GPS Satellites Visible But No Fix

[Nishanth]

Hi,
I am using Quectel L86 GPS Module, I am facing following problems:-
1. GPS Satellite Fix takes more time or sometimes not at all fixing. (Even using external chip Antenna problem exists)
2. Which of these following satellites, I need to enable:- (All I need to enable or according to my location I need to turn ON/OFF)
* GALILEO_FULL_Enable
* GALILEO_Enable
* GLONASS_Enable
* GPS_Enable
3. Even in 12-15 Satellites View also.... The GPS not giving same location repeatedly..It is giving different lat&log every 2-3 minutes....
4. When wanted to use HOT,WARM,COLD Starts.
5. After these Starts, Even though I didn't get satellite connectivity. How long, I need to wait to resend these Start commands.

Thanks

 

[davenn]

1. GPS Satellite Fix takes more time or sometimes not at all fixing.

I don't know if you understand you are not using the correct terminology ? you CANNOT get a FIXED location with a single unit
so what do you REALLY mean ?

3. Even in 12-15 Satellites View also.... The GPS not giving same location repeatedly..It is giving different lat&log every 2-3 minutes....

how different are the LAT and LONG ? .... be specific

 

[Nishanth]

I don't know if you understand you are not using the correct terminology ? you CANNOT get a FIXED location with a single unit
so what do you REALLY mean ?



how different are the LAT and LONG ? .... be specific

LAT and LONG -15 to 20 meters difference
In NMEA PROTOCOL
GSV:- SATELLITE IN VIEW:-15 TO 20
GGA:- POSITION FIX:- INVALID

 

[davenn]

LAT and LONG -15 to 20 meters difference
In NMEA PROTOCOL

around 10 - 15 is the best you would ever get, anywhere between 10 and 20m would be typical for a single unit

GGA:- POSITION FIX:- INVALID

well that is correct as I stated previously

you CANNOT get a fixed location with only one unit



I do hi precision Trimble GPS for my job, to get less that 10 metres accuracy and to get a FIXED location requires much better
technology than a simple car or handheld receiver

 

[(*steve*)]

We'll... You can also average over time. That's what my GPS disciplined frequency standard does. The accuracy of the reference frequency is partially based on it knowing where it is with respect to the satellites. While it can get an approximate value quickly, it improves over time (up to a week allegedly) as it fine tunes it's actual location.

 

[kellys_eye]

What positional accuracy are you seeking? GPS accuracy is deliberately degraded - it's a military system after all .

Precision position accuracy (centimetric) is expensive and uses differential correction systems.

Select ONE system and see if that makes a difference.

 

[(*steve*)]

GPS accuracy is deliberately degraded -

I believe selective availability is turned off these days (since May 2000 by a decision on the Clinton white house).

And future satellites may not even have the capability included.

 

[kellys_eye]

Wow - that long ago! How time flies!

 

[davenn]

I believe selective availability is turned off these days (since May 2000 by a decision on the Clinton white house).

And future satellites may not even have the capability included.

Wow - that long ago! How time flies!

yes, that is true

there are just a speed and height restrictions in place

As I said up the page, I do high precision GPS for my main job
our precision accuracy is down to 3mm horiz and 7mm vertical
vertical accuracy is always at least twice as "poor" as horizontal.... it's just the way GPS works

 

[davenn]

GGA:- POSITION FIX:- INVALID

here's an example of a good quality FIXED position I am used to getting .........

 

[Ylli]

3mm, that translates to a time accuracy of 10 ns or better. That deserves a WOW.

 

[kellys_eye]

I recently bought some extra land adjacent to my property and during the negotiation process the sellers wanted me to pay for centimetric GPS surveying to establish the boundaries.

I got a tape measure out and did it manually and saved a few 100££. I had to - when I told them I wasn't paying for GPS surveying they sent a couple of goons to do a manual measurement but they didn't know HOW.

What's the education system coming to these days?????

Cool accuracy on those GPS results though Dave!

 

[davenn]

3mm, that translates to a time accuracy of 10 ns or better. That deserves a WOW.

indeed ... seriously impresses me every day

What's the education system coming to these days?????

yeah ... totally reliant on computer systems !

Cool accuracy on those GPS results though Dave!

thanks ......

without hijacking the thread too much, here's an overview of the system above for obtaining high accuracy ......

That above screen show is one of these ... a CB460 Machine control, control box,



these sit in a dozer, grader, excavator etc and is the control hub for all the sensors receivers etc



the guts of the system is a GPS base station in the construction site hut that broadcasts GPS corrections out on 450-460 MHz.
The SNRx10 you see on the right receives those signals and sends them to the CB460 (450) along with GPS data from one or two GPS dome receivers
as seen in the upper centre (MS992)

when those 2 sets of GPS data are combined in the control box, a high accuracy FIXED location can be derived.

And this is what I was trying to impress upon the OP @Nishanth ...... good or high accuracy cannot be obtained by a single budget GPS receiver.
The best you can get is around 10m ( 10 - 20m avg)

I don't install this gear on machines, the company has installation and support guys for doing that. Rather those items come into my workshop for repair

Dave

 

[kellys_eye]

I recall installing DGPS systems on ships a few decades ago. These relied on separate receivers to pick up correction signals sent from fixed base station on land. Such systems were fitted a part of DSP (dynamic ship positioning) systems such as mobile rigs and tasks like dropping sea anchors accurately.

Can't recall what frequency the Differential part worked on - ISTR it was 425kHz ??? Or thereabouts. To long ago for this old brain to recall....