Re: [time-nuts] Survey plot as art.
gem@rellim.com said:
In my case (the original post) there can be no multipath difference,
same antenna and done at the same time.
There sure can be. The GPS birds are moving in orbit. At certain points in
the sky their signal may be bouncing off a nearby steel building and into
your antenna.
He didn't say no multipath, but rather no multipath difference. He's feeding
2 GPS units from the same antenna through a splitter.
--
These are my opinions. I hate spam.
Yo Hal!
On Sat, 07 Jan 2017 14:16:16 -0800
Hal Murray hmurray@megapathdsl.net wrote:
gem@rellim.com said:
In my case (the original post) there can be no multipath
difference, same antenna and done at the same time.
There sure can be. The GPS birds are moving in orbit. At certain
points in the sky their signal may be bouncing off a nearby steel
building and into your antenna.
He didn't say no multipath, but rather no multipath difference. He's
feeding 2 GPS units from the same antenna through a splitter.
Ah. Got it. Thank you.
Same model GPS?
RGDS
GARY
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
gem@rellim.com Tel:+1 541 382 8588
Veritas liberabit vos. -- Quid est veritas?
"If you can’t measure it, you can’t improve it." - Lord Kelvin
Yo All!
I just ran 24 scatter plots on 2 GPS with external antennas one inch apart.
pi2-5.png is an Adafruit GPS HAT with an MTK-3301. upuv2.png is an
Uputronics GPS HAT version 2, with a uBlox 8.
See attached. I'm not sure it sheds any light on this discussion...
There does appear to be a bit of correlation between the bigger random
walks in the graphs. And a whole lot of other things going on.
During that time, the Adafruit saw 6 to 12 sats and a constant TDOP of
0.82. The Uputronics reported seeing 4 to 20 sats and a TDOP from 0.42
to 32.6 and a mean of 0.786 and a SD of 0.668.
To bring this back to time-nuttery, when the TDOP hit 32.6 I can see a
2 micro Second spike in NTP jitter. So for that small period in time
my Raspberry Pi clock was more stable than my PPS.
RGDS
GARY
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
gem@rellim.com Tel:+1 541 382 8588
Veritas liberabit vos. -- Quid est veritas?
"If you can’t measure it, you can’t improve it." - Lord Kelvin
Gary
Only 1" ? (1" center to center or edge to edge spacing?)
My gut reaction is that "coupling" between the two antennas may have
some effect on some of the variation. You may in fact have
unintentionally created a phased array. This phased array could favor
one antenna in an particular Az/El and favor the other in another Az/El.
If not too arduous it would be good to separate the antennas by several
feet, run the data again then swap mountings of the antennas and run yet
another set of data
Dave
On 1/8/2017 4:52 PM, Gary E. Miller wrote:
Yo All!
I just ran 24 scatter plots on 2 GPS with external antennas one inch apart.
pi2-5.png is an Adafruit GPS HAT with an MTK-3301. upuv2.png is an
Uputronics GPS HAT version 2, with a uBlox 8.
See attached. I'm not sure it sheds any light on this discussion...
There does appear to be a bit of correlation between the bigger random
walks in the graphs. And a whole lot of other things going on.
During that time, the Adafruit saw 6 to 12 sats and a constant TDOP of
0.82. The Uputronics reported seeing 4 to 20 sats and a TDOP from 0.42
to 32.6 and a mean of 0.786 and a SD of 0.668.
To bring this back to time-nuttery, when the TDOP hit 32.6 I can see a
2 micro Second spike in NTP jitter. So for that small period in time
my Raspberry Pi clock was more stable than my PPS.
RGDS
GARY
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
gem@rellim.com Tel:+1 541 382 8588
Veritas liberabit vos. -- Quid est veritas?
"If you can’t measure it, you can’t improve it." - Lord Kelvin
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
--
Dave
Manuals@ArtekManuals.com
www.ArtekManuals.com
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus
Yo Artek!
On Sun, 8 Jan 2017 17:18:06 -0500
Artek Manuals Manuals@ArtekManuals.com wrote:
Only 1" ? (1" center to center or edge to edge spacing?)
One inch edge to edge.
My gut reaction is that "coupling" between the two antennas may have
some effect on some of the variation.
I have tried many various combinations over the last 6 months. using
6 diferent GPS. Before that I took some GPS to an open field. Also
friends of mine have run gpsprof and gotten similar. All look pretty
much like these, modulo the different GPS chips.
gpsprof is part of the gpsd package, feel free to do yooou own plots.
RGDS
GARY
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
gem@rellim.com Tel:+1 541 382 8588
Veritas liberabit vos. -- Quid est veritas?
"If you can’t measure it, you can’t improve it." - Lord Kelvin
On Mon, Jan 9, 2017 at 5:52 AM, Gary E. Miller gem@rellim.com wrote:
I just ran 24 scatter plots on 2 GPS with external antennas one inch apart.
pi2-5.png is an Adafruit GPS HAT with an MTK-3301. upuv2.png is an
Uputronics GPS HAT version 2, with a uBlox 8.
The Adafruit plot seems to have quantization. Are the values being
"snapped" to a grid in any way?
--
Sanjeev Gupta
+65 98551208 http://www.linkedin.com/in/ghane
Hi Gary,
Yo Artek!
On Sun, 8 Jan 2017 17:18:06 -0500
Artek Manuals Manuals@ArtekManuals.com wrote:
Only 1" ? (1" center to center or edge to edge spacing?)
One inch edge to edge.
My gut reaction is that "coupling" between the two antennas may have
some effect on some of the variation.
For high accuracy applications, I have been given the advice to keep GPS
antenna separation much higher. 1 meter separation was suggested.
For comparing GPS receiver behavior its a cleaner setup to use a GPS
signal splitter (or basic RF splitter with suitable DC-blocks).
--
Björn
Yo Björn!
On Mon, 9 Jan 2017 07:45:00 +0100
"Björn Gabrielsson" bg@lysator.liu.se wrote:
My gut reaction is that "coupling" between the two antennas may
have some effect on some of the variation.
For high accuracy applications, I have been given the advice to keep
GPS antenna separation much higher. 1 meter separation was suggested.
Clearly the Adafruit is not high accuracy. I have played with some
short baseline DGPS (cm level data) and not found any issue with antenna
separation.
For comparing GPS receiver behavior its a cleaner setup to use a GPS
signal splitter (or basic RF splitter with suitable DC-blocks).
Care to recommend any that have SMA connectors? I have found that
a 3dB difference in antenna can degrade my data quality, it would be
interesting to see how the 3dB loss of the splitter affects thins.
RGDS
GARY
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
gem@rellim.com Tel:+1 541 382 8588
Veritas liberabit vos. -- Quid est veritas?
"If you can’t measure it, you can’t improve it." - Lord Kelvin
Hi Gary,
My gut reaction is that "coupling" between the two antennas may
have some effect on some of the variation.
For high accuracy applications, I have been given the advice to keep
GPS antenna separation much higher. 1 meter separation was suggested.
Clearly the Adafruit is not high accuracy. I have played with some
short baseline DGPS (cm level data) and not found any issue with antenna
separation.
Good for you! Others have found issues.
For comparing GPS receiver behavior its a cleaner setup to use a GPS
signal splitter (or basic RF splitter with suitable DC-blocks).
Care to recommend any that have SMA connectors? I have found that
a 3dB difference in antenna can degrade my data quality, it would be
interesting to see how the 3dB loss of the splitter affects thins.
The ZAPD-2DC+ from Minicircuits are good value for money, if 2 ports are
enough.
The Colorado based "GPS Source" and "GPS Networking" both provide quality
products. They have versions with SMA, but also TNC or N.
Splitters build for GPS use can be passive, but they are often amplified.
They will also pass power up to the lna in the antenna.
--
Björn
http://194.75.38.69/pdfs/ZAPD-2DC+.pdf
https://www.gpsnetworking.com/store
https://www.gpssource.com/products/s18s-1x8-slimline-gps-splitter
Hi Gary,
Clearly the Adafruit is not high accuracy. I have played with some
short baseline DGPS (cm level data) and not found any issue with antenn separation.
I'm surprised by your claim. My measurements show that the Adafruit is a wonderful GPS receiver. Attached are ADEV MDEV TDEV plots of 5 different GPS/1PPS receivers. The raw data is from:
http://www.leapsecond.com/pages/gpsdo-sim/
The Adafruit "Ultimate GPS" (MTK3339 chipset) does very well. It's also cheap, has a built-in antenna, has a uFL connector for optional external antenna, runs in 3D so you can use it mobile or fixed, you don't have to bother with survey or sawtooth correction. The data you see above is out-of-the-box; you give it 5V and out comes a 1PPS:
https://www.adafruit.com/product/746
/tvb