Time Of Day And Signal Strength?

[+rogueleader1977]

I thought of this because of a question about cloud cover in another forum. I've noticed that in the late evening no matter what the cloud cover, I have mch better accuracy. We're talking 10 feet or less. Most of the time my explorist 210 usualy avarages 20 feet or more. Is there any truth behind this or is it just my imagination?

[+BadAndy]

Remember that the GPS works on radio transmissions.

 

Many hams can tell you about radio waves and daylight hours.

 

Heres something I found about it.

 

The ionosphere and radio waves.

[+Prime Suspect]

It may just be that there's a particularly good constellations of satellites around that time. Because of the timing of the orbits, constellations repeat at nearly the same time every day (twice a day, actually). Every day, the exact constellation recurs every 11 hours and 58 minutes.

[+paintfiction]

It may just be that there's a particularly good constellations of satellites around that time. Because of the timing of the orbits, constellations repeat at nearly the same time every day (twice a day, actually). Every day, the exact constellation recurs every 11 hours and 58 minutes.

 

I was under the impression that the GPS satellites were in geo-synchronous orbit which should make the stationary relative to us. Not correct?

[+Stunod]

It may just be that there's a particularly good constellations of satellites around that time. Because of the timing of the orbits, constellations repeat at nearly the same time every day (twice a day, actually). Every day, the exact constellation recurs every 11 hours and 58 minutes.

 

I was under the impression that the GPS satellites were in geo-synchronous orbit which should make the stationary relative to us. Not correct?

 

Not correct.

 

Only the WASS sats are geo-synchronous

Edited June 7, 2006 by Stunod

[+BadAndy]

It may just be that there's a particularly good constellations of satellites around that time. Because of the timing of the orbits, constellations repeat at nearly the same time every day (twice a day, actually). Every day, the exact constellation recurs every 11 hours and 58 minutes.

 

I was under the impression that the GPS satellites were in geo-synchronous orbit which should make the stationary relative to us. Not correct?

 

The 2 WAAS sats are in geosync orbit, the rest are not

[+nekom]

Though not in geosynch, I think they're in a high orbit (higher than weather sats), but I could be wrong. I thought I read somewhere that at any point on earth, there are always at least 4 in range. Again, could be wrong. I've never made much sense of it myself, but there have been times when I was dead on, and times when I was 150 feet or more off on accuracy.

[+Stunod]

Though not in geosynch, I think they're in a high orbit (higher than weather sats), but I could be wrong. I thought I read somewhere that at any point on earth, there are always at least 4 in range. Again, could be wrong. I've never made much sense of it myself, but there have been times when I was dead on, and times when I was 150 feet or more off on accuracy.

 

They orbit at about 12,000 miles.

[+rogueleader1977]

Thanks! I too thought that it would have something to do with the constelation of satelites. Then I was also thinking that the satelites were always in the same position. But that makes sense now that I think about it.

[+The Geocache Hunter]

Although the satellites move in thier orbit and the amount of coverage you have varies quite a bit I have to wonder if the military can place them where they want them? Every once in awhile, here in Colorado, I struggle to pick up three satellites. I recently got back from a tour in Iraq and I always had atleast a dozen satellites available all the time throughout the entire year.

[+EScout]

There are ways of seeing the quality of the constellation, and your position.

 

Trimble Planning Software

 

The DOP page will show you a graph with times of high and low DOPs.

[+fizzymagic]

The actual answer to the OP's question is that at night, when the sun is down, the ionosphere is quiet. If you are not using WAAS, your accuracy estimates will be lower if your unit is intelligent enough to take the error in the ionospheric model into account. If you are using WAAS, there shouldn't be much difference.

[+Prime Suspect]

Although the satellites move in thier orbit and the amount of coverage you have varies quite a bit I have to wonder if the military can place them where they want them?

No.

[+The Geocache Hunter]

I guess Iraqi Geocachers are just lucky to have a sky full of satellites all the time. It just seems odd to me to have atleast a dozen 24 hours a day all year long when I occasionally struggle to find enough to get a reading here in the States. Wish I had paid more attention to the satellite numbers I was receiving, maybe there are a couple that are always there.

[+Prime Suspect]

I guess Iraqi Geocachers are just lucky to have a sky full of satellites all the time. It just seems odd to me to have atleast a dozen 24 hours a day all year long when I occasionally struggle to find enough to get a reading here in the States. Wish I had paid more attention to the satellite numbers I was receiving, maybe there are a couple that are always there.

It probably has a lot more to do with the terrain, than anything else.

[+The Geocache Hunter]

A current almanac reading on your GPSr will still tell you that a satellite is there even if terrain prevents you from receiving a signal from it. Sometimes there are a bunch in the sky, sometimes there are only a couple, sometimes I can receive signals from most of them, sometimes I can only get a few.

[+Maclir]

I have had my suspicions about the military concentrating satellites over certain locations. I typically get around 15 feet of accuracy on my Garmin E-trex. BUt 18 months ago, on a road trip across New Mexico, we drove past the White Sands misslie range - indicated accuracy was 5 feet....

 

Now, back on the question of ionosphere and reception - I would have thought the frequency in use would habe been much higher than those the ionosphere can impact.

[+BadAndy]

I have had my suspicions about the military concentrating satellites over certain locations. I typically get around 15 feet of accuracy on my Garmin E-trex. BUt 18 months ago, on a road trip across New Mexico, we drove past the White Sands misslie range - indicated accuracy was 5 feet....

 

Now, back on the question of ionosphere and reception - I would have thought the frequency in use would habe been much higher than those the ionosphere can impact.

 

Repositioning the orbit of a satellite isn't something thats easily done. There are no trees, buildings or cliffs at White sands. Nothing but big open sky. Couple that with a good constellation and a waas signal and 5 feet is about right.

[+oscar478]

I guess Iraqi Geocachers are just lucky to have a sky full of satellites all the time. It just seems odd to me to have atleast a dozen 24 hours a day all year long when I occasionally struggle to find enough to get a reading here in the States. Wish I had paid more attention to the satellite numbers I was receiving, maybe there are a couple that are always there.

 

Not to mention the possible locations... how incredibly cool would it be to have an extra large geocache... Say something along the size of an abandoned Iraqi tank?

 

And some bomb/missle craters would allow for burying of some large caches w/o ever touching a shovel.

 

On the contrary, there probably isn't a worst place in the world to place an odd looking container near a road or a path. Being muggled is one thing... being presumed to be an IED and demolished is another.

[mandygus]

Since the co-ords accuracy is variable..who wants it spot on? is there a case for puttiing a note on the cache page, or even as a required info, the accuracy of the reading taken? Helpful for the occasions when 15 mins averaging cannot improve on +/- 12 m ..say , or whatever .?

Edited June 12, 2006 by mandygus

[+Prime Suspect]

I have had my suspicions about the military concentrating satellites over certain locations. I typically get around 15 feet of accuracy on my Garmin E-trex. BUt 18 months ago, on a road trip across New Mexico, we drove past the White Sands misslie range - indicated accuracy was 5 feet....

 

Now, back on the question of ionosphere and reception - I would have thought the frequency in use would habe been much higher than those the ionosphere can impact.

GPS satellite propulsion systems are designed to make small, precise orbital corrections. They can't go zipping around space like you see in movies. They have a limited amount of propellant that has to last the lifetime of the SV.

[+Team Cotati]

I have had my suspicions about the military concentrating satellites over certain locations. I typically get around 15 feet of accuracy on my Garmin E-trex. BUt 18 months ago, on a road trip across New Mexico, we drove past the White Sands misslie range - indicated accuracy was 5 feet....

 

Now, back on the question of ionosphere and reception - I would have thought the frequency in use would habe been much higher than those the ionosphere can impact.

GPS satellite propulsion systems are designed to make small, precise orbital corrections. They can't go zipping around space like you see in movies. They have a limited amount of propellant that has to last the lifetime of the SV.

 

You mean to tell me that they don't use the space shuttle to go up there and grab 4 or 5 at a time and haul them to Iraq?

[+Team Cotati]

I have had my suspicions about the military concentrating satellites over certain locations. I typically get around 15 feet of accuracy on my Garmin E-trex. BUt 18 months ago, on a road trip across New Mexico, we drove past the White Sands misslie range - indicated accuracy was 5 feet....

 

Now, back on the question of ionosphere and reception - I would have thought the frequency in use would habe been much higher than those the ionosphere can impact.

GPS satellite propulsion systems are designed to make small, precise orbital corrections. They can't go zipping around space like you see in movies. They have a limited amount of propellant that has to last the lifetime of the SV.

 

You mean to tell me that they don't use the space shuttle to go up there and grab 4 or 5 at a time and haul them to Iraq? I seem to recall a james bond movie where they did that.

Edited June 12, 2006 by Team Cotati