WAAS in AUS?

Richary · Post by **Richary** » 31 August 05 1:10 pm

Does anyone in an area receiving the "WAAS" signals have a laptop, CF GPS card and a copy of GPS Info? That might give some more idea of what is being received (assuming the CF cards are WAAS compatible).

riblit · Post by **riblit** » 31 August 05 3:19 pm

The <a href="http://www.trimble.com/gps/why.html">Trimble tutorial</a> I mentioned in a previous post in this thread has a bit to say on the subject of frequencies and the Psuedo Random Code:

Trimble wrote: A Random Code?

The Pseudo Random Code (PRC, shown above) is a fundamental part of GPS. Physically it's just a very complicated digital code, or in other words, a complicated sequence of "on" and "off" pulses as shown here:

The signal is so complicated that it almost looks like random electrical noise. Hence the name "Pseudo-Random."

There are several good reasons for that complexity: First, the complex pattern helps make sure that the receiver doesn't accidentally sync up to some other signal. The patterns are so complex that it's highly unlikely that a stray signal will have exactly the same shape.

Since each satellite has its own unique Pseudo-Random Code this complexity also guarantees that the receiver won't accidentally pick up another satellite's signal. So all the satellites can use the same frequency without jamming each other. And it makes it more difficult for a hostile force to jam the system. In fact the Pseudo Random Code gives the DoD a way to control access to the system.

But there's another reason for the complexity of the Pseudo Random Code, a reason that's crucial to making GPS economical. The codes make it possible to use "information theory" to "amplify" the GPS signal. And that's why GPS receivers don't need big satellite dishes to receive the GPS signals.

We glossed over one point in our goofy Star-Spangled Banner analogy. It assumes that we can guarantee that both the satellite and the receiver start generating their codes at exactly the same time. But how do we make sure everybody is perfectly synced? Stay tuned and see.

Each GPS satellite transmits two carrier signals in the microwave range, designated as L1 and L2 (frequencies located in the L-Band between 100 and 200 MHz). 
Civil GPS receivers use the L1 frequency with 1575.42 MHz (wavelength 19.05 cm). The L1 frequency carries the navigation data as well as the SPS code (standard positioning code). The L2 frequency (1227.60 MHz, wavelength 24.45 cm) only carries the P code and is only used by receivers which are designed for PPS (precision positioning code). Mostly this can be found in military receivers.
<img src="http://www.kowoma.de/en/gps/GPS_satellite_signals.gif">

Kerry · Post by **Kerry** » 31 August 05 5:17 pm

Hopefully there will be a tutorial re-write/update in the very short term, much is getting almost a little outdated!

Cheers, Kerry.

Kerry · Post by **Kerry** » 31 August 05 6:51 pm

Had a quick look for anything that might resemble a WADGPS signal this afternoon and drew a blank. The only thing that was obvious was that anything that is "WAAS" related (such as POR/PRN134 #47 to a Garmin) is not even being searched for, not being allowed as per the firmware update.

As expected for Garmin with up to date firmware.

Those with Magellans need to note the satellite # if in fact it is available straight off the screen?

Cheers, Kerry.

GIN51E · Post by **GIN51E** » 31 August 05 7:07 pm

well we don't get a sat number just a W but in the screen you use to turn it off its full of all sorts of numbers ect, so i'll see if i can pick it up tonight and put all those numbers up and see if anyone can make sense of it.

riblit · Post by **riblit** » 31 August 05 7:44 pm

GIN51E wrote:well we don't get a sat number just a W but in the screen you use to turn it off its full of all sorts of numbers ect, so i'll see if i can pick it up tonight and put all those numbers up and see if anyone can make sense of it.

If you can capture the NMEA data stream (its text format, so you can use any terminal program - or try googling GPS Diag, its freeware) the satellite numbers will be in the data

riblit · Post by **riblit** » 31 August 05 7:46 pm

richary wrote:Does anyone in an area receiving the "WAAS" signals have a laptop, CF GPS card and a copy of GPS Info? That might give some more idea of what is being received (assuming the CF cards are WAAS compatible).

I'm not sure that they are. My GPS mouse isn't.

Kerry · Post by **Kerry** » 31 August 05 7:50 pm

GIN51E wrote:well we don't get a sat number just a W but in the screen you use to turn it off its full of all sorts of numbers ect, so i'll see if i can pick it up tonight and put all those numbers up and see if anyone can make sense of it.

If you can view/record GSA/GSV NMEA sentences things should show up in these. The non GPS ones generally will only have a number and SNR, no azimuth or elevation.

GIN51E · Post by **GIN51E** » 31 August 05 9:24 pm

ok well no luck, couldn't get a fix on WAAS but i took a pic of the screen anyway in which it says i think SRCH meaning its searching for those sats but weather they are the ones which were giving me the WAAS message i'm not sure, i found another screen which has a huge list of sat stats and numbers but i guess they don't mean much if i'm not logged onto them?

also found another screen which had a record of some sort of errors and the date they occured, not sure what thats about but it amazing the number of setup and info screens it has. just wish i knew what they all meant.

But i do remember when i went into this screen on the weekend whilst i had a WAAS lock it did have heaps of numbers jumping around all the time, i'll keep an eye out over the weekend and if i get a WAAS log i'll try and get a photo of all the stat screens.

riblit · Post by **riblit** » 31 August 05 10:11 pm

On the screen:
Sat - Satellite Number - I'm not sure how Magellan numbers the sats.
State - its searching
SNR - Signal to noise ratio - indicates the strenth of the incoming signal.
Az - Azmuth - the horizontal angle in degrees to the satellite from your location. 0 = 360 = North.
El - Elevation - How high in the sky it is. 0 = horizontal 90 = Vertical

Bottom set - not too sure.

Kerry · Post by **Kerry** » 31 August 05 10:27 pm

Your in the right screen but obviously currently just searching, no SNR, no lock.

137 is MTSTAT2 (has it even been launched?)
129 is MTSTAT1R which was launched Feb 2005, sits just north of PNG at 140E.

Coincidence or not that it just happens to be searching for 2 satellites from the same WADGPS?

Cheers, Kerry.

Damo. · Post by **Damo.** » 31 August 05 10:27 pm

riblit wrote: Bottom set - not too sure.

That's the screen that comes up when you follow the "secret" instructions to switch off WAAS. You then switch the on to off to disable it.

GIN51E · Post by **GIN51E** » 31 August 05 10:45 pm

here is a few more scrrens,

which one would be best to photo when i get a WAAS lock?

or

also here are the other screens available if anyone knows what they mean.

I'll keep WAAS turned on for the moment so if i get a lock i can hopefully get a photo of the required screen so we can work out what its picking up exactly, i'll have it on at TAFE tomorrow and Friday and Saturday as i head up towards Bathurst but if i don't get a lock again i'll turn it off and say it was a fluke.

Damo. · Post by **Damo.** » 31 August 05 11:06 pm

I just tested my Magellan Meridian. With WAAS switched on it was picking up only 4 sats in my backyard (buildings on two sides) # 20 16 25 24. And also a W. Switch off WAAS and the W disappears.

riblit · Post by **riblit** » 31 August 05 11:11 pm

Damo. wrote:I just tested my Magellan Meridian. With WAAS switched on it was picking up only 4 sats in my backyard (buildings on two sides) # 20 16 25 24. And also a W. Switch off WAAS and the W disappears.

Do you have the screen GIN5E first posted, if so what sat number showed on it?