Garmin GPS-18 with prn 42 and 50, no DGPS.

Folks,
I am experiencing an odd problem with my GPS-18LVDS from Garmin and was
hoping for some insights.

First, I am located in Australia where at present according to my
GPS-18 we seem to be seeing two WAAS sats in nearly the same location.
These are reported as prn 42 and 50 and both have signal levels of 44-45.

Another GPS with the MTK chipset 'sees' only prn 50 and very smartly snap
into DGPS mode.

The Garmn on the other hand sees both 42 and 50 all the time and for only
about 1 minute approx 5 minutes after a cold boot displayed DGPS output
as expected. (See the GGA and RMC sentences) After that it never again
indicated DGPS fix.

I first updated the firmware in the GPS-18 which is why I went from a cold
boot. Apart from other obvious fixes this did alter the functionality wrt
the WAAS behaviour.

My first question is to Garmin, but that went off today and no replay as
yet.

But my question for now is why does the Garmin see two WAAS Sats at nearly
the same location? Are prn 42 and 50 that close or is the receiver
mistaken.

Are others in my part of the world with Garmin receivers also seeing the
effect?

Why is the MTK chipset in my secondary bluetooth GPS module able to deal
with these two sats when the market leader cannot?

Here is a slightly sanitised (location removed) NMEA dump and note that
this was collected hours after boot time in 3D mode.

$PGRMT,GPS 18LVC - software ver. 3.20,P,P,R,R,P,,22,R*34

$GPGLL,3404.0000,S,15100.0000,E,041719,A,A*51

$GPVTG,332,T,319,M,000.0,N,0000.0,K,A*1A

$PGRMV,0.0,-0.0,0.0*71

$PGRMF,426,274653,241007,041719,14,3404.0000,S,15100.0000,E,A,2,0,332,2,1*09
$PGRMB,,,,,,K,,,*2D
$PGRMM,WGS 84*06
$GPRMC,041720,A,3404.0000,S,15100.0000,E,000.0,331.8,241007,012.6,E,A*0B
$GPGGA,041720,3404.0000,S,15100.0000,E,1,07,1.2,134.6,M,19.1,M,,*53
$GPGSA,A,3,01,,11,14,,20,22,23,,31,,,2.0,1.2,1.6*31
$GPGSV,3,1,12,01,57,157,44,05,05,133,00,11,42,261,51,14,28,129,39*71
$GPGSV,3,2,12,19,04,323,00,20,24,231,50,22,18,072,44,23,15,282,39*7F
$GPGSV,3,3,12,30,10,119,00,31,70,069,46,42,49,342,45,50,50,350,44*70
$PGRME,5.4,M,6.6,M,8.5,M*22
$GPGLL,3404.0000,S,15100.0000,E,041720,A,A*5B


TIA
Doug
.

Relevant Pages

  • Re: Garmin GPS-18 with prn 42 and 50, no DGPS.
    ... You are seeing Japan's MSAS satellites. ... into DGPS mode. ... about 1 minute approx 5 minutes after a cold boot displayed DGPS output ... My first question is to Garmin, but that went off today and no replay as ...
    (sci.geo.satellite-nav)
  • Re: Differential GPS data adding noise.
    ... I have used a Garmin 23 DGPS beacon receiver (the old sub-AM band US Coast ... This is not possible with other retail GPS units. ... >>the Differential GPS correction data the data from the device is more ...
    (sci.geo.satellite-nav)
  • Re: Garmin GPS-18 with prn 42 and 50, no DGPS.
    ... I thought the DGPS came for free if the WAAS signal was available. ... I am evaluating the Garmin unit and right now it seems the unit might have ... due to the 5Hz data rate or the DGPS fixes. ... Absolute position is not as important to me as dynamic performance, ...
    (sci.geo.satellite-nav)
  • Re: Combination Cables
    ... > You won't get a premade cable, at least not from Garmin.. ... > If you have lost the GBR 21 cable, ... with DGPS, seeing how far I can receive a station, etc. ... Earl Needham ...
    (sci.geo.satellite-nav)