"Lost satellite reception"

[Greg Masters]

Following PanEuropean's enquiry (here) about WASS and satellite 44, I've been riding around a bit today with the GPS on the GPS Info page to see how often sat 44 connected.

The answer to that was easy - I didn't see it at all!

But what I did notice was that Betty was telling me more often than I am used to "lost satellite reception".

Woz going on? Have they turned the wick down on the satellites? Is the aerial on the 2610 not as good as on the SPIII? Is my Touratech mount shrouding reception? Is it the weather? Are the Ruskies up to something?

Any answers?



Greg

 

[Howard Millichap]

Depends where you were riding. Tall buildings or dense forest will obscure the signal.

 

[Frank Warner]

As will a dense head.

"But officer, if I don't drink I loose GPS navigation!"

 

[PanEuropean]

Greg:

Thanks for your very interesting observations. I have been experiencing the same thing myself, both in Europe and in Canada.

When you turn on SBAS (WAAS) augmentation, two of the twelve channels that are normally available to receive the 'standard' GPS satellites are dedicated to searching for augmentation satellites. This means you now have - in a manner of speaking - a 10 channel GPSR, not a 12 channel one.

When the European SBAS system goes fully operational this summer, the augmentation satellites will transmit both ranging information and correction information, meaning, a SBAS satellite will also be able to perform the regular work of a normal satellite, allowing the GPSR to use it to do the triangulation needed to determine position. But right now, the European augmentation satellites are only transmitting correction information, not ranging information.*

This means you have fewer channels available to track the satellites you need to track to get a position fix. It is true that you only need 4 satellites to get a fix, but the design of the receiver is such that each satellite in view is assigned to a channel, and when that satellite disappears from view (vehicle goes past a building that blocks view of the satellite), that channel remains reserved for that satellite for a little while, in case it comes back into view. So, with only 10 channels dedicated to ranging information, your GPSR is not quite as capable with WAAS turned on as it was with WAAS turned off.

All this should sort out later this year when the ESA switches over from the EGNOS testbed (ESTB) to the fully functional EGNOS system. For example, I am in Canada now, getting the US WAAS signal, and I get solid signal strength bars from the augmentation satellites, which means they are transmitting ranging data as well as correction data. In Europe, I only got hollow bars from the augmentation satellites (in simple terms, a hollow bar means the satellite cannot be used for determining position).

I now use an external antenna on my car and motorcycle whenever I have WAAS on my SP 2620 or 2650 turned on. It makes an amazing difference to signal strength. I don't know why I need an external (amplified) antenna with WAAS on, but don't need one with WAAS off. I have a feeling Garmin is working pretty hard on this one - witness the length of time since the beta release of 2.95 and now - still no final release, tons of work being done, I have upgraded software 4 times since 2.95... I think you see what's happening.

I am beginning to think that this whole WAAS thing is just one big PITA for automotive GPSR's, although it is very valuable for aviation use.

PanEuropean

*Strictly speaking, the ESTB satellites are sometimes transmitting ranging information, but they are also flagging it as 'do not use for navigation', and Garmin respects those flags, so the GPSR will not use satellites flagged that way for a position fix.

 

[Greg Masters]

This means you now have - in a manner of speaking - a 10 channel GPSR, not a 12 channel one.

Michael

I knew you'd have a good idea of what is happening!

I don't plan to be out on the BMW for a few days now, but when I do, I'll try running with the WASS un-enabled. I was out and about again today and it occurred to me that the 2.95 allows the user to switch between WASS enabled and un-enabled. If there wasn't a potential downside to having it enabled, why make it switchable? Unfortunately, until I read your reply, I didn't work out the answer!

I'll let you know how it works out.

As an aside, London is not particularly good for Garmin Sat 44 - the elevation is, in the main, only around 50 feet or so, a few hills to the south, a few tall buildings and Sat 44 pretty low on the horizon. In a few weeks, a bunch of us are off to Poland. That should give a good opportunity to see how well the 2610 can work with WASS in the present Sat-Nav regime. However, I look forward to the European sytem being fully commissioned.

Greg

 

[mrTickle]

I also had this problem but I put it down to my new cars windscreen . I'll disable that pesky WAAS for now and hopefully everything will be OK again.

Thanks to Pan for sorting this one out