Re: [time-nuts] Survey plot as art.

[Andrew Rodland]

On Sun, Jan 15, 2017 at 6:23 AM, Andrew Rodland  wrote:
> Relatedly, and just for fun, here's a video I made several years ago
> from a few days worth of constellation status data out of a cheap SiRF
> receiver. It's interesting to see how the satellite geometry changes
> over time... or maybe it's just fun to watch the pretty colors. If
> you're observant you can also get an idea for where the tall trees
> were at my old apartment and maybe my approximate latitude.
>
> The projection is stereographic from the nadir (I think), with 90°
> elevation at the center, 0° elevation at the edges, and north up. The
> "wiggles" near the edges are due to the granularity of the positions
> from the receiver (half-degree, IIRC). Points are drawn with size and
> brightness proportional to the log signal strength, and the trails
> fade out exponentially.
>

And here is the actual video:
https://www.youtube.com/watch?v=VZHK1c54YRk -- sorry about the
suspense.

Andrew
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Re: [time-nuts] Survey plot as art.

[Andrew Rodland]

On Sat, Jan 7, 2017 at 12:54 PM, Peter Reilley  wrote:
>
> This is the survey from my Trimble NTBW50AA.   It looks like some bacteria
> floating around.

Relatedly, and just for fun, here's a video I made several years ago
from a few days worth of constellation status data out of a cheap SiRF
receiver. It's interesting to see how the satellite geometry changes
over time... or maybe it's just fun to watch the pretty colors. If
you're observant you can also get an idea for where the tall trees
were at my old apartment and maybe my approximate latitude.

The projection is stereographic from the nadir (I think), with 90°
elevation at the center, 0° elevation at the edges, and north up. The
"wiggles" near the edges are due to the granularity of the positions
from the receiver (half-degree, IIRC). Points are drawn with size and
brightness proportional to the log signal strength, and the trails
fade out exponentially.

Andrew
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Re: [time-nuts] Survey plot as art.

[Jay Grizzard]

I realize that, in theory, the designs for these things are relatively 
straightforward. Unfortunately, the *vast* majority of my experience is 
in the digital world, so the best I could probably do on my own is 
Frankenstein some hopefully-appropriate circuits together and hope the 
result is usable.


...that's a bit too luck-based for my tastes, so I was hoping someone 
had already put something appropriate together that I could just lay out 
and build. I'm actually a bit surprised that (apparently)  nobody on 
this list has done so, given how many GPSs we all must collectively own...


(...anybody want to? I'll fund the PCB & components for you to test your 
design...)


-j


The standard design is pretty simple:

1) DC bias coupler on the input
2) Protection on the input
3) Saw filter on the input (say -3 db)
4) Fairly normal (Mini Circuits) low noise amp with appropriate gain (say 12 to 
18 db)
5) two way splitter for the two banks of outputs (-3db)
6) two way splitter to each output (-3db)
(obviously a 4 output device)
7) 3 db  (to 9 db) pads on each output
8) DC blocks on all but one output.
9) DC bias coupler on the one “magic” output.

Some designs put a second filter after the amp. Some designs use ceramic 
filters rather than SAW’s.
Some designs go up to quite a few (like a dozen) outputs. Some have external 
power rather than
the bias pickoff / pass thru.



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Re: [time-nuts] Survey plot as art.

[Stephen Tompsett]

This might be of use/interest for a GPS distribution amplifier:

http://huprf.com/huprf/wp-content/uploads/2016/03/DA1-4-Manual-V2_03.pdf


On 09/01/2017 23:27, Bob kb8tq wrote:
> Hi
>
>
>> On Jan 9, 2017, at 6:06 PM, Jay Grizzard  
>> wrote:
>>
>> Does anyone know of any schematics for amplified GPS splitters floating 
>> around out there? I looked a while back and couldn't find anything. I use a 
>> 58536A right now, but it's big and I hate having to have N to SMA cables.  
>> It would be awesome to be able to roll my own with all the connectors I want 
>> on it…
> The standard design is pretty simple:
>
> 1) DC bias coupler on the input
> 2) Protection on the input
> 3) Saw filter on the input (say -3 db)
> 4) Fairly normal (Mini Circuits) low noise amp with appropriate gain (say 12 
> to 18 db)
> 5) two way splitter for the two banks of outputs (-3db)
> 6) two way splitter to each output (-3db) 
> (obviously a 4 output device)
> 7) 3 db  (to 9 db) pads on each output
> 8) DC blocks on all but one output.
> 9) DC bias coupler on the one “magic” output. 
>
> Some designs put a second filter after the amp. Some designs use ceramic 
> filters rather than SAW’s.
> Some designs go up to quite a few (like a dozen) outputs. Some have external 
> power rather than
> the bias pickoff / pass thru.
>
> Bob
>
>> -j
>>
>> On 1/9/2017 12:43 PM, Hal Murray wrote:
>>> The other is a "real" GPS splitter such as the HP.Symmetricom 58535A or
>>> 58536A.  They usually have N connectors.  They usually include an amplifier
>>> so you don't see the 3 dB loss.  (They get power from the coax the same way
>>> the antenna does.)
>>>
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>

-- 
Stephen Tompsett

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Re: [time-nuts] Survey plot as art.

[Gary E. Miller]

Yo Tom!

On Mon, 9 Jan 2017 16:37:27 -0800
"Tom Van Baak"  wrote:

> Your ADEV plots differ from mine by orders of magnitude.

You are right, my ADEV plots are junk.  Removed.

It was the 24 hour scatter plots that I wanted you to look at.
Hard to argue with lat/lon data as reported by the device.

You can also checkout the TDOPs which are better on the MAX-M8N

> Remember
> this is time-nuts, not an NTP or a GPSD forum. The Adafruit GPS board
> is fine, even fantastic. But I suspect there are issues with your
> measurement techniques.

Hard for me to accept your relative opinion of two devices when you have
never played with one of them.  Whatever my techniques may be, I have
side-by-side concurrent data for many GPS.  Hopefully any systematic errors
cancel out in the comparisons.

And anyone can run, maybe even improve, the FOSS programs I'm using for
comparison as well.  

But I agree, moving off topic for time-nuts.

RGDS
GARY
---
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g...@rellim.com  Tel:+1 541 382 8588

Veritas liberabit vos. -- Quid est veritas?
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Re: [time-nuts] Survey plot as art.

[Tom Van Baak]

Hi Gary,

Your ADEV plots differ from mine by orders of magnitude. Remember this is 
time-nuts, not an NTP or a GPSD forum. The Adafruit GPS board is fine, even 
fantastic. But I suspect there are issues with your measurement techniques.

I'm happy to help, but let's take this off-list.

Thanks,
/tvb

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Re: [time-nuts] Survey plot as art.

[Bob kb8tq]

Hi


> On Jan 9, 2017, at 6:06 PM, Jay Grizzard  wrote:
> 
> Does anyone know of any schematics for amplified GPS splitters floating 
> around out there? I looked a while back and couldn't find anything. I use a 
> 58536A right now, but it's big and I hate having to have N to SMA cables.  It 
> would be awesome to be able to roll my own with all the connectors I want on 
> it…

The standard design is pretty simple:

1) DC bias coupler on the input
2) Protection on the input
3) Saw filter on the input (say -3 db)
4) Fairly normal (Mini Circuits) low noise amp with appropriate gain (say 12 to 
18 db)
5) two way splitter for the two banks of outputs (-3db)
6) two way splitter to each output (-3db) 
(obviously a 4 output device)
7) 3 db  (to 9 db) pads on each output
8) DC blocks on all but one output.
9) DC bias coupler on the one “magic” output. 

Some designs put a second filter after the amp. Some designs use ceramic 
filters rather than SAW’s.
Some designs go up to quite a few (like a dozen) outputs. Some have external 
power rather than
the bias pickoff / pass thru.

Bob

> 
> -j
> 
> On 1/9/2017 12:43 PM, Hal Murray wrote:
>> The other is a "real" GPS splitter such as the HP.Symmetricom 58535A or
>> 58536A.  They usually have N connectors.  They usually include an amplifier
>> so you don't see the 3 dB loss.  (They get power from the coax the same way
>> the antenna does.)
>> 
> 
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Re: [time-nuts] Survey plot as art.

[Jay Grizzard]

Does anyone know of any schematics for amplified GPS splitters floating 
around out there? I looked a while back and couldn't find anything. I 
use a 58536A right now, but it's big and I hate having to have N to SMA 
cables.  It would be awesome to be able to roll my own with all the 
connectors I want on it...


-j

On 1/9/2017 12:43 PM, Hal Murray wrote:

The other is a "real" GPS splitter such as the HP.Symmetricom 58535A or
58536A.  They usually have N connectors.  They usually include an amplifier
so you don't see the 3 dB loss.  (They get power from the coax the same way
the antenna does.)



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Re: [time-nuts] Survey plot as art.

[Gary E. Miller]

Yo Tom!

On Mon, 9 Jan 2017 14:01:18 -0800
"Tom Van Baak"  wrote:

> 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.

Yes, I also find the Adafruit wonderful.  It was my favorite GPS when I
got it.  I just find that the Uputronics GPS HAT is even better, for the
same price.

Compare these two pages, the first the Adafruit, the second an Uputronics
Version 2.  Sitting right next to each other, both iwth matching GPS
antennas.:

https://pi2.rellim.com/day/
https://pi4.rellim.com/day/

Especially check out the scatter plots.

The number of sats received, and the DOPs, are consistently better on
the Uputronics.

> Attached are ADEV MDEV TDEV plots of 5
> different GPS/1PPS receivers. The raw data is from:
> 
> http://www.leapsecond.com/pages/gpsdo-sim/

What?  No  pretty graphs?  :-)

> 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:

I find the Adafruit works better for me indoors with an external
antenna.  I find the uFL a pain for lab use.  The Uputronics have no
internal antenna and an SMA connector.  Plus it has a u-Blox 8.

But, to be fair, both are far beyond any practical needs I have.  YMMV.

RGDS
GARY
---
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
g...@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


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Re: [time-nuts] Survey plot as art.

[Tom Van Baak]

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

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Re: [time-nuts] Survey plot as art.

[Hal Murray]

g...@rellim.com said:
> 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. 

There are 2 options for splitters.  One is to use cable-TV splitters.  They 
probably have F connectors so you will need a kludge of adapters.

The other is a "real" GPS splitter such as the HP.Symmetricom 58535A or 
58536A.  They usually have N connectors.  They usually include an amplifier 
so you don't see the 3 dB loss.  (They get power from the coax the same way 
the antenna does.)

-- 
These are my opinions.  I hate spam.



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Re: [time-nuts] Survey plot as art.

[Björn Gabrielsson]

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


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Re: [time-nuts] Survey plot as art.

[Gary E. Miller]

Yo Björn!

On Mon, 9 Jan 2017 07:45:00 +0100
"Björn Gabrielsson"  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
---
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g...@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


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Re: [time-nuts] Survey plot as art.

[Björn Gabrielsson]

Hi Gary,

> Yo Artek!
>
> On Sun, 8 Jan 2017 17:18:06 -0500
> Artek Manuals  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

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Re: [time-nuts] Survey plot as art.

[Gary E. Miller]

Yo Hal!

On Sun, 08 Jan 2017 20:41:25 -0800
Hal Murray  wrote:

> g...@rellim.com said:
> >> The Adafruit receiver outputs NMEA format data.  The lat/lon values
> >> are sent as dddmm.mm format (ddd=degrees, mm.mm=minutes)  This
> >> restricts the resolution of the values. 
> 
> > Yes, easy to see the quantization in the Adafruit plot.  
> 
> Something doesn't look quite right.  If the problem was as simple as
> reduced lat/lon resolution, I'd expect the output to be on a grid.
> Instead, what I see is more like a grid that was also missing 1 out
> of N slots.  Where is that coming from?  How do I predict N?

Yes, the raw data shows that it is not using all the possible
precision.  It does skip lat/lons that are representable.

I'm almost at 45N, so that partlly explains why the lat missing codes
are smaller than the lon missing codes.

> I expect it's something like roundoff after the conversion from mm.mm
> to meters, or something like that.

No rounding happening in gpsd.  That is in the raw NMEA.

> Just to make sure we are on the same wavelength, this is the graph
> I'm looking at.
> 
> https://www.febo.com/pipermail/time-nuts/attachments/20170108/051ba89d/attachm
> ent-0003.png

Yup.

RGDS
GARY
---
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Re: [time-nuts] Survey plot as art.

[Hal Murray]

g...@rellim.com said:
>> The Adafruit receiver outputs NMEA format data.  The lat/lon values
>> are sent as dddmm.mm format (ddd=degrees, mm.mm=minutes)  This
>> restricts the resolution of the values.   

> Yes, easy to see the quantization in the Adafruit plot.

Something doesn't look quite right.  If the problem was as simple as reduced 
lat/lon resolution, I'd expect the output to be on a grid.  Instead, what I 
see is more like a grid that was also missing 1 out of N slots.  Where is 
that coming from?  How do I predict N?

I expect it's something like roundoff after the conversion from mm.mm to 
meters, or something like that.

Just to make sure we are on the same wavelength, this is the graph I'm 
looking at.

https://www.febo.com/pipermail/time-nuts/attachments/20170108/051ba89d/attachm
ent-0003.png


-- 
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Re: [time-nuts] Survey plot as art.

[Gary E. Miller]

Yo Mark!

On Mon, 9 Jan 2017 03:41:07 +
Mark Sims  wrote:

> The Adafruit receiver outputs NMEA format data.  The lat/lon values
> are sent as dddmm.mm format (ddd=degrees, mm.mm=minutes)  This
> restricts the resolution of the values.  Some receivers and newer
> NMEA specs support more digits past the decimal point.   Receivers
> that support native binary formats that report lat/lon as 32-bit
> floats show similar quantization.

Yes, easy to see the quantization in the Adafruit plot.

RGDS
GARY
---
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g...@rellim.com  Tel:+1 541 382 8588

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Re: [time-nuts] Survey plot as art.

[Sanjeev Gupta]

On Mon, Jan 9, 2017 at 5:52 AM, Gary E. Miller  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
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Re: [time-nuts] Survey plot as art.

[Gary E. Miller]

Yo Artek!

On Sun, 8 Jan 2017 17:18:06 -0500
Artek Manuals  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
g...@rellim.com  Tel:+1 541 382 8588

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Re: [time-nuts] Survey plot as art.

[Artek Manuals]

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

manu...@artekmanuals.com




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
---
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g...@rellim.com  Tel:+1 541 382 8588

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 "If you can’t measure it, you can’t improve it." - Lord Kelvin


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Re: [time-nuts] Survey plot as art.

[Gary E. Miller]

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
---
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g...@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


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Re: [time-nuts] Survey plot as art.

[Bob Camp]

Hi

There is a *lot* of difference between how various receiver architectures 
respond to multipath. 
You can spend hours of “quality time” looking into the various claims of people 
having completely 
eliminated muitipath by this or that software trick.

Bob

> On Jan 7, 2017, at 4:31 PM, Peter Reilley  wrote:
> 
> In my case (the original post) there can be no multipath difference, same 
> antenna and done at the same time.
> The length of the cables from the amplified splitter are about the same; 
> within inches.
> This must be some difference in the receiver, perhaps in the math?
> 
> Pete.
> 
> On 1/7/2017 4:16 PM, Bob Camp wrote:
>> Hi
>> 
>> In terms of multipath at GPS frequencies, a couple of inches is a *lot*. 
>> Also unless you have
>> pretty good antennas (as in much larger than 1” each) they will have phase 
>> issues unique
>> to each antenna. Phase cancellation and addition is what gives you multipath.
>> 
>> Bob
>> 
>>> On Jan 7, 2017, at 4:00 PM, Gary E. Miller  wrote:
>>> 
>>> Yo Bob!
>>> 
>>> On Sat, 7 Jan 2017 15:16:34 -0500
>>> Bob Camp  wrote:
>>> 
 The “simple” answer is that the weird legs going out from the central
 blob are the result of multi-path / reflections in the received
 signal. With enough data you might be able to correlate them to
 observed obstructions.
>>> I have lots of data from GPS with the antennas mounted 1 inch apart.
>>> They show different weird legs, so I suspect that local geology/architecture
>>> is not the whole story.
>>> 
>>> For example, compare the plot I just sent, to the one attached here.
>>> Two GPS right next to each other, very differently looking plots.
>>> 
>>> I'll admit to never generating plots over the same time interval,  I'll
>>> start a 24 hour test of two GPS right now.
>>> 
>>> RGDS
>>> GARY
>>> ---
>>> Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
>>> g...@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
>>> ___
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>>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>>> and follow the instructions there.
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Re: [time-nuts] Survey plot as art.

[Gary E. Miller]

Yo Hal!

On Sat, 07 Jan 2017 14:16:16 -0800
Hal Murray  wrote:

> g...@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
---
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g...@rellim.com  Tel:+1 541 382 8588

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Re: [time-nuts] Survey plot as art.

[Hal Murray]

g...@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.


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Re: [time-nuts] Survey plot as art.

[Peter Reilley]

The plots that I posted were of a 48 hour survey but only 32% of the 
survey had completed.


When the survey completes the plot display will disappear.

Pete.


On 1/7/2017 4:34 PM, Bryan _ wrote:

Thanks Pete, I have a Jupiter-T hooked up right now and wanted to see how the 
plot compares to your, unfortunately my antenna position is poor, so will be 
interesting. How many hours did you plot for?


-=Bryan=-



From: time-nuts <time-nuts-bounces+bpl521=outlook@febo.com> on behalf of Peter 
Reilley <preilley_...@comcast.net>
Sent: January 7, 2017 1:15 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Survey plot as art.

You start a precision survey with this command;
sp
You are offered 48 (hour) survey as an option.   I think that you can go
up to 96 hours.
During the survey the scatter plot is displayed.

Pete.



On 1/7/2017 3:32 PM, Bryan _ wrote:

How do you display the survey plot in LH? i.e. the keyboard commands


-=Bryan=-



From: time-nuts <time-nuts-boun...@febo.com> on behalf of Peter Reilley 
<preilley_...@comcast.net>
Sent: January 7, 2017 9:54 AM
To: Discussion of precise time and frequency measurement
Subject: [time-nuts] Survey plot as art.


This is the survey from my Trimble NTBW50AA.   It looks like some
bacteria floating around.

The curious thing are the excursions.   Rather than being noise like,
some follow a distinct
path.   But this is only over a few seconds so it seems unlikely that
they are caused by
weather conditions.   The survey from my Resolution T taken at the same
time and using
the same antenna (with a splitter) shows much less orderly excursions
and is more noise
like.


Trimble NTBW50AA survey.


Resolution T survey


Pete.

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Re: [time-nuts] Survey plot as art.

[Peter Reilley]

Another thought, perhaps the difference is between the quality of the 
oscillators.
The Resolution T has an ordinary XO while the NTBW50AA has an OCXO 
(possibly defective).
I would expect the XO to be noise like in a stable temperature 
environment.   The OCXO, if defective,
may have semi-controlled excursions from it's design frequency. However, 
I don't know
if the 10 MHz of the OXCO is used by the GPS chip and could therefore 
affect the calculated

position.

Pete.



On 1/7/2017 4:31 PM, Peter Reilley wrote:
In my case (the original post) there can be no multipath difference, 
same antenna and done at the same time.
The length of the cables from the amplified splitter are about the 
same; within inches.

This must be some difference in the receiver, perhaps in the math?

Pete.

On 1/7/2017 4:16 PM, Bob Camp wrote:

Hi

In terms of multipath at GPS frequencies, a couple of inches is a 
*lot*. Also unless you have
pretty good antennas (as in much larger than 1” each) they will have 
phase issues unique
to each antenna. Phase cancellation and addition is what gives you 
multipath.


Bob


On Jan 7, 2017, at 4:00 PM, Gary E. Miller  wrote:

Yo Bob!

On Sat, 7 Jan 2017 15:16:34 -0500
Bob Camp  wrote:


The “simple” answer is that the weird legs going out from the central
blob are the result of multi-path / reflections in the received
signal. With enough data you might be able to correlate them to
observed obstructions.

I have lots of data from GPS with the antennas mounted 1 inch apart.
They show different weird legs, so I suspect that local 
geology/architecture

is not the whole story.

For example, compare the plot I just sent, to the one attached here.
Two GPS right next to each other, very differently looking plots.

I'll admit to never generating plots over the same time interval,  I'll
start a 24 hour test of two GPS right now.

RGDS
GARY
--- 


Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
g...@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
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Re: [time-nuts] Survey plot as art.

[Gary E. Miller]

Yo Peter!

On Sat, 7 Jan 2017 16:31:25 -0500
Peter Reilley  wrote:

> 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.

RGDS
GARY
---
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
g...@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


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Re: [time-nuts] Survey plot as art.

[Bryan _]

Thanks Pete, I have a Jupiter-T hooked up right now and wanted to see how the 
plot compares to your, unfortunately my antenna position is poor, so will be 
interesting. How many hours did you plot for?


-=Bryan=-



From: time-nuts <time-nuts-bounces+bpl521=outlook@febo.com> on behalf of 
Peter Reilley <preilley_...@comcast.net>
Sent: January 7, 2017 1:15 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Survey plot as art.

You start a precision survey with this command;
sp
You are offered 48 (hour) survey as an option.   I think that you can go
up to 96 hours.
During the survey the scatter plot is displayed.

Pete.



On 1/7/2017 3:32 PM, Bryan _ wrote:
> How do you display the survey plot in LH? i.e. the keyboard commands
>
>
> -=Bryan=-
>
>
> 
> From: time-nuts <time-nuts-boun...@febo.com> on behalf of Peter Reilley 
> <preilley_...@comcast.net>
> Sent: January 7, 2017 9:54 AM
> To: Discussion of precise time and frequency measurement
> Subject: [time-nuts] Survey plot as art.
>
>
> This is the survey from my Trimble NTBW50AA.   It looks like some
> bacteria floating around.
>
> The curious thing are the excursions.   Rather than being noise like,
> some follow a distinct
> path.   But this is only over a few seconds so it seems unlikely that
> they are caused by
> weather conditions.   The survey from my Resolution T taken at the same
> time and using
> the same antenna (with a splitter) shows much less orderly excursions
> and is more noise
> like.
>
>
> Trimble NTBW50AA survey.
>
>
> Resolution T survey
>
>
> Pete.
>
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>
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Re: [time-nuts] Survey plot as art.

[Peter Reilley]

In my case (the original post) there can be no multipath difference, 
same antenna and done at the same time.
The length of the cables from the amplified splitter are about the same; 
within inches.

This must be some difference in the receiver, perhaps in the math?

Pete.

On 1/7/2017 4:16 PM, Bob Camp wrote:

Hi

In terms of multipath at GPS frequencies, a couple of inches is a *lot*. Also 
unless you have
pretty good antennas (as in much larger than 1” each) they will have phase 
issues unique
to each antenna. Phase cancellation and addition is what gives you multipath.

Bob


On Jan 7, 2017, at 4:00 PM, Gary E. Miller  wrote:

Yo Bob!

On Sat, 7 Jan 2017 15:16:34 -0500
Bob Camp  wrote:


The “simple” answer is that the weird legs going out from the central
blob are the result of multi-path / reflections in the received
signal. With enough data you might be able to correlate them to
observed obstructions.

I have lots of data from GPS with the antennas mounted 1 inch apart.
They show different weird legs, so I suspect that local geology/architecture
is not the whole story.

For example, compare the plot I just sent, to the one attached here.
Two GPS right next to each other, very differently looking plots.

I'll admit to never generating plots over the same time interval,  I'll
start a 24 hour test of two GPS right now.

RGDS
GARY
---
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
g...@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
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Re: [time-nuts] Survey plot as art.

[Gary E. Miller]

Yo Bob!

On Sat, 7 Jan 2017 16:16:44 -0500
Bob Camp  wrote:

> In terms of multipath at GPS frequencies, a couple of inches is a
> *lot*. Also unless you have pretty good antennas (as in much larger
> than 1” each) they will have phase issues unique to each antenna.
> Phase cancellation and addition is what gives you multipath.

I see up to 10x better/worse between GPS brands.  Measured by CEP().  A
much smaller change between antenna models.  I also have interchanged
antennas between my GPS to rule them out as the major contributing
source to error and discard the worst ones.

I just started 24 hour plots of 4 adjacent GPS.  I guess tomorrow I'll
rotate the antennas between GPS, witout moving the antennas, and repeat.

I suspect we may be just seeing different aspects of the same thing.  A
big difference between GPS models is probably the quality of multipath
rejection.  And I can easily change my GPS, but chaning my geoplogy is a
lot harder.

RGDS
GARY
---
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
g...@rellim.com  Tel:+1 541 382 8588

Veritas liberabit vos. -- Quid est veritas?
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Re: [time-nuts] Survey plot as art.

[Bob Camp]

Hi

In terms of multipath at GPS frequencies, a couple of inches is a *lot*. Also 
unless you have
pretty good antennas (as in much larger than 1” each) they will have phase 
issues unique
to each antenna. Phase cancellation and addition is what gives you multipath.

Bob

> On Jan 7, 2017, at 4:00 PM, Gary E. Miller  wrote:
> 
> Yo Bob!
> 
> On Sat, 7 Jan 2017 15:16:34 -0500
> Bob Camp  wrote:
> 
>> The “simple” answer is that the weird legs going out from the central
>> blob are the result of multi-path / reflections in the received
>> signal. With enough data you might be able to correlate them to
>> observed obstructions.
> 
> I have lots of data from GPS with the antennas mounted 1 inch apart.
> They show different weird legs, so I suspect that local geology/architecture
> is not the whole story.
> 
> For example, compare the plot I just sent, to the one attached here.
> Two GPS right next to each other, very differently looking plots.
> 
> I'll admit to never generating plots over the same time interval,  I'll
> start a 24 hour test of two GPS right now.
> 
> RGDS
> GARY
> ---
> Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
>   g...@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
> ___
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Re: [time-nuts] Survey plot as art.

[Peter Reilley]

You start a precision survey with this command;
sp
You are offered 48 (hour) survey as an option.   I think that you can go 
up to 96 hours.

During the survey the scatter plot is displayed.

Pete.



On 1/7/2017 3:32 PM, Bryan _ wrote:

How do you display the survey plot in LH? i.e. the keyboard commands


-=Bryan=-



From: time-nuts  on behalf of Peter Reilley 

Sent: January 7, 2017 9:54 AM
To: Discussion of precise time and frequency measurement
Subject: [time-nuts] Survey plot as art.


This is the survey from my Trimble NTBW50AA.   It looks like some
bacteria floating around.

The curious thing are the excursions.   Rather than being noise like,
some follow a distinct
path.   But this is only over a few seconds so it seems unlikely that
they are caused by
weather conditions.   The survey from my Resolution T taken at the same
time and using
the same antenna (with a splitter) shows much less orderly excursions
and is more noise
like.


Trimble NTBW50AA survey.


Resolution T survey


Pete.

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Re: [time-nuts] Survey plot as art.

[Gary E. Miller]

Yo Bob!

On Sat, 7 Jan 2017 15:16:34 -0500
Bob Camp  wrote:

> The “simple” answer is that the weird legs going out from the central
> blob are the result of multi-path / reflections in the received
> signal. With enough data you might be able to correlate them to
> observed obstructions.

I have lots of data from GPS with the antennas mounted 1 inch apart.
They show different weird legs, so I suspect that local geology/architecture
is not the whole story.

For example, compare the plot I just sent, to the one attached here.
Two GPS right next to each other, very differently looking plots.

I'll admit to never generating plots over the same time interval,  I'll
start a 24 hour test of two GPS right now.

RGDS
GARY
---
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
g...@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


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Re: [time-nuts] Survey plot as art.

[Bryan _]

How do you display the survey plot in LH? i.e. the keyboard commands


-=Bryan=-



From: time-nuts  on behalf of Peter Reilley 

Sent: January 7, 2017 9:54 AM
To: Discussion of precise time and frequency measurement
Subject: [time-nuts] Survey plot as art.


This is the survey from my Trimble NTBW50AA.   It looks like some
bacteria floating around.

The curious thing are the excursions.   Rather than being noise like,
some follow a distinct
path.   But this is only over a few seconds so it seems unlikely that
they are caused by
weather conditions.   The survey from my Resolution T taken at the same
time and using
the same antenna (with a splitter) shows much less orderly excursions
and is more noise
like.


Trimble NTBW50AA survey.


Resolution T survey


Pete.

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Re: [time-nuts] Survey plot as art.

[Bob Camp]

Hi

The “simple” answer is that the weird legs going out from the central blob are
the result of multi-path / reflections in the received signal. With enough data 
you
might be able to correlate them to observed obstructions. The simulation 
modeling 
required to make that happen might be a bit complex…..

Bob

> On Jan 7, 2017, at 3:07 PM, Gary E. Miller  wrote:
> 
> Yo Peter!
> 
> On Sat, 7 Jan 2017 12:54:45 -0500
> Peter Reilley  wrote:
> 
>> This is the survey from my Trimble NTBW50AA.   It looks like some 
>> bacteria floating around.
> 
> You can get those from any GPS using the program gpsprof from gpsd.
> 
> See attached for a 24 plot from a stationary GlobalSat MR-350P
> 
> I find these plots very useful when comparing GPS models.
> 
> RGDS
> GARY
> ---
> Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
>   g...@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
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Re: [time-nuts] Survey plot as art.

[Gary E. Miller]

Yo Peter!

On Sat, 7 Jan 2017 12:54:45 -0500
Peter Reilley  wrote:

> This is the survey from my Trimble NTBW50AA.   It looks like some 
> bacteria floating around.

You can get those from any GPS using the program gpsprof from gpsd.

See attached for a 24 plot from a stationary GlobalSat MR-350P

I find these plots very useful when comparing GPS models.

RGDS
GARY
---
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
g...@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


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Re: [time-nuts] Survey plot as art.

[Hal Murray]

preilley_...@comcast.net said:
> The curious thing are the excursions.   Rather than being noise like,  some
> follow a distinct path.   But this is only over a few seconds so it seems
> unlikely that  they are caused by weather conditions.   ...

I've seen similar quirks when a non-timing unit ran out of satellites.  I 
assume that it switched to dead reckoning mode and the last noisy sample 
included some velocity.  A few examples have made it to an orbit down near 
the south pole.

It would be interesting to look at the signal quality during and just before 
one of your little filaments.

-- 
These are my opinions.  I hate spam.



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Re: [time-nuts] Survey plot as art.

[Peter Reilley]

Try again;

Pete.


On 1/7/2017 12:54 PM, Peter Reilley wrote:


This is the survey from my Trimble NTBW50AA.   It looks like some 
bacteria floating around.


The curious thing are the excursions.   Rather than being noise like, 
some follow a distinct
path.   But this is only over a few seconds so it seems unlikely that 
they are caused by
weather conditions.   The survey from my Resolution T taken at the 
same time and using
the same antenna (with a splitter) shows much less orderly excursions 
and is more noise

like.


Trimble NTBW50AA survey.


Resolution T survey


Pete.

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