etrex 30 : GPS + GLONASS

I found this report on the etrex 20 (same as etrex 30 other than some
missing features (baro/compass)).

This screen shot:
http://gpstracklog.com/wp-content/uploads/2011/10/GLONASS-on-eTrex_thumb.jpg

Shows that it appears to be (at least) a 12-GPS-channels and 12-GLONASS
channel unit.

As shown it's got 12 GPS "in view" and 11 GLONASS "in view" while
tracking 9 GPS and 6 GLONASS sats (total 15). No WAAS sats in the GPS
line ... maybe tracked on another channel, not listed?

The "error" calc (9 ft) seems optimistic since the best contributors to
horizontal accuracy were not being tracked (esp. to the north) and there
is no sure indication of WAAS tracking at the time either.

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wrote:
S-on-eTrex_th...

Appears to use the NMEA convention for numbering satellites:

a) GPS satellites are identified by their PRN numbers, which range
from 1 to 32.

b) The WAAS system has reserved numbers 33 =96 64 to identify its
satellites.

c) The numbers 65 =96 96 are reserved for GLONASS satellites. GLONASS
satellites are identified by 64+ satellite
slot numbers. The slot numbers are 1 through 24 for the full GLONASS
constellation of 24 satellites, thus giving a
range of 65 through 88. The numbers 89 through 96 are available if
slot numbers above 24 are allocated to on-orbit
spares.

--- CHAS

On 2011-10-27 17:09 , HIPAR wrote:
NASS-on-eTrex_th...
S

Sure - like I said - no WAAS on that display. But that doesn't mean WAAS =

wasn't being tracked.


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Sure - like I said - no WAAS on that display. But that doesn't mean
WAAS wasn't being tracked.

On my Etrex Vista HCx, I dimly recall that the default was to disable
WAAS. Once enabled, I see "PRN" 48 or 51 and D in many of the
satellites. This receiver is obviously in default mode because the
first thing anyone would do is set it to metric :-)

One has to wonder how the combined GPS/GLONASS solution is done in the
presence of WAAS, in terms of the GPS+D vs GLONASS a priori error
estimates. This is arguably a similar situation to GPS vs GPS+D, but it
seems likely to have eg 8 GPS+D and 6 Glonass over long periods of time.


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On 2011-10-27 19:58 , Greg Troxel wrote:

Only in the real world. Americans have metric paralysis unless they
were in the military or have a general science education.

Note that the _primary_ system of weights and measures in the US _is_
the metric system since the 1890's. Unfortunately, due to a lot of
trade with Britain, the US put an exception clause in the law.


You'd get mostly WAAS'd GPS + un-SBAS'd GLONASS in the solution. A
clever algorithm might, post acquisition, kick out the GLONASS from the
solution so that it doesn't pollute it.

IAC, I know several ground truth points that are easy to identify and
that register well on Google Earth - I'll be testing the etrex 30 at
those points when I get it.

Note that in Europe the EGNOS signal covers GLONASS as well as GPS, so
performance there could be even better than in N.A. (Speculative).

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