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Cheapest DGPS receivers

L

linnix

Jan 1, 1970
0
How about this:

If we have all day to track 100 positions and
looking for the cheapest solution.

We install 100 remote receivers (micro + RF) and
sample the IF (20 to 30 MHz) for 10 to 20 seconds
(100 MBytes)? We can transmit this with a slow
serial link to a central station.

We can then process this 10G data in DGPS mode,
using the Philips's software solution.

Will this work?
 
L

linnix

Jan 1, 1970
0
OK, I guess we need to use a mobile rover,
using the new L2C signals.
Someone has done this without the L2C signal,
they claim to have cm accuracy.
There are currently 2 or 3 birds with L2C,
so we need to time the daily sampling windows.

The plan is to have two sets of dual frequencies
RF front ends (L1=1.5GHz L2=1.2GHz).
Using a micro, we can sample and store a couple
of seconds of the 1Mhz sub-carrier signals.
Differential measurements can be taken with
both mobile and stationary (fixed reference position)
samples together.

The samples would be WiFi'ed to a central computer
for post processings. We can even archive the 1G bytes
samples on DVD (3 to 4 days of samples), in case we
need to go back and recalibrate the data.

Any suggestions or comments?
 
T

Ted Edwards

Jan 1, 1970
0
linnix said:
OK, I guess we need to use a mobile rover,
using the new L2C signals.
Someone has done this without the L2C signal,
they claim to have cm accuracy.
There are currently 2 or 3 birds with L2C,
so we need to time the daily sampling windows.

The plan is to have two sets of dual frequencies
RF front ends (L1=1.5GHz L2=1.2GHz).
Using a micro, we can sample and store a couple
of seconds of the 1Mhz sub-carrier signals.
Differential measurements can be taken with
both mobile and stationary (fixed reference position)
samples together.

The samples would be WiFi'ed to a central computer
for post processings. We can even archive the 1G bytes
samples on DVD (3 to 4 days of samples), in case we
need to go back and recalibrate the data.

Any suggestions or comments?
Any WAAS enabled GPSR would give you 2 meter accuracy on a good day if
you averaged for a couple of minutes. This assumes that that is good
enough (you don't sat what accuracy you need) and that you are in an
area with a decent sky view and can receive WAAS (you give no indication
where you are). Waypoints will store the location(s).
 
L

linnix

Jan 1, 1970
0
Ted said:
Any WAAS enabled GPSR would give you 2 meter accuracy on a good day if
you averaged for a couple of minutes. This assumes that that is good
enough (you don't sat what accuracy you need) and that you are in an
area with a decent sky view and can receive WAAS (you give no indication
where you are). Waypoints will store the location(s).

Yes, we have WAAS enabled. The sky is clear.
We want 0.1 meter accuracy. Someone did a terrain
mapping within a couple of cm with DGPS,
using L2 (military band) sub-carrier corrections.
I think that's how they make survey grade GNSS.

I believe we can make use of the new L2C (civilian band) codes
for similar result. We don't need to process the data immediately,
just to log enough information for later processing. We can tap
into the L1 signal from a standard GPS. My question is whether
we can use a different crystal and get the L2 signal?
 
I

Iwo Mergler

Jan 1, 1970
0
linnix said:
How about this:

If we have all day to track 100 positions and
looking for the cheapest solution.

We install 100 remote receivers (micro + RF) and
sample the IF (20 to 30 MHz) for 10 to 20 seconds
(100 MBytes)? We can transmit this with a slow
serial link to a central station.

We can then process this 10G data in DGPS mode,
using the Philips's software solution.

Will this work?

Yes. In fact, if you chose your frontend wisely,
you only need to sample about 10MBits/sec - 2 bits
@ 5MHz. It's not an easy job though. You may want
to talk to NXP (Ex-Philips Semiconductors) first,
before investing a lot of work in this.

However, unless you are planning to make thousands
of mobile devices, it's probably cheaper (and lower power)
to find a complete GPS chipset which outputs
pseudo-ranges.

Kind regards,

Iwo
 
L

linnix

Jan 1, 1970
0
Iwo said:
Yes. In fact, if you chose your frontend wisely,
you only need to sample about 10MBits/sec - 2 bits
@ 5MHz. It's not an easy job though. You may want
to talk to NXP (Ex-Philips Semiconductors) first,
before investing a lot of work in this.

However, unless you are planning to make thousands
of mobile devices, it's probably cheaper (and lower power)
to find a complete GPS chipset which outputs
pseudo-ranges.

The problem is finding a chipset for L2 (1.2G).
Some internal filters tuned to L1 (1.5G) would not work.

In additional, we want to use the NIST chip atomic clock (E-15
precision),
instead of the TCXO crystal (E-10 precision). This would elimate the
carrier phase unknown and simplify the PLL.

The atomic clock chip contains laser tuned cesium particles in silicon
wafer.
It does not seem too difficult to make. A Differential mode Atomic
Global
Positioning System (DA-GPS) would be perfect for us.
Is anyone working on the atomic clock, other than the NIST reseach
team?

Thanks.
 
M

MassiveProng

Jan 1, 1970
0
The problem is finding a chipset for L2 (1.2G).
Some internal filters tuned to L1 (1.5G) would not work.

In additional, we want to use the NIST chip atomic clock (E-15
precision),
instead of the TCXO crystal (E-10 precision). This would elimate the
carrier phase unknown and simplify the PLL.

The atomic clock chip contains laser tuned cesium particles in silicon
wafer.
It does not seem too difficult to make. A Differential mode Atomic
Global
Positioning System (DA-GPS) would be perfect for us.
Is anyone working on the atomic clock, other than the NIST reseach
team?

One big issue would be the band you intend on "transmitting to a
central location" with.

You'd better get a license, and get informed about what is
available, and at what power levels. Each station needs a power
supply too. Solar.
 
L

linnix

Jan 1, 1970
0
MassiveProng said:
One big issue would be the band you intend on "transmitting to a
central location" with.

You'd better get a license, and get informed about what is
available, and at what power levels. Each station needs a power
supply too. Solar.

One idea is to charge solar cells on stations with a high power laser.
Since the critical logging time is in bad weather, without sun light.
A laser (with warnings) could also deter unwanted visitors.

ISM at 900MHz should be more than enough bandwidth.
Initially, just a mobile rover to power up
the sensors and download the log. Hardwiring the stations at 115K
baud
serial link could work, if we can get enough atomic clocks. They said
the atomic clocks can be battery powered and with precision of a
hundredth
of a picosecond. All the atomic clocks could still be out of phase,
but at
a constant.

My question is whether anyone has reproduced the NIST result, and at
what cost?
 
C

Charlie Edmondson

Jan 1, 1970
0
One idea is to charge solar cells on stations with a high power laser.
Since the critical logging time is in bad weather, without sun light.
A laser (with warnings) could also deter unwanted visitors.

ISM at 900MHz should be more than enough bandwidth.
Initially, just a mobile rover to power up
the sensors and download the log. Hardwiring the stations at 115K
baud
serial link could work, if we can get enough atomic clocks. They said
the atomic clocks can be battery powered and with precision of a
hundredth
of a picosecond. All the atomic clocks could still be out of phase,
but at
a constant.

My question is whether anyone has reproduced the NIST result, and at
what cost?
If you are using lasers, then why all the BS about DGPS. You can use
the lasers directly to determine the distances between points to at
least mm accuracy. And no, if you are using a non-eye-safe laser, then
there is no way in hades you will be able to use them in a public
accesible place, even with warnings...

Charlie
 
L

linnix

Jan 1, 1970
0
Charlie said:
If you are using lasers, then why all the BS about DGPS. You can use
the lasers directly to determine the distances between points to at
least mm accuracy. And no, if you are using a non-eye-safe laser, then
there is no way in hades you will be able to use them in a public
accesible place, even with warnings...

OK, laser does not make sense at all. With laser measurements, you
have to do lots of manual works. The site is actually dangerous
enough
to keep the public away, except for the maintenance people.
Of course, they can turn off the power while working.
I guess high power voltage lines would be fine.
 
C

Charlie Edmondson

Jan 1, 1970
0
linnix said:
OK, laser does not make sense at all. With laser measurements, you
have to do lots of manual works. The site is actually dangerous
enough
to keep the public away, except for the maintenance people.
Of course, they can turn off the power while working.
I guess high power voltage lines would be fine.
Why dangerous? Talk to some of the geologists who watch volcanos and
earthquake faults. They set up laser monitoring stations all the time
that have to be unmanned but measured in mm accuracy. You should be
able to buy this stuff 'off the shelf' somewhere!

Charlie
 
L

linnix

Jan 1, 1970
0
Charlie said:
Why dangerous?

That's all relative. Mudslide is no big deal for geologists and us,
but it's dangerous enough for the public and especially teenagers
fooling around in the area.
Talk to some of the geologists who watch volcanos and
earthquake faults. They set up laser monitoring stations all the time
that have to be unmanned but measured in mm accuracy.

To reposition the laser automatically over multiple points is not a
simple matter.
You should be able to buy this stuff 'off the shelf' somewhere!

Charlie

Same for GPS equipments, if you have the money to spend.
 
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