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RINEX on Garmin GPSMAP 66sr


Pete_the_Geek

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I have an interesting issue on my 66sr.

 

I have been doing a lot of learning/playing with RINEX observations and believe I have have come across an issue where RINEX appears to receive multi GNSS Multi-Band RINEX data initially  but after somewhere around 6 hours, GLONASS satellites (G1 and G2) begin to reduce until they are no longer received and similarly for Galileo (E1 and E5)  but after 10 hours approximately but these times vary.

The handheld never recovers so only GPS L1 and L5 is received from that point on. L5 also begins to reduce but is still received sporadically.

 

Before you ask, I have done several tests all with the same result, with my main test site being in a very clear view of the sky with no obstructions 10 degrees above horizontal. Also it is very near (12km) from a UK base station that continues to receive multi frequency GPS, Galileo, GLONASS and BeiDou signals then the 66sr does not.

 

Has anyone else had this experience?

 

I have raised a support case and am running another test occasionally viewing which satellites the device's satellites status shows it can see,  comparing this to my phone at the same time so I can further determine if it is a RINEX issue or a device issue. 

grmn269p33_all_visibility.png

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After having found RINEX files of my 66sr dating from August 2021, a month after its purchase, so firmware version 3.30, the Galileo satellites were flashing all the time and I was convinced that they were not taken into account in the precision du 66sr, well I made a mistake thanks to the RINEX files which prove that the Galileo satellites despite the blinking were indeed active.

See image below:

ALL Satellites and L5 satellites.

 

ALL-23-08-2021r.jpg

L5-23-08-2021r.jpg

Edited by mimichris
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mimichris: Can you please share the "SYS / # / OBS TYPES " lines from one of the 66sr RINEX observation (obs) files?

 

In fact, could you copy and paste the header section of a 66sr OBS file? (The header is the top of the file, with "END OF HEADER" and a blank line at the end of the section.)

 

Many thanks!

 

Attached is a sample header from a u-blox ZED-F9P for reference.

Sample RINEX observation file header.png

Edited by ObeliskAG
Clarification
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    3.04           OBSERVATION DATA    M (MIXED)           RINEX VERSION / TYPE
RINEXWRITER         GARMIN              20211125 125336 UTC PGM / RUN BY / DATE
Download navigation file using this link:                   COMMENT
ftp://cddis.gsfc.nasa.gov/gnss/data/daily/2021/329/21p/     COMMENT
BRDC00IGS_R_20213290000_01D_MN.rnx.gz                       COMMENT
GARMIN MARKER                                               MARKER NAME
                                                            MARKER NUMBER
                                                            MARKER TYPE
                                                            OBSERVER / AGENCY
GPSMAP 66sr 4.90                                            REC # / TYPE / VERS
                                                            ANT # / TYPE
  4625390.0000   271704.1562  4368683.0000                  APPROX POSITION XYZ
        0.0000        0.0000        0.0000                  ANTENNA: DELTA H/E/N
G    8 C1C L1C D1C S1C C5X L5X D5X S5X                      SYS / # / OBS TYPES
R    4 C1C L1C D1C S1C                                      SYS / # / OBS TYPES
E    8 C1Z L1Z D1Z S1Z C5X L5X D5X S5X                      SYS / # / OBS TYPES
C    4 C1X L1X D1X S1X                                      SYS / # / OBS TYPES
J    8 C1C L1C D1C S1C C5X L5X D5X S5X                      SYS / # / OBS TYPES
I    4 C5A L5A D5A S5A                                      SYS / # / OBS TYPES
  2021    11    25    12    53   36.000000                  TIME OF FIRST OBS
G                                                           SYS / PHASE SHIFT   
R                                                           SYS / PHASE SHIFT   
E                                                           SYS / PHASE SHIFT   
C                                                           SYS / PHASE SHIFT   
J                                                           SYS / PHASE SHIFT   
I                                                           SYS / PHASE SHIFT   
  0                                                         GLONASS SLOT / FRQ #
 C1C    0.000 C1P    0.000 C2C    0.000 C2P    0.000        GLONASS COD/PHS/BIS 
                                                            END OF HEADER

Edited by mimichris
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L'entête du 66sr version 3.80 quand Galileo clignotait sans arrêt :

     3.04           OBSERVATION DATA    M (MIXED)           RINEX VERSION / TYPE
RINEXWRITER         GARMIN              20210801 070212 UTC PGM / RUN BY / DATE
Download navigation file using this link:                   COMMENT
ftp://cddis.gsfc.nasa.gov/gnss/data/daily/2021/213/21p/     COMMENT
BRDC00IGS_R_20212130000_01D_MN.rnx.gz                       COMMENT
GARMIN MARKER                                               MARKER NAME
                                                            MARKER NUMBER
                                                            MARKER TYPE
                                                            OBSERVER / AGENCY
GPSMAP 66sr 3.80                                            REC # / TYPE / VERS
                                                            ANT # / TYPE
  4625390.0000   271702.4688  4368679.0000                  APPROX POSITION XYZ
        0.0000        0.0000        0.0000                  ANTENNA: DELTA H/E/N
G    8 C1C L1C D1C S1C C5X L5X D5X S5X                      SYS / # / OBS TYPES
R    4 C1C L1C D1C S1C                                      SYS / # / OBS TYPES
E    8 C1Z L1Z D1Z S1Z C5X L5X D5X S5X                      SYS / # / OBS TYPES
C    4 C1X L1X D1X S1X                                      SYS / # / OBS TYPES
J    8 C1C L1C D1C S1C C5X L5X D5X S5X                      SYS / # / OBS TYPES
I    4 C5A L5A D5A S5A                                      SYS / # / OBS TYPES
  2021     8     1     7     2   12.000000                  TIME OF FIRST OBS
G                                                           SYS / PHASE SHIFT   
R                                                           SYS / PHASE SHIFT   
E                                                           SYS / PHASE SHIFT   
C                                                           SYS / PHASE SHIFT   
J                                                           SYS / PHASE SHIFT   
I                                                           SYS / PHASE SHIFT   
  0                                                         GLONASS SLOT / FRQ #
 C1C    0.000 C1P    0.000 C2C    0.000 C2P    0.000        GLONASS COD/PHS/BIS 
                                                            END OF HEADER

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On 9/28/2021 at 8:54 PM, Pete_the_Geek said:

I have an interesting issue on my 66sr.

 

I have been doing a lot of learning/playing with RINEX observations and believe I have have come across an issue where RINEX appears to receive multi GNSS Multi-Band RINEX data initially  but after somewhere around 6 hours, GLONASS satellites (G1 and G2) begin to reduce until they are no longer received and similarly for Galileo (E1 and E5)  but after 10 hours approximately but these times vary.

The handheld never recovers so only GPS L1 and L5 is received from that point on. L5 also begins to reduce but is still received sporadically.

 

Before you ask, I have done several tests all with the same result, with my main test site being in a very clear view of the sky with no obstructions 10 degrees above horizontal. Also it is very near (12km) from a UK base station that continues to receive multi frequency GPS, Galileo, GLONASS and BeiDou signals then the 66sr does not.

 

Has anyone else had this experience?

 

I have raised a support case and am running another test occasionally viewing which satellites the device's satellites status shows it can see,  comparing this to my phone at the same time so I can further determine if it is a RINEX issue or a device issue. 

grmn269p33_all_visibility.png

After this test, did you try to turn off the 66sr and then turn it on again to see if the lost satellites returned normally?

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On 11/26/2021 at 2:26 AM, mimichris said:

G    8 C1C L1C D1C S1C C5X L5X D5X S5X                      SYS / # / OBS TYPES

 

R    4 C1C L1C D1C S1C                                      SYS / # / OBS TYPES
E    8 C1Z L1Z D1Z S1Z C5X L5X D5X S5X                      SYS / # / OBS TYPES
C    4 C1X L1X D1X S1X                                      SYS / # / OBS TYPES
J    8 C1C L1C D1C S1C C5X L5X D5X S5X                      SYS / # / OBS TYPES
I    4 C5A L5A D5A S5A                                      SYS / # / OBS TYPES

 

mimichris: Thanks for posting this.

 

For anyone else that cares, a more readable decoding of the above observation types:

GPS: 8 observation types- L1: Code, Phase, Doppler, Raw. L5: Code, Phase, Doppler, Raw
GLONASS: 4 observation types, L1: Code, Phase, Doppler, Raw
Galileo: 8 observation types - L1: Code, Phase, Doppler, Raw. L5: Code, Phase, Doppler, Raw
BDS: 4 observation types, L1: Code, Phase, Doppler, Raw
QZSS (Japan coverage): 8 observation types - L1: Code, Phase, Doppler, Raw. L5: Code, Phase, Doppler, Raw
NavIC/IRNSS (India coverage): 4 observation types, L5: Code, Phase, Doppler, Raw

 

The above is a curious list. The "good" news:

- It looks like the RINEX file contains carrier phase data, which is very useful for precision post processing

- Good multi-frequency (L1/L5) coverage of GPS and Galileo (QZSS is not global coverage)

- With a RINEX file we don't have to worry about some proprietary, receiver specific, binary file to be compatible with RTKLIB and other tools

 

The "bad" news:

- Only single-frequency observations for each: GLONASS, BDS, NavIC

- At this time, I'm not aware of any post-processing services, such as CSRS-PPP, that support processing L5 data. (Maybe some do? I only have L1 and L2 data to test with.)

- There do not appear to be SBAS observations in the RINEX file, which probably isn't such a big deal for an L5 equipped receiver

 

Perhaps someone can comment on the achievable precision with post-processing GPSMAP 66sr RINEX files?

Edited by ObeliskAG
Clarity
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1 hour ago, ObeliskAG said:

- There do not appear to be SBAS observations in the RINEX file, which probably isn't such a big deal for an L5 equipped receiver

 

Correct.

 

Garmin Multi-Band GPSr do not employ traditional SBAS (WAAS/EGNOS) as they are able to make live correction calculations using the L1/L5 data available to them.

 

Or so I am told....

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48 minutes ago, Atlas Cached said:

 

Correct.

 

Garmin Multi-Band GPSr do not employ traditional SBAS (WAAS/EGNOS) as they are able to make live correction calculations using the L1/L5 data available to them.

 

Or so I am told....

 

My understanding is that all multi-frequency receivers should be able to perform ionospheric delay corrections - which is only one of the things that SBAS provides. However, I think the majority of them still will utilize SBAS signals. For example, this  Trimble R12i is their highest end, 672 channel, survey grade, GNSS receiver (probably >US$20K) and it receives SBAS signals. This Ardusimple simpleRTK2Blite kit is the most cost-effective mutli-frequency GNSS I am aware of, and it also receives SBAS. So it is a bit surprising that the Garmin 66sr doesn't support SBAS. I really do wonder what receiver they are using... gpsrchive.com doesn't seem to have this information :(

Edited by ObeliskAG
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Glonass is only in single frequency L1. Maybe one day.....
I notice that few GPS satellites are L5, I don't know if all the GPS satellites are equipped to have the L5, but it is little compared to Galileo whose all the satellites are L5, it must be them which give the best precision from 66sr.

There is no SBAS on the Garmin 65s and 66sr multi-band, but the Sony chips used according to (according to information from the web) this website (https://www.sony.com/en / SonyInfo / News / Press / 202008 / 20-069E /) used behaves after it is an internal firmware setting and 66sr.

With older firmware versions 3.80 and lower, Galileo satellites still flashed even after several hours of operation, but that did not prevent them from being factored into the accuracy of the 66sr (see RINEX file).

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11 hours ago, mimichris said:

There is no SBAS on the Garmin 65s and 66sr multi-band, but the Sony chips used according to (according to information from the web) this website (https://www.sony.com/en / SonyInfo / News / Press / 202008 / 20-069E /)

 

There have been no confirmation that these are the chips used in the Garmin Multi-Band devices, nor does that website confirm anything.

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14 hours ago, mimichris said:

Glonass is only in single frequency L1. Maybe one day.....
I notice that few GPS satellites are L5, I don't know if all the GPS satellites are equipped to have the L5, but it is little compared to Galileo whose all the satellites are L5, it must be them which give the best precision from 66sr.

There is no SBAS on the Garmin 65s and 66sr multi-band, but the Sony chips used according to (according to information from the web) this website (https://www.sony.com/en / SonyInfo / News / Press / 202008 / 20-069E /) used behaves after it is an internal firmware setting and 66sr.

With older firmware versions 3.80 and lower, Galileo satellites still flashed even after several hours of operation, but that did not prevent them from being factored into the accuracy of the 66sr (see RINEX file).

 

GLONASS provides L1, L2 and L3 frequencies, just not L5 until the GLONASS-KM satellites come to be.

 

It was a while before there were enough GPS satellites to activate L2C messages. It looks like currently 16 GPS satellites are providing L5 signals with 24 satellites planned to be available by 2027. Exciting times!

 

The Sony CXD5610GF receiver can be had for US$9!?! It's thrilling to see the price of multi-frequency receivers coming down. A u-blox ZED-F9P is US$139 - $199 each, depending on quantity. It is possible that Garmin 66sr could be using a Broadcom BCM47755 receiver chip. (I've owned a Trimble 4000SSi and Trimble Geo XH, and even very old and used, these were expensive receivers - not to mention Trimbles attitude about software and protocols :mad: For example, other than pure greed, why does Trimble sell devices like Geo XH without pre-installing TerraSync on them? Companies like Trimble are the reason the open source / open standards /right-to-repair communities get out of bed in the morning. Not that Garmin is an example of a good citizen.)

 

SBAS is beneficial in that in addition to providing ionospheric correction data (that may not be as good as a multi-frequency receiver can determine on its own), it can provide status and integrity data to increases confidence in the system(s).

 

Either way, I think the Garmin 66sr is the first consumer GNSS handheld receiver that is multi-frequency, which is a very exciting development - too bad they don't have any competition. (I think the Xiaomi Mi 8 smartphone might have been the first device, but the Garmin likely has a higher-performing antenna, which is significant.) I wonder if Trimble, Javad, Leica, NovaTel, etc. are considering the long-term ramifications of all this? There could be a revolution in GIS, especially in the developing world.

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It is certainly not the Broadcom chip which is on the 66sr, I had read on a website that it was the Sony chip mentioned above but I did not have the confirmation,
Garmin does not give the source of its components, it seems that Garmin chooses and sorts the best satellites on these multi-band GPS because I should have more satellites including the Galileo, on my MI9 smartphone, I have at least 25 to 30 satellites taken into account, including a certain number of L5s.
There will soon be two more Galileo satellites that were sent into space on December 2nd.

Still, the trace recorded with a 66sr is not much better than the ones I recorded on my old non-multiband 66s. I sometimes have significant deviations from the path or the road on which I am, without any trees and with a completely clear sky.

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10 hours ago, mimichris said:

It is certainly not the Broadcom chip which is on the 66sr, I had read on a website that it was the Sony chip mentioned above but I did not have the confirmation,
Garmin does not give the source of its components, it seems that Garmin chooses and sorts the best satellites on these multi-band GPS because I should have more satellites including the Galileo, on my MI9 smartphone, I have at least 25 to 30 satellites taken into account, including a certain number of L5s.
There will soon be two more Galileo satellites that were sent into space on December 2nd.

Still, the trace recorded with a 66sr is not much better than the ones I recorded on my old non-multiband 66s. I sometimes have significant deviations from the path or the road on which I am, without any trees and with a completely clear sky.

 

A GNSS receiver can by configured to filter satellites by their elevation above the horizon, as lower elevations can provide poor data. Enabling RAIM and SBAS functionality may also preclude specific satellites from use. It could be that the Garmin receiver is being more selective of signal quality/integrity than a MI9 smartphone.

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1 hour ago, ObeliskAG said:

 

A GNSS receiver can by configured to filter satellites by their elevation above the horizon, as lower elevations can provide poor data. Enabling RAIM and SBAS functionality may also preclude specific satellites from use. It could be that the Garmin receiver is being more selective of signal quality/integrity than a MI9 smartphone.

 

Exactly. The GPSr does not need all 90 satellites available in the sky, just the few that provide the best plotting solution.

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GPSMAP 66sr Firmware Update 5.70 released 10FEB23:

Changes made from version 5.50 to 5.70:
 

  • Fixed possible issue when attempting to navigate courses.
  • Fixed possible issue with searching for waypoints near a city.
  • Fixed missing/expired CPE status using Wi-Fi.
  • Fixed potential issues with acquiring a GPS fix using Multi-GNSS.
  • Fixed possible shutdown when saving activities from the map page.
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