SBAS

[docdic]

Contributors to these forums write about testing their GPS devices for EGNOS/WAAS in various countries and in parts of this country.

I have a Holux GPSlim,and iPAQ 5555 and use Memory Map and GpsGate NMEA Logger and use them primarily for walking in the Brecon Beacons.

I also have EMTAC and VisualGPSce installed for information/interest only.

It is possible or even likely that I cannot receive EGNOS/WAAS signals here anyway, when they are switched on, at present but, even if I enable this facility in the Holux with GPS Viewer, how would I know whether or not I am receiving them?

Is there a readable SBAS signature somewhere and would I notice specific characteristics when using it if I were able to receive it?

docdic

[uffe73]

I would suggest you install spGPSView on your iPAQ and switch on WAAS/EGNOS from there instead of using Holux GPSViewer. The thing is that you need to switch, temporarily, from NMEA mode to SiRF mode in order to enable WAAS/EGNOS. Holux GPSViewer tries to enable the feature by sending an NMEA command ($PSRF108,01 <CR> <LF>), which isn't part of the standard SiRF command set. It thefore has no effect. It's strange that Holux hasn't updated the tool with regards to this! Another PPC tool that can probably be used for enabling WAAS/EGNOS is SiRFDemoPPC, but I don't know where to obtain this program. You can also do it in SiRFDemo in Windows if you have a cable to connect your receiver to your PC.

Once you have switched on WAAS/EGNOS in spGPSView and returned to NMEA mode you should be able to detect DGPRS Fix in VisualGPSce (at the bottom of the screen). The colour of the blinking dot changes from green to blue. Another way to detect it is to look at the $GPGGA command in an NMEA log and especially the 6th parameter. If it show a 2 you know that you have DGPRS Fix.

In my experience you can only maintain a DGPRS Fix for a few minutes while driving in a town. I think the main reason is the low elevation angle of the ESTB satellite (PRN120) where I live. If you're in the UK the angle should be a little bit higher since you're closer to the equator. The best conditions for testing out the WAAS/EGNOS capabilities of your receiver should be while standing on an open field with no obstructing buildings or trees. I haven't had time to do any serious testing to see if I actually get an enhancements of the position accuracy. But I can see that I get DPGRS Fix once in a while. If you are able to measure any accuracy improvments due to WAAS/EGNOS I would be very interested to hear about it - purely out of curiousity. The only method I can think of is to take two NMEA logs of a certain route - one with DGPRS Fix and one with normal 3D Fix. If you plot both of these logs at the same time in a map program you should hopefully be able to notice a difference.

Good luck,

Ulf
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Garmin GPSMap 60CSx (SW ver. 3.70)

[uffe73]

[uffe73]

[docdic]

Ulf,

Thank you very much indeed for your very clear and helpful response to my query – I am very grateful.

I downloaded spGPSView this afternoon. I put my Holux 236Slim on the window-sill of my bedroom and tried to make sense of the commands and sub-command parameters.

I have a wish list of two and further questions – I wish that there was a help file and I wish that user settings would remain set, even after switch off, unless and until they are changed again by the user.

My questions relate to the Commands –

what is StaticNav – when should it be on or off?

What should the Msg rate be? – although I am not aware of having changed any rates, and it might be my imagination, but the red blinking fix dot in Memory Map appears to be blinking more slowly since “playing” with spGPSView

Should “Set WAAS” be set to ON or to OFF while still in NMEA mode or after changing to Sirf mode? It tells me that the setting has failed if I try to do it in Sirf mode but there is nothing to say whether the setting is on or off anyway. It does, of course, say whether or not it has a fix but, if there is no fix, there is nothing to say whether this is because the satellite is not in view or because the setting has not been accepted.

Sometimes some of the commands are greyed out but not at other times but there does not appear to be any fixed relationship to any other settings – there obviously is but I can’t see it

NOW – having just typed this into my word processor in order to post this back to you on the forum, I have been back to my Holux and iPAQ and SURPRISE, SURPRISE – I have a DGPS fix – confirmed by spGPSView, Emtac, and VisualGPSce. It is 15.31, my window faces east, overlooking a valley towards a near mountain in the Brecon Beacons and I am at approx. 230m altitude.

I was able to keep the fix for ten minutes and then lost it but, with reference to my comments above, I don’t know whether that was because the satellite had dipped out or because I was trying various settings and just couldn’t get back there.

One last question – you suggest keeping two logs, one of NMEA output and one of Sirf output at the same time. I can keep two logs with GPSGate but will the Holux put out both at the same time? If so, it seems strange that one has to send commands to it to change from one to the other.

Regards,

docdic

[uffe73]

Hi Docdic,

[docdic]

Ulf,

Greetings –

Thank you for your further message.

I wasn’t wishing that the GPS would keep its settings – I was wishing that the applications – like spGPSView – would keep their settings until changed, and I’m beginning to wish that the GPS would lose its settings -

I suppose that it is a case of …if there isn’t a Help File, steer clear of it - it might bite…

I have looked at the message frequency command and every item shows as a ‘1’. I have changed GSV to ‘5’ but each time that I go back in it shows a ‘1’ again.

Now, however, the orange light on the Holux stays on for 6 seconds and is off for 6 seconds, giving a cycle frequency of 12 seconds and the red dot in Memory Map flashes on for 3 seconds and off for 3 seconds. The Track Update setting in Memory Map is set at 1 second. The Holux certainly used to flash at 1 second intervals.

I have tried to change the settings back in spGPSView but, as all settings show ‘1’ anyway, I don’t know whether or not it is doing anything.

Now I have difficulty in getting back into spGPSView – I keep getting “Not Connected” – “GPS Protocol Error” – “Get Protocol Timeout” – and it all freezes. I suppose that the GPS is so slow in sending out data that the program times out before the next signal reaches it.

Do you have any knowledge of how I can return the GPS to its original serttings?

Regards,

Docdic

[uffe73]

Hi Docdic,

You seem to be unlucky with your equipment. I'm not using MemoryMap so I can't really comment that. But the blinking on my Holux GR-213, after acquiring fix, occurrs roughly every 1-2 seconds. 12 seconds cycle time sounds too much.

[docdic]

Ulf,

Greetings –

Thank you.

I had already tried Factory Start. I am not certain that it means “Factory Reset”, but it made no difference anyway.

I left the battery out for 18 hours but that made no difference.

After fiddling about between spGPSView and GPS Viewer today , it alternated between slow and normal rates for a while and then started, apparently spontaneously, to blink at the normal rate of once per second and has continued at that – so far…

It is a pity that there is no User Manual with the spGPSView because it makes me a little reticent to change to Sirf and try to get DGPS if the effects are unwanted and there is nothing to indicate why it happened or, even, why it reverted to normal activity.

Being an ignoramus in these matters, I have another question –

What does Sirf III actually do?

I understand that Sirf II is vastly better than Sirf II and my Holux is undoubtedly vastly better than my old Magellan, which did not use Sirf at all, but, as Memory Map does not recognise Sirf and will work only with NMEA, am I losing out on the benefit of Sirf or does it relate only to the reception of signals from the satellites and not to the sending out of signals to the iPAQ? Is the end result the same whatever form – binary or NMEA – that is being sent out and being received by the Pocket PC/PC?

Regards,

docdic

[docdic]

Ulf,

Thank you again.

I seem to be using you like a textbook, for which I apologise.

However, questions beget questions –

Today, with cycle frequency correct still, I have noticed two things:

1. With WAAS enabled and enablement confirmed in Nav Params, I get a 3D + DGPS confirmation notice in Emtac and VisualGPSce (with blue flashing dot) and a ‘2’ in the sixth parameter of GGA, - but spGPS itself says that there is no DGPS – why should this be?

2. Sirf frequently tells me that it is tracking only 4 – 6 satellites, although 10 – 11 are in view, whether DGPS is enabled or not, whereas NMEA tells me that it is tracking 10 – 11 satellites at the same time. Why should this be?

Does enabling WAAS in spGPSView automatically cause the Holux to receive from all of the satellites which give DGPS, including EGNOS? I ask because I see references to setting PRN numbers in various threads.

I take it that whoever wrote the spGPS ( and similar programs ) assumed that whoever would use it would understand all the various aspects of it. I don’t but would like to – can you point me to where I might discover what all the commands and response data mean?

With many thanks,

Regards,

docdic

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