Garmin GPS 72 and WAAS/EGNOS

[shilcor]

Hi All,
After last week's announcement that EGNOS had gone live I dug out my Garmin GPS72 and enabled WAAS thinking that it might be able to take advantage of EGNOS. Although I could pick up 8 satellites, none of them indicated that a differential signal was being received (which indicates that WAAS is working according to the manual). I flashed it with the latest May 2008 firmware but that made no difference. I was under the impression that any WAAS capable receiver should be able to take advantage of EGNOS - am I wrong there ?

[dales]

I'd really like to hear from someone who can explain this authoritatively.

In the meantime, a browse through the EGNOS site reveals this list of EGNOS compatible receivers (if you follow the link to the pdf file). The list includes the GPS72 and my own Vista.

If I understand correctly what's said in the EGNOS site, then yes you are right that WAAS and EGNOS are compatible. However last time I tried the WAAS out (a few years ago) it worked fine but the satellite(s) were very low in the SSW sky so you needed to point your receiver that way from high ground to get reception. It also took 10mins+ to lock on.

I don't know the orientation of the EGNOS satellites. The website quotes their E/W locations, but I didn't spot their N/S locations.

Dales.

[AllyCat]

Hi,

First, you must not only enable WAAS/EGNOS on most Garmin handhelds, you must also disable "Battery Saver" mode. So, since more data processing is involved as well, EGNOS may impact considerably on the battery running time of your GPS.

The EGNOS satellites are geostationary so they must be located above the equator giving an elevation in the UK of about 20 degrees above the horizon (rather less in the north). EGNOS #37 (PRN 124) is located between Astra 1 (the old Sky analogue) and Astra 2 (Sky digital) so you should be able to receive EGNOS almost wherever a Sky dish works (but you may have to climb up a ladder).

Bear in mind that the EGNOS satellites do not transmit range (position) data, but only corrections for "regional" errors (mainly atmospheric effects) to at best improve the position by a few metres. Thus, if you already have a position accurate to say 5 metres, then EGNOS might improve the accuaracy by a couple of metres. But if your current position is only accurate to say 20m due to "local" effects such as poor satellite geometry (or a restricted view of the sky) or signals bounced off buildings, etc., then EGNOS will give no practical benefit.

Anyway, I gave my GPS76 a try this morning (from an upstairs window here in London) and it quickly reported signals from satellites 33 (SW) and 37 (SE) but it was many minutes before the 'D's finally appeared on the signal bars for the other satellites. Note that the GPS may also find other EGNOS/WAAS satellites, but these signals are of no use because they do not carry the correction data for the UK region.

Cheers, Alan.
_________________
Garmin GPS72H/76/60/45, Etrex H, Mapsource v6.5.
Acer N50,HP114,Loox N560,Dell x50,CF/SD cards to 4/32GB.
RoyalTek,Holux236,Navman B10 & Copilot(Globalsat) BT GPS,TomTom5/6.
Memory Map (v5.4.2 & v5.1.3 OS & Euro), GPS gate,OSGPSconverter.

[peter_tesar]

Hello AllyCat,
I have found your post from Oct 09, 2009 3:46 pm, you are mentioning your Garmin GPS76 unit. I have this unit too, from cca. 2005 and now I have problems with WAAS/EGNOS with it.
I early years 2006-2007 I regularly used WAAS/EGNOS function (my location is Central Europe), the "D" letters were appearing after few minutes of reception. My indicated accuracy was (with good satellite constellation) about 1.2-1.5 m.
Then I didn't used my unit.
Now I need it again, but I am not able to get the WAAS/EGNOS functionality. I tried it several times, I always waited more than an hour, but without success, the "D" letters didn't appeared. I see two EGNOS satellites with good signal. Indicated accuracies are now about 4 m. I suspect that the problem is that now there are more then one EGNOS satellite and the unit is confused and is not able to work in this situation.
I sent a query to Garmin, they recommended me to reinstall the firmware (although I have already the only one available firmware 2.20) or master reset the unit (I will lose all my waypoints and tracks). I have not tried it yet, but until I lose all my data, i would like to know if the GPS76 is potentially able to work now in Europe with more EGNOS satellites in the sky.
Unfortunately i do not know any other GPS76 user. Can I ask you to help with this? Is EGNOS now working in your unit? Are you receive more than one EGNOS satellite?
Thank you.
Peter Tesar.

[AllyCat]

Hi Peter,

Sorry for my late reply. As I described above, I'm not enthusiastic about the benefits of WAAS/EGNOS (for "amateur" applications) and rarely try to use it. Also, I "replaced" my GPS76 with a 72H because of the much higher sensitivity of the newer models (in other respects the 72H is a disappointment).

However, I do still have the GPS76 so charged up the batteries and ran it "side by side" with the 72H in WAAS/EGNOS mode here in London. The 72H started in Differential mode fairly quickly, but the GPS76 took a considerable time to acquire any position at all (it had to do a full "search the sky" cold start). However, after moving it around a few times to point in the "best" direction, the "D"s did eventually appear on the signal strength screen. Signal strengths for satellite numbers 33 and 39 were shown, but only 39 appears to be used (here in the UK).

So, it does seem that this rather old unit is still fundamentally able to receive WAAS/EGNOS signals in the UK, although I still doubt its practical usefulness.

Cheers, Alan.
_________________
Garmin GPS72H/76/60/45, Etrex H, Mapsource v6.5.
Acer N50,HP114,Loox N560,Dell x50,CF/SD cards to 4/32GB.
RoyalTek,Holux236,Navman B10 & Copilot(Globalsat) BT GPS,TomTom5/6.
Memory Map (v5.4.2 & v5.1.3 OS & Euro), GPS gate,OSGPSconverter.

[peter_tesar]

Hello Alan,
thanks for reply.
I am surprised that you have upgraded from 76 to 72. When I planned to buy a GPS, I was choosing between these two models and 72 was cheaper version of 76 with lower display resolution. Maybe 72H is something better.

Thank you that you have checked GPS76 with Egnos.

I did some test in past days as well. I forced the unit to find different EGNOS satellites (I started the unit indoors and when the it didn't find any signals, it asked for a new position, I set manually a false position somewhere in Canada or Russia). Then the unit found other EGNOS satellites, either pair No. 33+37 or 37+39. Fortunately yesterday satellite No. 37/PRN124 was not transmitting, it was completely without signal and I had signal solely either from 33 or 39, both with good reception.

When I received No. 33, I had no "D" on screen after a hour of reception. When 39 was received, "D"s appeared on two or three satellite bars, the fix was "2D Differential", but the accuracy was worse than without WAAS.
So now it is clear that the unit is fundamentally still able to work with EGNOS, but it is confused and is not able to work with EGNOS in full extent. A new firmware would be highly needed, but I am afraid that it will be never released.

You are writing that "...but only 39 appears to be used...". I would like to ask you, how do you knew which particular EGNOS satellite is used? From color of signal bar? My experience from year 2006, when EGNOS worked for me as expected ("D"s were on all GPS satellites and the fix was 3D Differential) is that the signal bar for EGNOS satellite was always only grey, I have never seen it black (as normal GPS satellites when they are used for calculation). Your EGNOS signal turns to black?

Did you have recently "D"s on all satellite bars or only on some of them?

Thank you for consultancy.

Peter.

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