Magellan 300 enter wrong time to optimize satalite tracking

[Guest ferdinand]

I just got a Magellan 300. Entered the time and date. It seemed to have a difficult time tracking satalites. With this model you need at least 3 satalites to update data. I entered the wrong on purpose (shifted ahead by one hour). Maybe there is a time that is even better? Has anyone set different times to optimaze tracking

[Guest ferdinand]

oh, yea. when I entered the wrong time, it very quickly picked up 4 satalites, which was an improvement. It also worked better trecking thru the woods.

[Guest Mike_Teague]

as soon as you get a lock, it will automatically set the time anyhow, so I cant see how it will make any difference..

 

thats another part of teh GPS service, position AND precise time

[Guest Jude from New Brunswick]

What does the time have to do with satelites?Would daylight saving time affect the positions that the satelites are at that time of day in the sky?

 

JuDe

[Guest ferdinand]

Mike, I check the time on my Magellan 300. After I made good satalite tracking it did not update the time. I'm returning it to the store and bying a different model.

[Guest Mike_Teague]

the unit doesn't know which time zone you're in, if you display UTC and change it, I wager it will indeed correct itself once locked.

[Guest Seamus]

quote:

---

Originally posted by Jude from New Brunswick:

What does the time have to do with satelites?

---

 

Time has everything to do with how GPS works. The satellites all contain atomic clocks, which keep accurate time down to of a second. The signal they transmit is essentially just "The time is now 09:47, GMT...tick...tick...tick...tick". GPS units receive these signals, slightly off-frequency and delayed, due to doppler shift and their position in the sky (and atmospheric effects, which introduce errors). The processor inside the GPS unit interprets these signals, works the geometry in reverse, and figures out exactly where you would have to be in order to receive exactly that combination of signals (actually, it resolves two points, one on the surface of the Earth, and one way out in space -- it assumes you aren't in space). It knows the exact time because the satellites are continually announcing it, and updates its internal clock accordingly.

 

Hope this helps explain a bit.

...and if I got anything wrong, keep in mind -- I'm a helpdesk tech, not a GPS and satellite navigation guru.

 

-- Seamus

KC5UGQ

Frederick, MD

[Guest JuDe]

Correct.So,why do I have 12 satellites showing on my GPS at 04:00 UTC and only seven at 16:00 UTC??Some are missing or to weak or maybe the weather would play a factor like Seamus said ???

[Guest bob_renner]

when you first turn on your receiver, before it locks on to the sats and figures out where it is, it uses the following information:

 

1. The time (UTC)

2. The last recorded sat almanac (where the sats are above the earth)

3. Its last known position.

 

From this it can determine what sats should be visible and can display the sky view.

 

If the receiver has been moved since it was last used and it thinks it's someplace other than where it really is, then it will take longer to lock on to the sats than usual. The garmin manual says if the receiver has moved more than 500 miles, then it will need to do an autolocate. If it can't determine where it is, you can tell it what country/state you're in to speed up the lock.

 

Bob

[Guest ferdinand]

A wager? Mike, I accept your wager and anti 1 beer. If I win I prefer Anchor Steam. I will try my GPS receiver (Magellan 300) tonight. What I think I have observed so far is setting the time changes the satalite map displayed, it also seems to change it's performance (how well it tracks satalites and its ability to lock on). Also when I do get 3 or more satalites locked on and an active tracking signalis indicated it does not update the clock that is displayed, perhaps there is an internal clock? I will put the receiver into UTC mode to see what that does, now it is set to 12 hour.

 

Thanks, Jim

[Guest Mike_Teague]

Indeed if you mis-set the clock, you will initially get a different sat view screen.. it WILL delay the initial lock because it will be looking for sats that arent visible, and not looking for those that are visible..

After it gets a decent lock though, let it sit for a while.. it should reset itself.. why it's not doing it instantly is a mystery to me, I'd let it sit for a good 15 minutes though... with more than 3 sats..

 

missetting the clock should have no different an affect than intentionally telling it youre several hundred miles away from where you actually are... of course it will take longer to get a lock, but once you got one, it will tell you the correct position...

 

Time is no different..

[Guest bsyris]

Hmmm... Perhaps the unit needs to see more than 3 sats(the mininum to get a fix) to update the time? This seems a likely problem with way the Magellan operates, though.

[Guest ferdinand]

Further experiments have been conducted. Magellan 300. I went to set up and found the UTC time to be different than the displayed 12 hour time that I initially set. It does update its UTC time after it makes a 3 satalite lock and begins tracking it does not update the 12 or 24 hour clock.

 

I have been told the Garmin uses an offset from UTC time to set the displayed 12 hour time, which sounds like a much better method.

 

thank to everybody for their input.

 

Jim

[Guest Mike_Teague]

You owe me a beer

[Guest Mike_Teague]

You owe me a beer