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Old 17th Feb 2012, 17:12   #1 (permalink)
 
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Aera 500/EGNOS

Similar to another thread, could I just check I've understood this properly...?

1. WAAS is the same thing as Differential GPS.

2. The AERA 500 can get DGPS/WAAS and when active, the status page shows 3D Differential or 2D Differential.

3. EGNOS is the same as WAAS so a receiver which can get one can get the other.

If so, why does my Aera not appear to get EGNOS reception?

Tim
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Old 17th Feb 2012, 17:39   #2 (permalink)
 
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WAAS is not the same as DGPS; WAAS is enhanced stand-alone GPS (basically it uses a lot of research data to minimise GPS errors), DGPS uses comparison to a (relatively) nearby GPS receiver in a known position. Both enhance position, WAAS less so, but doesn't require a second fixed groundstation.

The AERA 500 does WAAS, but not DGPS.

WAAS is a US solution to enhanced GPS, EGNOS is a European solution to enhanced GPS. They work in similar but not quite identical manners.

So far as I know the AERA 500 does not have EGNOS capability.

WAAS+DGPS would give fantastic accuracy. But, you need some fairly specialised kit to do that.

G
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Old 17th Feb 2012, 20:37   #3 (permalink)
 
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Ah. Thanks. So when the Aera reports '3D Differential' (which the user manual assures me that it can) it is receiving WAAS not DGPS.

Less confused now, thanks!

That also explains why my old Lowrance Airmap 1000 never got WAAS either, if it doesn't work in Europe.

Tim

PS Hang on, though, What is SBAS? | EGNOS Portal says WAAS and EGNOS are interoperable and a receiver which can get one can get the other; and Receiver list | EGNOS Portal lists the Aera series as compliant. Confused again...
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Old 18th Feb 2012, 10:57   #4 (permalink)
 
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Quote:
PS Hang on, though, What is SBAS? | EGNOS Portal says WAAS and EGNOS are interoperable and a receiver which can get one can get the other; and Receiver list | EGNOS Portal lists the Aera series as compliant. Confused again...
That's correct. WAAS capable devices can take advantage of EGNOS. If your Garmin shows 3D Differential, it makes use of EGNOS. You can check the satellites it tracks, the ones with numbers 33-51 are the EGNOS satellites. There are a few geostationary satellites that receive correction data from ground stations in the UK and France (+ Spain for Artemis) and broadcast it on the same frequency as the standard GPS satellites.

Differential GPS (DGPS) was previously used (only in the US I think) and it consists of fixed ground stations that know their exact position and determine their GPS position. The difference is then encoded in a long wave (LW) signal that travels over the ground and can be received by other stations to improve their position fix. The idea was to install such ground stations in the vicinity of aerodromes but having a few space vehicles providing more generic correction information gets us to ILS accuracy as well and is of course much more convenient.

Last edited by achimha; 18th Feb 2012 at 11:27.
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Old 18th Feb 2012, 16:55   #5 (permalink)
 
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Looking again at the manual, it actually states that it will show '3D Differential' if DGPS is being received. The example satellite status window shows satellite 51 is being received. So I wonder if WAAS/EGNOS is only shown by a satellite number over 32? Though if so I didn't know it could get DGPS.

Tim
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Old 18th Feb 2012, 18:39   #6 (permalink)
 
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There is a separate ground based DGPS system active in the UK, transmitting at around 300kHz. Its designed for shipping but I don't see why aircraft wouldn't be able to pick it up (since we can pick up NDBs on similar frequencies). It probably would need an additional aerial though.
Satellite Navigation

However the Garmin website only mentions SBAS / WAAS for Aera 500. Perhaps it is picking up the EGNOS signal but doesn't know what to call it - so it is defaulting to calling it "DGPS" instead? The WAAS satellite signal isn't likely to reach Europe.

My understanding is that all of the satellite based augmentation systems (SBAS) WAAS, EGNOS, MSAS, GAGAN (when it goes live) are all compatible with each other. So if you see DGPS on your Aera while in Europe it will be using EGNOS.
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Old 19th Feb 2012, 00:07   #7 (permalink)
 
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I'm not totally convinced about this. If you look on the Garmin website, the data sheet for the Aera 500 shows WAAS capability. EGNOS is not mentioned.

Searching on Garmin's website, some of the very high end units show WAAS/EGNOS, but none of the lower end units show dual capability. I find it hard to believe that if the lower end units like the Aera had EGNOS as well as WAAS capability, Garmin wouldn't ensure that was listed on their various brochures and spec sheets.

(Turning on my own Aera 500, sat here in Buckinghamshire, it also doesn't show any satellite numbers above 31).

G
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Old 19th Feb 2012, 00:45   #8 (permalink)
 
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Garmin panel mounted equipment is EGNOS compliant: See here. EGNOS is satellite based.
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Old 19th Feb 2012, 07:40   #9 (permalink)
 
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Genghis,

Hmm. The cynic in me fears you may be right, but this link:

Receiver list | EGNOS Portal

does include the Aera series (as this is a chipset issue I doubt it's any different with the higher Aera models), albeit with no guarantees.

I'll have to keep an eye on mine. Certainly I've never seen it report Differential.

Tim
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Old 19th Feb 2012, 09:30   #10 (permalink)
 
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My 295 had EGNOS capability, but when I "upgraded" to the Aera 500, I lost that feature.
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Old 19th Feb 2012, 09:30   #11 (permalink)
 
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WAAS/SBAS

The Garmin aera is listed as featuring WAAS/SBAS.

SBAS means 'Satellite Based Augmentation Systems' - the current SBAS are WAAS, EGNOS and MSAS which are mutually compatible to provide international SBAS coverage. These systems are satellite supported Differential GPS (DGPS) which is not the same as the 'Ground Based Augmentation System' (GBAS) which requires an additional receiver to provide DGPS augmentation. GBAS using VHF should provide sufficient accuracy for precision approaches in future years; GBAS using 300KHz MF/LF receivers is also available, primarily for maritime use.

The WAAS (Wide Area Augmentation System) is available in America, EGNOS (European Geostationary Navigation Overlay System) is the European equivalent, while MSAS (Multi-functional Satellite Augmentation System) operates in Asia, particularly in Japan.

EGNOS currently uses 2 Inmarsat and the Artemis satellites, but will later use new Astra satellites Astra 4B (due to launch in a couple of months time) and Astra 5B (due to launch next year).

Garmin EGNOS satellite IDs are 33 (Inmarsat 3F-2 at 15.5W), 37 (Artemis at 21.5E) and 39 (Inmarsat 4F-2 at 25E). The satellites are in geostationary equatorial locations, so are quite low on the horizon as well as being much further from the earth than the GPS constellation. Inmarsat moved its satellites over the past few years to optimise its global coverage; Artemis took nearly 2 years to reach the correct orbit after an Ariane 5 launch vehicle failed to deliver it correctly.

You will find a HUGE number of out of date websites and other erroneous information on the Internet concerning EGNOS satellites.

So yes, your Garmin aera should indeed be EGNOS capable. From Booker aerodrome, look in the arc between about 195ºT and 155ºT for EGNOS satellites.

Last edited by BEagle; 19th Feb 2012 at 09:44.
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Old 19th Feb 2012, 12:25   #12 (permalink)
 
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I thought I'd try an experiment. My wife thinks I'm gardening, but if that's not a good time to play with my GPS, when is?

Monitoring my Aera 500 in between feeding my new Bosch garden shredder (a device that can only possibly have been designed by an off-duty aeronautical engineer), I'm getting a consistent predicted accuracy of 10ft, and a periodic signals on satellite 37 and 39.

That seems to imply that BEagle is correct.

G
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Old 19th Feb 2012, 13:44   #13 (permalink)
 
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Quote:
As an avid Doctor Who fan of 30+ years standing....
So tell me, Geng-the-Eng, which one of the Doctor's assistants 'did it for you'?

a. Victoria Wakefield (Deborah Watling)
b. Zoe Heriot (Wendy Padbury)
c. Joe Grant (Katy Manning)
d. Sarah Jane Smith (Elizabeth Sladen, RIP)
e. Leela (Louise Jameson)
f. Nyssa (Sarah Sutton)
g. Tegan Jovanka (Janet Fielding)
h. Someone else

Glad to hear that your aera is receiving EGNOS as predicted. The accuracy figure you quote is pretty remarkable!
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Old 19th Feb 2012, 14:12   #14 (permalink)
 
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It is, although consistent with what various websites claim I should be getting with WAAS/EGNOS.

Somewhere between Leela and the first incarnation of Romana I think, although spending half my summer holiday when I was about 10 trying (and by and large succeeding) in making my own K9 may explain a lot about my personal and career choices since.

G
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Old 19th Feb 2012, 16:34   #15 (permalink)
 
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Thanks; home now, so I can play with my Aera 500. I just tried outside and gave up waiting for it to get a lock onto satellite 37 (it was flashing and showing a signal but it never went solid green; I decided it was too cold for sitting around outside). But clearly it thinks it can, so I guess it is going to work.

Tim
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Old 19th Feb 2012, 17:16   #16 (permalink)
 
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I just tried too, getting a 100% signal strength on satellite 33, but no solid green bar, just flashing grey.
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Old 19th Feb 2012, 17:21   #17 (permalink)
 
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Any modern GPS, especially one in that price range, ought to be EGNOS compatible.

My Garmin 496 certainly is, but quite often it doesn't seem to be receiving it. It seems about 50% lucky, despite having a remote antenna connected.

I got this interesting pic last year, but didn't make note of whether it was on EGNOS or not...



That level of vertical accuracy is not in itself exceptional; even my old KLN94 usually shows it within about 10-20ft of a known elevation when on the ground.
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Old 19th Feb 2012, 17:28   #18 (permalink)
 
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Regarding the satellite signal bar, the Garmin aera manual states:

Quote:
GPS Status can be helpful in troubleshooting weak (or missing) signal levels due to poor satellite coverage or installation problems. As the GPS receiver locks onto satellites, a signal strength bar is displayed for each satellite in view, with the appropriate satellite PRN number (01-32 or 33-64 for WAAS) below each bar. The progress of satellite acquisition is shown in three stages, as indicated by signal bar appearance:

- No bar—Receiver is looking for the indicated satellite
- Gray bar—Receiver has collected the necessary data and the satellite signal can be used
- Green bar—Satellite is being used for the GPS solution
Since the EGNOS signal is merely a corrective augmentation, I can't really see how it is used as a source for the GPS solution itself as the vehicle is in a geostationary location. The manual also states that the Receiver Status field gives the following information concerning SBAS corrections:

Quote:
When the receiver is in the process of acquiring a 3D differential GPS solution, "3D GPS Location" is indicated as the solution until the 3D differential fix has finished acquisition.

“3D Differential” appears when you are receiving DGPS corrections in 3D mode.
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Old 19th Feb 2012, 17:57   #19 (permalink)
 
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Thanks, BEagle.
I was still getting "3D GPS Location", albeit with 10ft reported accuracy.
I will loiter a little longer tomorrow, and see whether it changes!
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Old 20th Feb 2012, 17:23   #20 (permalink)
 
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2Carrot

Same here - I'll post if I ge anything different

Tim
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