60CS

 

Others? :rolleyes:

It's not going to help you much. The SVs are not geosynchronous, but are in constant motion in relation to your position. The SV configuration now will be different than in an hour.

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you need a minimum of 3 for position - four for 3D (Altitude)

 

after that it increases the accuracy

 

WAAS requires getting one of the 2 geosynchronous birds

 

These are the absolute min's -

 

neither my magellan nor the Etrex will show position on 2 birds - the instructions say about the same for the Magellan.

 

wide open areas, tops of hills, and higher altitudes increase the ability to get more birds.

 

low areas - trees! - hills - urban jungles (tall buildings) all block signals and chance for wider spread of birds.

 

hope that helps -

Edited by CompuCash
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So how many satellites do you normally see in you GPSr and where are you located?

If I recall correctly, on my Garmin 12 and eTrex Legend- it can display up to 12 birds on each. The G12 usually under clear sky conditiond will actually lock on to 6-8 birds. The legend in WAAS - I believe locked to 3 birds, in reg. mode - I think it locked into 5 birds the last time out. Location is Buffalo NY. SF1

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I thought you needed 4, at least for the initial lock, as the fourth satellite is used to correct timing differences between the satellites' very accurate cesium clocks, and your GPSr's not quite so accurate clock. The method by which this is done is ingenious, and without it, GPSrs would probably not exist.

 

It wasn't for the time discrepancy, only three would ever be needed for 3D, I think.

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It wasn't for the time discrepancy, only three would ever be needed for 3D, I think.

Thanks for the explanationn. I always wondered why it wanted four, since three should theoretically be enough.

 

And I often have a hard time getting and keeping 4, caching a lot of wooded areas in New England. Though I find getting and keeping the requisite number in a big city even harder.

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I thought you needed 4, at least for the initial lock, as the fourth satellite is used to correct timing differences between the satellites' very accurate cesium clocks, and your GPSr's not quite so accurate clock. The method by which this is done is ingenious, and without it, GPSrs would probably not exist.

 

It wasn't for the time discrepancy, only three would ever be needed for 3D, I think.

It only takes 3 to get a lock. A 3 SV lock actually defines 2 points, one on (or near) the earth's surface, and one in space. The GPSr assumes that you haven't left the planet, and ignores the other point.

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you need a minimum of 3 for position -

four for 3D (Altitude)

 

after that it increases the accuracy

 

WAAS requires getting one of the 2 geosynchronous birds

 

These are the absolute min's -

 

neither my magellan nor the Etrex will show position on 2 birds - the instructions say about the same for the Magellan.

 

wide open areas, tops of hills, and higher altitudes increase the ability to get more birds.

 

low areas - trees! - hills - urban jungles (tall buildings) all block signals and chance for wider spread of birds.

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On a cache I did several months ago in the mountains of WA state I could not get a lock with 3 sats. on my Ledgend. I had a good strong signal on 3 sats. and even pulled out my external antenna and still could not grab that 4th sat. It took 20 mins sitting on a rock in the open to finally get that 4th and a lock. When it finally locked on I saw that I was only 80 ft from the cache. I now have a 60cs and driving across E.WA with a clear view of the horizon in all directions I had 14 sats. The 150 or so caches I've done with my 60cs I've yet to lose a signal, so I've been very impressed with that.

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AJK was correct on the reason you need 4 satellites to get a lock. It needs 4 readings to solve 4 equations (X, Y, Z and Time). So three satellites would give you the position (X, Y, and Z), and the fourth corrects the time.

 

Beta Test: It is not possible to pick up 20 satellites simultaneously with the Rino 120. First of all, the satellite orbits are designed in such a way that at least 4 satellites will be visible at all time for any location on the earth. There are 24 active satellites (plus 2 for WAAS), so even in the open skies of the prairies, I doubt that you would be able to see 20 of the 26 satellites at one time.

 

Secondly, the Rino 120 is a 12 parallel channel GPS receiver. That means it can track up to 12 satellites at one time. So even if it were possible to see 20 satellites, your GPS could only lock onto 12 of them.

 

I picked up 12 satellites on my Garmin Legend one day here in Rochester, NY. It was in the middle of the afternoon and I had a clear view of the sky. It was such a rare thing, I even took a picture:

 

66389_500.jpg

 

Generally, I find that the evening is the best time around here for picking up the most satellites.

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I have an eTrex Vista. I regularly get 5-6 satellites. Usually 7-8 on clear days. Most of the time I have no. 35 WAAS. Before I got my GPS, I read some very useful information on the Trimble website. It goes into great detail explaining the GPSystem. My manual for my Vista says that the WAAS is still experimental, and may not be fully functional. When I have that no. 35 locked on, my GPS has had an accuracy reading as low as 14'. Does anyone know if the WAAS is now fully functional??

 

I am in NE Pennsylvania.

Edited by meisterjd1
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I have an eTrex Vista. I regularly get 5-6 satellites. Usually 7-8 on clear days. Most of the time I have no. 35 WAAS. Before I got my GPS, I read some very useful information on the Trimble website. It goes into great detail explaining the GPSystem. My manual for my Vista says that the WAAS is still experimental, and may not be fully functional. When I have that no. 35 locked on, my GPS has had an accuracy reading as low as 14'. Does anyone know if the WAAS is now fully functional??

 

I am in NE Pennsylvania.

Just having a lock on a WAAS SV doesn't mean you've got correction data. You've got to look for the indicator (a "D" on Garmin units) for the other satellites. If you don't get at least 4, you're not using WAAS. If you're just getting an accuracy read of 14', you're probably not. That's easily attainable without WAAS turned on.

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With the old GPS 45, I was lucky to see 5 sats with the 1 channel receiver. Now, 8 is probably average and I get the WAAS correction more often than I ever thought would be possible.

 

You need 4 sats for the time correction as stated above, but you also need 4 to get a 'Point'.

 

One sat tells the receiver you are X distance from the sat. That number defines a sphere the radius of X.

 

The second sat provides another sphere and where the two intersect is a circle.

 

The third sat adds another sphere and where all three intersect is 2 points.

 

The fourth sat's sphere will only intersect at one of the two points. The reason that the altitude is such a problem is that most of your signals will be comong straight down and the circle intersections are not all that far apart. virtically. It is the few near horizon signals that really help the altitude calculations. If you have 3 signals and they are all nearly overhead, the virtical difference in the two points could be only a few hundred feet. The unit can not determine which is the correct one.

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I have found that WAAS is hard to get a lock on with an internal antenna. I am guessing because it needs good reception to download the corrected date.

 

However, when I am in my car and use my patch antenna, WAAS gets a strong lock and I have D's on all my sats within 2 minutes, and accuracy of about 4 meters.

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Just this afternoon here in Bremerton, WA. I decided I should let my 76C acquire satellites for a while. I set my external antenna on top of my carport and run the lead down to a stepladder. I also enabled WAAS and was running on external power supply. Within 20 minutes I was getting full scale on all bars with D on them. I was also getting number 47 WAAS satellite also with a D on it. It was indicating 6 feet. Without the external antenna it indicated 8 feet and I lost number 47. Never have seen anything on the other WAAS satellite, number 35. Now if I can get half that good this week when I go for my 700 milestone cache, Half Moon in SW Washington. Dick, W7WT

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First of all:

Maybe it would be a little more helpful if we include our GPSr model and conditions!
No it won't! Any standard unit will do pretty much what the next one will do, at the same time and place. The "conditions" that matter are up above, and pretty much out of your control.

 

As far as rain, the experts say it shouldn't bother you much - however a relatively thin cover of water over your car can bother you in a solid sheet. So hard rain will. A cloudy day should not bother you. But invisible "atmospheric stuff" will.

 

I used to be concerned with only 4 satellites. That's a low day for me, seems like, but it works just fine. The days when I can't get accuracy under 20' are rare.

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There is only space for twelve satellites on the display screen of my, well used, Rino 120.

Usually we get 4-8 including #47 WAAS. A couple weeks ago, on the side of a mountain wilderness area, during the afternoon of a crystal clear day, ten sats were locked in big time. The WAAS, was nowhere to be seen. I was on the east slope of the mountain and had already found the cache.

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Thanks everybody and now that we have all these replies I have another question that someone brought up.

 

External antenna. I have a 60CS and with all of the lost signals that I get I was thinking about this but from some of what I read you need a power source?

 

What external antennas do you recommend?

 

Thanks,

 

Marshall

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