The Great Big SPOT Thread

Actually, It's a 6 layer board.

You're from Belgium? One of my favorite places! If you drink beer, have a lovely Belgian Trappist Ale for me!

Putting it on a metal surface does almost nothing. It might help both reception and transmission by a dB or two at the very most (due to a weakly coupled additional ground plane) but that's about it. It definitely doesn't hurt anything. The hood of my truck is a favorite place for me to lay mine while it sends a check-in message.

Both the Globalstar satellites (that the SPoT transmits through) and GPS satellites are in an inclined orbit. Above 50 degrees or so (even above 40), your best view of them is biased to the south. As evidence of this, I was recently in Lugano Switzerland (visiting Nemerix, BTW). Latitude is about 46 degrees north. I had a room in our hotel with a balcony facing almost due north. My colleague was across the hall, with a balcony facing almost due south. The balconies had a rather long concrete overhang above them. On my colleague's balcony, our SPoTs worked almost as well as they might in a wide open field. On my balcony, facing north, they barely worked at all. It was a bitch even getting them to get a GPS fix, nevermind getting a transmission through. You will also tend to have a bias on transmission in the direction of the nearest Globalstar ground station.

Here in the New Orleans Area, latitude 30 degrees north, we notice almost no directionality. That is, if your SPoT see's only the northern half of the sky here, it's performance is about the same as if it sees only the southern half. (Not terrible, either way).

You are quite correct.

The LED's in the SPoT cannot produce amber. They are red/green bicolor LEDs.

Some red/green bicolor LED's can look amber-ish if you light both the red and the green half. These don't. I've put custom code in the SPoT to do that to see what happens. When you light both the red and the green in these LED's, you get a red that's shifted just a tiny bit more orange than their normal red. You have to really look closely to tell the difference between what you get in this case and the normal red.

In any case, the firmware in the SPoT never lights both the red and green at the same time anyway.

I'll be crossing the border at Mcallen TX Saturday heading down to Veracruz for a few days. My wife talked me into buying the Spot unit mainly to make her feel better. I've been testing it out and it seems to work well. Be interesting to see how it works out on the trip.

I was actually trying to brag about how cool SPOT is, and then I wasn't sure I was doing it right. I wish the instructions were printed right on it, the way they are printed on my PLB. Open the cover of the PLB, and right there, in plain English- INSTRUCTIONS! For this prospector guy, working for a major mining company, a SPOT or SPOT-like product would be perfect. Meanwhile, like me, he's carrying a heavy Sat phone.

I confess that I do not know colors. Maybe it was flashing fine. I have already posted my feeling on ease-of-use. I am carrying the instructions but at this point in my trip and my opinion of SPOT, the only thing I'll use it for is to press 911.

For a trip of this length, renting an Iridium Sat phone costs less than buying a SPOT and upgrades. If you're traveling in Mexico, I think Globalstar coverage is supposed to be pretty good, and they're cheaper then Iridium. Doesn't SPOT use Globalstar satelites?

I did not get a replacement unit because 1) I did not have time, and 2) testing it in Wisconsin it worked perfectly.

I am carrying 4 extra lithium batteries. Lithium batteries are easily available in Central and South America. I have seen them in gas stations and grocery stores and they cost the same here as in the US. Lithium batteries also last a lot longer in my GPS than regular batteries. I run the GPS directly off a 12v plug on the bike, but it's nice to have the GPS running if the bike is off. It's easy to install an extra 12v outlet.

Luckily, there are not any Walgreens here. At least I haven't seen any.

If you're in Mexico, and you happen to run into the kinds of cops they have in Peru, how is SPOT going to help you? If you carry a Sat phone, you can write down the number of the US consul, or even put it in the memory. You can also make sure your emergency contact people have the right numbers.

I know SPOT is going to save some lives, but I also wonder, how many lives will be lost because people thought they could rely on it? I suppose that if you put it on Traking mode, it might help rescuers find your body.

i hope that people don't think that this is device is a replacement for a sat phone but that it is something that augments this, much in the way that you are using it. it's an inexpensive backup and possible alernative to a phone call but will not replace the funtionality of a phone.

On a recent ride to Baja (see B.A.R.F. in ride reports), I had a lot of trouble calling home. But I was sending "OK" messages home 2 or 3 times a day, and that kept me out of hot water for not calling more. Of course, my wife had to ask my son to open the emails and report on my current location. :huh I ran the tracking most of the trip but opening that is way beyond what my wife will attempt on the computer. Had I not had the Spot, I'd have had to spend a lot more time and energy finding a way to call home. I tried a globalstar sat phone a few times and it was always a PITA to get coverage. Worked well when you had coverage but getting coverage was iffy. The spot always worked as far as I could tell.

Thanks. I wanted to say that all the components are on either side of a single PCB (as far as I saw). Thus no stacking.

The patch antenna is much larger than the ones we're used to see in antennas for GPS receivers and thus should have greater apex gain (Emtac reported 0 dB for 12 mm patch antennas, +5 dB for 25 mm antennas. This one is double that.)

I have read that the slot allows designers to achieve dual resonance frequencies. It appears to a radio amateur, which I am, that the radiation pattern of the slotted antenna could be a lot more irregular than that of a single frequency narrow bandwidth antenna and thus add an element of unpredictability for satellite uplinking. This at least for non repeated messages.

Would you have any comment on this?

Thanks for your valuable comments on the effect of going to high latitudes. I believe it is important for users to understand this, e.g. if you are in a forest in northern Sweden (65 degrees north) , be sure to be in the northern side of an open area in order to get as good a view south as possible. With dense forests, such as in British Columbia, finding an opening might be difficult. It would be interesting to have test results from such areas.

Does it help to tilt the device somewhat towards the south - or rather in the direction of a ground station? For the simplex ground station in France, this would mean aiming the unit about SW if you're in Sweden. (There is a European ground station south of Sweden, but it seems dedicated to phone only).

Global Star's map of simplex coverage shows ground stations in Europe in SW France and in Turkey. However, the Phone coverage map shows a ground station in also in Northern Italy plus one or two in Russia. Over all, simplex coverage appears much more limited than Phone coverage and not all Phone ground stations will receive simplex communication. Furthermore, different Global Star maps are not consistent as it comes to ground stations.

Using the SPoT attached to a belt, be it in a ventral, dorsal or lateral position seems to be pretty suboptimal if you want to use tracking mode - or any other mode for that matter.

While walking around in Whistler village, B.C. (abt 50 degrees North), holding the SPoT in my hand, I noticed that the unit lost its fix in open streets. There was non synchronous flashing. I believed this was due to dense multipath signals because of metallized windows. Would you have any comments on the GPS receivers vulnerability to multipath?

I also noticed that there is synchronous blinking for several minutes (10 in the event) even if you enter e.g. an underground garage under a five storey building, where it is dificult to believe that the unit would get a GPS signal. How soon will the unit report a lost fix?

What happens if you pass an object, such as a house or a tree, which blocks GPS signals for a couple of seconds just before the unit plans to transmit, will the position be extapolated or will there just be a postponement of transmission?

Having the buttons and the LEDs on the front side makes the user prone to hold the unit so that the LEDs are easily visible. For the first week of trials I held the unit vertically in my hand, also drawing from my experience with hand held GPS receivers which often have internal vertically mounted quadrifilar helical antennas (Garmin 76C is one example). This proved to be wrong. "Logo up" is still ambiguos and the manual only mentions that the Logo should face the sky when the unit is in water, on the last page. They could have said: The unit's antenna is between the buttons and the SPoT logo. Turn the unit so that the Logo faces the sky and avoid having your hand cover the antenna.

I agree with Banaman that there should be more explicit instructions on the unit. But not in the form of metallized stickers that risk blocking transmissions if put in the wrong place. A further note to Bananaman: You are not alone in trying to evaluate the SPoT with a critical eye to understand its limitations for the good purpose of getting the best result from it when it is really needed. So let's just report our sometimes negative results in an objective manner. Btw, if you check the map of Global Star Simplex Coverage, you'll see that Primary coverage ends at the peruvian-Chilean border

http://www.globalstar.com/en/satellite/simplex_coverage.php



There is an obvious dilemma: SPoT marketing oversimplifies the use of the device (IMHO). OTOH, if this makes more people buy it, some might be saved which would not have had it if a more complex picture had been presented (it seems that many units are bought by wives or parents). Some might also die because of insufficent understanding of the limitations. By providing more information in forums the implications of the dilemma are reduced. Some might even go from considering a SPoT to buying a PLB (in countries were these are allowed for land use - not all, notably the UK). I for one wasn't aware of land use of PLB until I learned about the SPoT. It was allowed in my native country Sweden only last year.

A note on SMS messages. European operators rarely offer the personal phonenumber @ operator.com mail2sms service which many Northamerican operators do and which Spot SMS delivery depends on. The rep office for Europe told me the other day that SPoT will offer a common SMS gateway for European users. This is welcome news.

Spotmaker, if your wanderings bring you to Brussels, there are 200+ beers here to try out. Not all are as strong as the ones named Delirium Tremens and Mors subite (Sudden Death), but still taste a lot better than Budweiser - subjective opinion - . Just PM me.

Golbalstar is extremely strict about certifying a transmitter or antenna pattern for their network.

As a result, that antenna is optimized for it's radiation pattern on the transmissions to Globalstar's network (otherwise, they wouldn't have certified it) and sacrifices a little bit of pattern symmetry on the GPS (compared to a dedicated GPS antenna). Interestingly, GPS gain is biased slightly in the direction of the buttons and LED's, which means GPS sensitivity is rather crappy on your belt. Flat on it's back is truly best. If hiking, with a backpack, the optimal way to carry it would be to wedge it inside a compartment of the backpack with it's face facing up (as much as possible). Any fabrics that backpacks are made of are transparent to the RF, as far as I know. Or, clip it to the backpack strap, with it's face facing up, as much as possible.

The transmit pattern, on the other hand, is an even broad cone-shaped pattern. It's very close to Globalstar's ideal example of what a simplex transmit antenna is supposed to do on their network.

Maybe, but be careful not to overdo it. The radiation pattern is very broad. With the unit flat on it's back, the pattern is quite even in a cone from about 10-15 degrees from horizontal to 90 degrees straight up. So, if you tilt it more than 10 - 15 degrees, you're doing little more than sending potentially useful RF energy into the ground.

Safest bet for optimum transmission performance is always to have the unit laying flat on its back. However, if you're at a latitude greater than 45 degrees north or so, a clear view of the southern sky is important. The further north you go, the more important a clear view to the south is and less important the view to the north is.

True, some of us actually argued against the unit having a belt clip, as it may be misleading. It's performance is spotty if worn on a belt. (The other side of the argument, of course, is ease of carrying the unit over a variety of situations.)

Actual multipath conditions don't bother it much. "Multipath", in this case, being defined as a mixture of direct and reflected signals, assuming they are all above the receivers sensitivity threshold. I'd guess if you lost GPS lock it was plain ol' signal attenuation from the tall buildings blocking GPS signals, as opposed to reflecting them.

The unit puts the GPS chipset into a "standby" mode between transmissions to save battery power. In this standby mode the Real Time Clock still runs and the ephemeris and almanac data are retained. As a result, after a shut off of only 10 minutes, the restart is what is known in the GPS world as a "hot start", and assuming the GPS signal strengths are at all trackable, it re-acquires them in about 1 - 5 seconds.

But, since the GPS chipset is in standby between the track-mode transmissions, it might be up-to 10 minutes before it "notices" that there's no GPS signal anymore and blinks the LEDs out of sync. So, what you observed is normal.

Speaking of parking garages: Really interesting note: In the New Orleans Airport's parking garage, they've implimented some sort of broad-band passive repeater system, apparently to make XM and Sirius radios work. This passive system also allows GPS units to work and allows the SPoT to transmit out! My SPoT works anywhere inside the New Orleans Airport parking garage (including lower floors, near the center of the structure) almost like being in the clear outdoors for both GPS reception and transmission!! Floored me when I first discovered it. (My several-year-old, not-very-sensitive Garmin Nav unit works fine in this garage too!)

I'm treading dangerously close to reveling some trade secrets here, so please understand, if my answer seems evasive, its to protect trade secrets and keep me from getting fired for being more specific...

But: depending on many variables and metrics, the unit does "track" certain metrics that give it "confidence" in the GPS accuracy. If it sees a down-tick in overall confidence, it usually will wait up to a few seconds for the confidence to get better (many variables in the algorithm). So, the situation you described, in simplified terms, would usually postpone the transmission for a few seconds.

Rest assured, however, if it has a fix at all, it has "bail out" criteria that will transmit whatever it has eventually (well within the 10 minute window between messages in Track mode or the 5 minute window in 911 or Help modes) even if the various "confidence criteria" metrics are failing to settle down.

If it is "time to report" (10 minute interval in track, 5 minute in 911 or help), and it gets a fix, and just before it transmits the GPS signals disappear entirely, it will wait a few seconds, then if the signals don't return, it will transmit the last GPS co-ordinates it had.

When Budweiser and Miller are the only choices, I order Coke or Sprite.

I’ve been following this thread for a while now while I try to decide if I should get a spot unit for an upcoming trip to <?xml:namespace prefix = st1 ns = "urn:schemas-microsoft-comffice:smarttags" /><st1lace w:st="on">South America</st1lace>. A lot of really good information here.

What does the simplex modem data coverage have to do with the usability of the spot unit. If you look at the findmespot site its coverage area is much larger.
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http://www.findmespot.com/ExploreSPOT/Coverage.aspx

-Jeff

OK, a little thread search answers the simplex network question, but why would the two coverage maps be so different especially when you look at eastern South America.


-Jeff

The Globalstar Simplex Data Coverage map is from September 4, 2007. The SPoT coverage map is from November 1, 2007. They do represent the same system.

During the months of September and October 2007, Globalstar added simplex receiver card cages to several of their ground stations to increase simplex coverage because of the launch of SPoT! This coverage enhancement will be ongoing, but I'm not privy to the details of the schedule.

The coverage map on the SPoT website is kept up to date better than the one on Globalstar's web site. Globalstar would do well to update the one on the Globalstar site accordingly.

Spotmaker,

Your measured and in depth answers make me more confident in the SPoT than any survival man's commercials. Many thanks, I never had such substantial feedback from a pro in eigth years as a GPS user. And thanks to the members of this forum for keeping up the dialogue.

One of my sons wants to go on a motor bike tour on back country roads through eastern Europe down to the Balkans after high school (with zero experience in biking). He won't take arguments since he knows that I went on a Vespa from Sweden to Marrakech and back in 1967.

I've been doing things years back when I knew I risked my life should my catamaran capsize or have a hull destroyed by impact. My sons will take risks, and so will other young men. SPoT will help some of them survive and help them sort out problems underway. Most of them won't have the patience to learn the Zen of SPoT use by themselves (With reference to the book 'Zen and the art of motor cycle maintainance').

You mentioned:

'If it is "time to report" (10 minute interval in track, 5 minute in 911 or help), and it gets a fix, and just before it transmits the GPS signals disappear entirely, it will wait a few seconds, then if the signals don't return, it will transmit the last GPS co-ordinates it had'.

I actually saw the tracking LED light up for five seconds in that garage after ten minutes had elapsed but thought it too weird to be reported. Your answer explained why it would happen.


You mentioned:

'Interestingly, GPS gain is biased slightly in the direction of the buttons and LED's, which means GPS sensitivity is rather crappy on your belt.'

So there must have been some other reason why the antenna was not rotated 180 degrees...

Edit/add: I just made a test sending help messages while walking in a tall beech forest. No leaves yet. Out of eight transmissions, only one was received and that one occured at an opening towards SW in the forest. The LEDs indicated a GPS fix all the time and transmissions occured at regular five minutes intervals. It seems that trees seriously impair transmissions. It could be that moving adds to the difficulties. This means that tracking won't work in a forest either even if you hold the device horisontally and away from the body all the time, at least not when you are above 40 degrees latitude (I'm now at 50). Most sats will then be way below zenith and transmissions thus have to travel through a maze of twigs and branches even if the eye mostly sees sky through the crowns of the trees. The rule of thumb seems to be that there can be no trees above x degrees from zenith were x is the latitude that you are on.

If simplex transmissions occur only once as indicated by the solide LED light then it would easily happen that some bits are lost and the message thus discarded. This appears to be an inherent weakness of sat simplex uplinking, which was probably not designed for this task. Isn't there any cacheing of the signal such as for sat radio? One would believe that redundancy was built into the system. When driving along coastal roads on Vancouver Island recently, I was impressed of how little interruptions occured on Sirius radio inspite of the tall, dense forest on both sides of the road. But then sat radio has a lot of redundancy built in to handle short interruptions in data transmission.

Thanks for the update on increased simplex coverage. It was reported in a swedish forum that a SPoT worked fine over easter during a ski trek in northernmost Sweden at 68 N, 18 E. Two OK messages were sent per day during a week, all received. According to the Global Star coverage map, that would be at the fringe of the fringe, but not according to the SPoT site map. So it is possible that the Global Star terrestrial gateway in France has been upgraded as well.

Another SPoT user reported being helped when his snowmobile broke down, but that was only at 64 N.

Re transponders: Sirius and XM transmit at 2.3 GHz. The reason why transponders in an airport parking building would be so broadband as to include both GPS at 1572 MHz and even allow SPoT transmission at 1630 MHz must be that they are intended to let GSP users get a fix and let cell phone users use their phones at 1900 MHz. I'm glad they now provide this kind of service. I still remember coming out of the garage at Orlando airport in a rental car and having to enter traffic flow before I had a GPS fix. Amazing that the transponders you mention work so well even for dual mode.

Regards,

Jonas

Website item:

May I join with others to emphasize that we want to be able to log in to messages on the findmespot site with a (java enabled) mobile phone or bluetooth linked PDA.

A long range digital 450 MHz cell phone system is implemented in Northern Sweden, Norway and Finland. It won't cover all of the wilderness in the mountains bordering Norway. But still, for anyone setting out to help a SPoT user, cell phone accessability to messages is important. The helper could have a satellite phone also for that matter.

I can read gmail with mailed SPoT messages on the cell phone and paste coordinates to Google Maps, but I can't access tracking. So we're waiting for http://mobile.findmespot.com/login...

Moving, in and of itself, is not a problem. I and many others use the SPoT in track mode in vehicles, and on motorcycles while at interstate speeds.

Foliage is an attenuator, motion combined with obstacles like foliage can produce random RF fading patterns, but in reality, these patterns can help as much as they hurt, actually. Motion combined with obstacles typically turns out to be a wash.

Just how much foliage attenuates the signal varies, of course with the density of the foliage, how wet it is, even the type of trees involved.

In general, even under rather deep forest canopy, if the unit is placed face up, a few messages ought to make it through. This is why in 911 mode, it transmits every 5 minutes forever. So, even if only one message is making it through the canopy every couple of hours, messages still get out.

In track mode under thick canopy, 10 - 20 percent is typical. On a trail where some sky is visible, it will be much better.

Track mode messages, under ideal clear sky conditions, give you somewhere from 70 - 90 percent success rate, depending on exactly where you are in the coverage area.

The check in messages are sent with triple redundancy. Three messages are sent over a randomized interval lasting between 10 and 20 minutes. Due to the fact that the view of the satellites is constantly changing, this results in a success rate for check in messages better than 99% under a clear sky, in the "dark orange" areas of the coverage map.

As I mentioned, there wasn't any foliage, but still no messages went through while on a road in the forest. More than 10-12 meter high trees though. A total of about ten messages were sent (help + cancel help). It could be that it is more difficult to get messages through if you at high altitudes and far away from the ground station.

For phone service, I believe Global Star mentions that there can be contact with three different sats at the same time, with a synergetic effect. Is this the case with simplex traffic also?

Before, I kept my SPOT inside my tank bag, right under the cover. Then, from other user´s input, I started carrying it in my camelback. I don´t have it face-up. It's just laying, alone, in the pocket.

When I tested it, in Wisconsin, and it worked perfectly, I had it face-up on the dash of my truck.

I really like the technical explanations and experiences. I don't understand it, but I like it.

If I'm in South America, I should try to find a dedicated mounting location so that it can always be face-up? The best place I can think of is on top of my top case, but that exposes it to theft. Especially since, every time I stop, this huge BMW is like a kid-magnet, and nobody respects anything. Everyone is touching everything all the time. And if it's not in my line of sight, and not nailed down, it'll disapear.

One of the guys at SPoT Inc. wedged his SPoT in between the bottom of the window frame and the sliding shade in the window of a 767 or 777 (I forget which specific aircraft type), with explicit permission from the Capitan of the flight (strictly speaking, you're not supposed to use one on a commercial aircraft) on a flight from LA to Boston. It was wedged with the "face" of the unit against the window glass. He got results that were almost too good to be believed (but I saw the track with my own eyes). It was something like 28 out of 30 messages. So, altitude doesn't hurt.

I've also been following some BBS posts by private pilots who have SPoTs mounted on the dash of the cockpit of small planes. They also report results, flying around North America, of around 90%. So, in a plane, with a decent view of the sky, actually seems to work slightly better than on the ground.

Yes.

Bananaman,

The unit should be kept horisontally with the logo side facing up. The antenna is directional for both GPS and sat uplink. It is not like a cell phone.

Spotman,

Re transmissions through "winter canopy":

Sorry, I wrote high altitudes where I should have written latitudes, my thought being that since the SPoT in that situation has to communicate with Global Star satellites which are low on the sky (low elevations), the signal usually would have to go further down from Zenith and thus be more prone to be scattered through trees. I know that my old Garmin ique 3600 will not get a fix when walking in a forest, not even in winter, whereas a SiRF III receiver easily gets and maintains it. For transmission it should be worse.

The image attached below I found on the web. This is the kind of winter canopy I'm talking about, minus the frost. You'll get a fix but few messages would come through. Thus, conditions are asymmetrical when it comes to receiving versus transmitting. The risk would lie in the false presumption that transmissions work since there is a GPS fix. When leaves are out, the user would be alerted to the propagation difficulties by the lack of a GPS signal.

Even if no HELp messages transmitted during walking could be received when I tried, it is quite possible that messages would have been received if the unit had been left immobile in one location. Haven't tested that yet.

With a PLB, transmisssions can either be picked up by four LEO satellites or by geostationary ones. At high latitudes, geaostationary satellites are seen at low elevations. The geostationary Astra satellite (TV) is seen 26 degrees over the horizon in southern Sweden. At such elevations trees can be a great problem. At high latitudes,PLBs would therefore have to rely on the LEO satellites. Since they are in polar orbits, they would sometimes be directly overhead minimizing canopy problems. But "sometimes" could be rare occasions. And one can't be sure that transmission would occur at the moment when the satellite is overhead. So the PLB appears to suffer from the same limitations when it comes to transmission through canopy. You just can't be sure. Well, that's OK as long as I realize the impact of surroundings.

The circular polarization and DSSS modulation used by Globalstar's simplex system are fairly robust against polarity shifts and reflections.

I've used my SPoT under exactly that sort of winter canopy, and was still getting around 50% throughput.

Of course, it's true that any obstructions to the sky will degrade performance, so YMMV.

I've found that two environments that look similar to my eyeballs can oftentimes have very different effects on the SPoT's performance (one similar looking environment might hurt its performance much more than another).

I've found that just what environment is going to screw it up the worst is often hard to predict. "Urban Canyon" environments can really be crazy, bad, and unpredictable. Trying to use it in the downtown area of a city will usually be disappointing.

Correct me if I'm wrong, but don't PLBs transmit more-or-less continuously until their batteries die (a day or two)? At high latitudes at least one of the LEO satellites should appear well above the horizon in short order (a few hours). In any event, several satellite passes may be required to locate a non-GPS enabled PLB, so a SARSAT position fix may take a significant amount of time in some cases.

In addition, transmitting 5 watts at 406 mHz gives PLBs more than 10 dB transmitter gain over SPoT and probably a lot less path loss due to foliage and path length. In other words, they should be less dependent on an unobstructed view of the sky (provided any obstructions aren't made of rock).

I continue to be impressed with my own SPoT experience. It's not a PLB (and wasn't designed to be), but it works very well in its intended use.

Cheers.