PLC

I have a Globalsat 307 and it works great!

But it does not have XTRAC firmware like the Sysonchip so it can only use satellite signals greater than 26db

XTRAC can use signals as low as 16db

There are many places that I cannot get a signal and I would like to see what strength level the signals are at.

Problem is all utilities I have ONLY SHOW satellites in view and then their signal strength IF IT IS ABOVE 26db.

If it is below 26db it does not show anything except that the satellite is in view... I would like to see the signal strength of these satellites to see if they are above 16db

if so, then I can conclude that XTRAC would be better for me.

Anyone know GPS utilities that will do this?

TIA

JakeRich

Quote:

Originally posted by PLC I have a Globalsat 307 and it works great! But it does not have XTRAC firmware like the Sysonchip so it can only use satellite signals greater than 26db XTRAC can use signals as low as 16db There are many places that I cannot get a signal and I would like to see what strength level the signals are at. Problem is all utilities I have ONLY SHOW satellites in view and then their signal strength IF IT IS ABOVE 26db. If it is below 26db it does not show anything except that the satellite is in view... I would like to see the signal strength of these satellites to see if they are above 16db if so, then I can conclude that XTRAC would be better for me. Anyone know GPS utilities that will do this? TIA

I have used the Fortuna XTrack receiver and in the normal mode it is just as sensitive as any other CF GPS. In the XT mode it can use weaker signals, but it is very, very, very slow to do that. Most of the time it was in the 7-10 second range behind where I was. For walking, that's fine, but for driving it was not usable in that mode. The XT mode is really for hiking, uban canyon walking and maybe off-roading that involves slow movement. The delay in signal processing means that it simply is too far behind to be used in a car at almost any speed over 5 mph.

The point of that discussion was that you don't need to see the signal strength to make the decision if XTrack is better for you.

First, why does the Globalsat lose lock? Is it because of the sky being blocked by buildings? Is it because of blocking from being poorly positioned in your car? If the answer is yes, then the Xtrack won't be able to get a fix either. It still needs a reliably clear view of the sky. It just works better in weakened signals like under trees, or when part of the sky is totally blocked by some structures or really severe thunderstorms, etc., or when the satellites directly above you are blocked but the ones on the horizon are visible but weak (under an overhang). If the Globalsat is suddenly losing ALL signals, like under really big overpasses, in tunnels, etc, the Xtrack won't do any better.

Then answer these questions:

When the Globalsat loses lock will I be moving slowly enought that I can tolerate a 10 second delay in calculating location to maintain that lock?
Is that same 10 second delay acceptable all the time? (Bear in mind that to change from normal to XT mode you have to remove the CF from the slot, move the switch and then COLD start the receiver (3-5 minutes, minimum), so it's not something you do "on the fly."

If the answer to either question is "no," then the XT is not for you. If the answer to both is "yes," then by all means the XT will be useful.

In direct answer to your question, I don't know of any software to show the satellite strength below the threshold. I'm not even sure if they actually send a NMEA statement on any satellite below the threshold. If they do, then you could use any of the utilities that capture the raw NMEA statements and use this information to parse out the information. This is the structure of the NMEA statement that sends satellite information:

GSV - Satellites in view
GSV,2,1,08,01,40,083,46,02,17,308,41,12,07,344,39, 14,22,228,45*75
2 Number of sentences for full data
1 sentence 1 of 2
08 Number of satellites in view
01 Satellite PRN number
40 Elevation, degrees
083 Azimuth, degrees
46 Signal strength - higher is better
<repeat for up to 4 satellites per sentence>
There my be up to three GSV sentences in a data packet

PLC

Thanks for reply

I thought the Fortuna XTRAC only lagged part of the time... not ALL THE TIME. Are you sure it is most of the time?

If possible could you test and give me a % of the time it truly lags?

I read a report that it only lagged a small % of the time and that the lag was less than 5 sec.

If it truly lags more than 80% of the time then no I do not want it.

Why dont they put a faster ARM processor in the XTRAC units so there will be no calculation lag, and charge more for the unit?

FYI I lose signal in urban canyons like downtown NYC near Wall St.

JakeRich

The Xtrack in the XT mode lagged almost all of the time, it was rarely within 5 seconds of my location, even with full satellite strength. The lag varied, averaging about 7-8 seconds, sometimes as much as 10 seconds. The Digital Signal Processing it uses to allow it to use weaker signals is very, very math intensive, using recursive calls of complex formulae to continue processing until it has milked out of the noise every part of the signal it can. I am sure that someone will make a faster processor for it, if the demand is there, but it will be very expensive in comparison to "normal" receivers. I'm actually surprised they can do it at all!

If you are walking in NYC, it's might work for you in the canyons of Lower Manhattan. In a car, it's not as useful in the XT mode, IMHO, although it is certainly better than nothing. I did review it a little while ago and that review is in the review section here on Aximsite. It's a great idea for walkers in urban canyons, hikers, mountain bikers, cross country skiers and maybe off-roaders not totally bent on high speed, but for so-called normal driving the lag is really noticeable. In the ST (standard) mode, the lag disappears, but so does the DSP processing and it becomes a competitive CF GPS that is as good as any on the market. As I indicated in the review, a good use would be to leave it in ST as you drive to the parking area, then switch to XT and as you prepare to leave on the hike/trek/bike/whatever it can reaquire the fix (cold start, remember) and you are off! When you get back to the car you swap back to ST and while you are packing up to leave it requires again and you are in business. Using that methodology, it is very attractive to those folks who do that sort of thing.

Maybe someday the swap from ST to XT can be automated based on the signal strength and some sort of indicator used to let you know what mode it is in. If that happens, then most of the time it will have little or no lag and then it will lag when it goes into XT mode. However, in the present incantation the XT delays are there whenever it's in XT mode.

Any other users of the Xtrack want to share their experiences?

PLC

Thanks for the info

Since you have the Fortuna I suppose you could test it this way... if you were really interested hehe.

Leave it in ST mode until it loses a signal. Then switch it to XT mode to see if it can re-acquire that signal.

I suppose this would only work walking since you would have to stop and reset.

If you have the time it would be nice to see some real-world examples of where XT really does help over ST mode.


Of course if we could just see the signal strength of ALL satellites in view (not just the ones over 26db strength) then we could make that determination for ourselves.

But someone would have to write a new program...

JakeRich

I don't have the XT anymore. I reviewed it and them sent it on. I did go under some heavy trees until it lost signal in ST mode and then put it in XT and it got a fix. I also tested it inside some buildings where I was never able to get a fix with "standard" gps units and it did get a fix there as well. The XT is amazing at how it can use really poor signals to get a fix and in the right circumstances would be really good. Even driving the XT mode is better than nothing, but you have to be aware of, and live with, the delay in displaying position. If I were a trucker who went to urban canyon addresses in heavy traffic and wanted to have some mapping, the XT mode would work to get me on the right block. The 10 second delay may mean I pass the actual address before it tells me I am there, but as long as I remember that I can be looking for my destination in advance and be confindent I am at least in the right neighborhood.

On moving highways where you are travelling at higher speeds, 10 seconds behind could mean as much as 700-800 feet, but generally on those highways you have a clearer view of the sky and don't need XT, just the ST mode. For driving out of or into an urban canyon, however, the problem is swapping requires removal of the unit, movement of a switch and then a cold restart. All of that is not safe to do while driving so you would either have to stop or have a passenger do that for you.