Spot Messenger 2: thumbs down

[ILUVSWTAS]

Good review Ninja, and your obviously someone who we should listen to having all 3 units.

[Nuts]

You seem to have an interest in the negatives here SWT..

I can't say ive ever set off our Spot in an emergency nor the PLB.. I would add (having used a satphone on a daily basis) that they arent perfect either. Whole days, clear sky, clear view, no signal
I do prefer the 'idea' of two way communication as the way for the future.

Spot customer service has been dismal, almost as frustrating as telstra. Haven't had to contact any of the PLB companies so far...

[tasadam]

Re the chopper not finding you quicker with the PLB incident, I think that could be a fair question for SAR to be asked - it is in our interests to know what sort of problems they encounter - was it inaccurate data from the PLB? Are there certain anomalies in getting the homing beacon thingy to work properly? Other factors that might come into play that hamper them?
The other thing, I thought the PLB kept transmitting, so if the signal improved, they would get better "intel".
Course, anything found out can be added to this topic - viewtopic.php?f=21&t=3911&p=44377#p44377
Take note of some of the tips there already, eg placing the PLB on a space blanket shiny side up to help the signal...

[ILUVSWTAS]

You seem to have an interest in the negatives here SWT..

Eh? I was just saying Ninja puppet has all 3 units, so he is probably in the best position out of all of us to make an educated report... ??

[South_Aussie_Hiker]

Re the chopper not finding you quicker with the PLB incident, I think that could be a fair question for SAR to be asked - it is in our interests to know what sort of problems they encounter - was it inaccurate data from the PLB? Are there certain anomalies in getting the homing beacon thingy to work properly? Other factors that might come into play that hamper them?
The other thing, I thought the PLB kept transmitting, so if the signal improved, they would get better "intel".

The homing signal is just another radio signal; useless if the searchers don't have a directional antenna to pick it up.

AFAIK a PLB without GPS can mean a search radius of a km or more cp. with GPS which can get it down to metres.

just to add, I dont know whats it with that homing device on the PLB, but it certainly didnt work for us. not sure if its because our SAR chopper didnt have the device to detect the homing signal, or if the signal is weak, but hearing a chopper hovering around nearly 3 hours looking for us made us very very nervous.

I think what you are talking about here is the 121.5 Mhz homing signal which is on some PLB units (non GPS).

The 121.5Mhz signal is in the range of any normal aircraft VHF radio, so the helicopter can most definitely receive this. The procedure for locating a beacon using the 121.5 signal can be time consuming. The process involves flying a line to find the point of strongest signal strength, and then turning 90 degrees to this line and starting a new line (if it gets weaker, you've turned the wrong way and do a 180 turn). Once this has been done once or twice and the beacon is closer, then the radio is detuned (for example to 121.475) which decreases the sensitivity of the radio - and the procedure is repeated.

It is a bit of a time consuming procedure, but doesn't take 2 hours 50 mins. The chopper taking so long was probably a result of the incorrect GPS position - as these are generally very, very accurate the crew would have trusted this over completing a homing search procedure.

As for the inaccurate GPS position, that's just what happens. People have an assumption that a GPS position is always accurate and can be obtained very quickly. Aviation spec GPS systems can still take a long time to obtain accurate position information - and they have complicated barometric altitude inputs, integrity monitoring and can selectively exclude satellites which appear to be providing poor fixes or which are very low on the horizon and reducing accuracy.

I believe the theory with modern PLB is the 121.5 signal (where fitted) is in fact quite weak - this means that the homing procedure can be completed more quickly and accurately.

Old 121.5/243 beacons transmitted a very strong signal (because initial position was not provided by satellites) and this meant the homing procedure was much more time consuming and less accurate.

[Nuts]

You seem to have an interest in the negatives here SWT..

Eh? I was just saying Ninja puppet has all 3 units, so he is probably in the best position out of all of us to make an educated report... ??

I probably should have used this , sounded like you had (or had heard of) a bad experience..

A lot of single events don't mean a great deal with these devices (seems to me) my main thought is that two way comms are the go. As its a topic about spot and reliability that thought is probably a bit off the topic. These things do move so fas though.. the new satphones caught my eye: http://iridium9575.net.au/ (for adams / the emergency devices link perhaps)... cost a small fortune but how 'safe' (or in touch) does 'one' need.

Anyhow.. I have the three options (mentioned so far) sitting here... trying to decide between them for an upcoming walk..

[Ent]

Hi

Interested in the homing signal issue of the PLB units. In another thread about been up another creek without a paddle a Spot was successfully used but the helicopter pilot that time made reference that there was no signal to home in on. Also I believe due to the backup helicopter being used range and time over the search area was a concern. The group did make it to high ground so the pilot could make a visual confirmation without any difficulty. The homing method described sounds similar to radio landing approach and I would imagine that a dedicated search and rescue helicopter might be fitted with a direction antenna but of course the crew might have been "victims" of GPS is always right belief. Does suggest though a few dollars more spent on a GPS equipped PLB not a bad idea. GPS signal positions in steep valleys can be very suspect though. For an helicopter rescue it would not matter much which side of the river but for ground rescue it would be much more difficult, not to mention annoying finding yourself on the wrong side of a raging river and many hours of back tracking required.

Interesting point Nuts. So at home central the "control room" would be on standby to interpret a non moving signal as "come an get me" as opposed to "found a great camping spot and need a rest" Also as time plays a big part if a search is a rescue or recovery exercise, so when does home base hit panic stations? Still for those that walk solo that will become incapacitated and unable to press a button it would be handy but not too sure how often such events happen Sounds like plan A of walking with someone else night be the go

Actually yet again we are spending a lot of money based on trust and limited knowledge. I wonder how many rescue beacons do not work or have issues limiting the ability of search and rescue to get to the position, say flat battery, broken unit, etc. Actually battery life is an issue and I am somewhat surprise that Spot 2 went from the AA used in Spot 1 to AAA so reduced the expected life down to 1/3 on what would have been achievable. Space and weight again played a part no doubt.

We know that not all GPSs are created equal so not a stretch to apply this to GPS equipped rescue beacons. Sadly S&R has not taken the leading brands to a known or suspect tricky locations and evaluated which one works the best. Until then we are rather (again) victims to assumptions

Oh and for the record I have the same PLB as Tasadam got from the same shop as well. I found evaluating rescue beacons near impossible so went with one with an inbuilt GPS. Hope I made the right choice

Cheers

[Nuts]

Interesting point Nuts. So at home central the "control room" would be on standby to interpret a non moving signal as "come an get me" as opposed to "found a great camping spot and need a rest" Also as time plays a big part if a search is a rescue or recovery exercise, so when does home base hit panic stations? Still for those that walk solo that will become incapacitated and unable to press a button it would be handy
Cheers

Exactly They would know what to expect and something wasn't right. If (at the allocated time) the beacon still wasnt moving they would at least know whetre you were. This, even assuming that the continuously transmitting beacon hadnt been stet off or that the user messages hadn't arrived.


As mentioned in the last post, things are moving on from all these devices though. The ideal is almost reached with a beacon and tracking on a satphone. Next comes smaller/waterproof/Cheaper.

[Ent]

Hi

On phones and other electronics. I have a rather bitter experience with anything that is not water proof. Sure protective cases help but actually dew point killed my last phone and IPAQ. Lot to be said for any electronic gadget that can look after itself. The ultimate would be a locating device that you can send condition reports and receive back medical assistance advice as even with an immediate scramble S&R will be over an hour away even in a place as small as Tassie. Be nice to have medical advice available until then.

Cheers

[photohiker]

Actually yet again we are spending a lot of money based on trust and limited knowledge.

Are we really? I guess it depends on how you value your existence. Compared to a very few short years ago, we now have a bunch of options that I for one think of as cheap. We personally have a Spot and a Satphone (as well as mobile phones and uhf when car camping) and we spend less than $200 a year for the peace of mind and the chance of help and rescue they give us.

I guess I'm a glass half full kinda guy. Clearly, the tech of all these devices works to the point where it would be just plain bad luck if it didn't work for you when you needed it.

Of course the technology could be better, and the companies could fall over themselves to answer every question asked on a forum, but that all costs them $ and guess where that ultimately comes from...

I really like the idea of the spot connect and similar, those upcoming devices with two-way comms would be great in emergencies but I guess not so much day to day.

NP: With Spot, carry spare batteries and press the Ok button as much as you like.

[Nuts]

Sounds like plan A of walking with someone else night be the go

Cheers

Hi ENT

Solo with no beacon, nothing.. (edgy 'old school' thought that eh..?)

[Ent]

Actually yet again we are spending a lot of money based on trust and limited knowledge.

Are we really? I guess it depends on how you value your existence.

Um? Strange I can go to Choice and get an independent review on a toaster, vacuum cleaner, etc but not when spending a lot more money on something that might save lives or is at least sold with that message. As the thread originator suggests maybe Spot is not to be trusted getting out a signal in difficult terrain. My original reading suggests that the original Spot struggled under tree cover and as trees are rather common in Tasmania this is a worry, if those reports are correct. My comment is still valid that we are spending a lot of money based on trust and limited knowledge. The silence by the providers of Spot does not help to improve confidence but then again I wonder if the response would be any different from GME or other brand to a question on coverage of their PLB range.

It would be a tragedy if a locator beacon was triggered in a deep tree covered valley when it was known to the manufacturer that the chance of getting a signal out in that terrain was low. If you knew that then you might be more inclined to leave the distressed person and seek clearer skies and wait for S&R then lead them to the person in distress. If you knew it would work then you would stay and provide aid to the distress person. Surely we consumers deserve this information?

Regards

[photohiker]

It would be a tragedy if a locator beacon was triggered in a deep tree covered valley when it was known to the manufacturer that the chance of getting a signal out in that terrain was low. If you knew that then you might be more inclined to leave the distressed person and seek clearer skies and wait for S&R then lead them to the person in distress. If you knew it would work then you would stay and provide aid to the distress person. Surely we consumers deserve this information?

Sorry, this is just not true. We do have that information. We as consumers cannot blame Spot or any of the other location device suppliers for something that they have made clear in the packaging, the instructions included with the product when you buy it, and on their websites. People have also posted this information here based on their own experiences that confirm the manufacturer's advice.

For instance:

http://faq.findmespot.com/index.php?act ... y&data=240

SPOT is a satellite product and needs an area clear of tall obstructions to maximize message delivery success. Buildings, inside cars or planes, dense wet tree cover, mountains, caves, canyons, etc…can reduce message delivery success.
It is normal for some messages to be blocked by your environment and the reliability of SPOT is enhanced by the fact that every message type transmits multiple times during its cycle. OK messages transmit three (3) times, discarding any extras after the first is received.

SPOT is an electronic device that uses GPS as a portion of its service. Using other GPS devices and operating SPOT in areas of high interference such as airports and cellular or satellite towers can throw off the coordinate reporting and sometimes even block message transmission.

Spot strongly recommends that you send and verify an OK/Check message before using your SPOT each day, and at minimum anytime you have traveled more than 600 miles, have changed the batteries or have not used the unit for over two (2) weeks. List your own cell phone (if you have text capability) in your OK contacts.

To run the check:
1) Press the ON/OFF button
2) Wait 2 seconds
3) Press OK
4) Wait until the LED above the OK button goes off (can be up to 20 minutes).

You have now completed the GPS Fix / System Evaluation cycle. If after 4 minutes, the LEDs above the ON/ OFF and OK button start to blink out-of-synch instead of in unison, you still do not have a GPS fix. If you haven’t used your unit recently it may still be updating the almanac or it might not see the 3 GPS satellites required to obtain a GPS fix, so it is highly recommended that you MOVE to a different location with a clearer view of the sky in order to get a GPS fix, and repeat Steps 1) through 4). The LEDs above the ON/OFF and OK button should blink at the same time until they go out if you have successfully obtained a GPS fix. Optimally, you run the test in cell phone range and can ensure that your cell phone received the text message with your lat/long location.

You'll find the same sort of information on the PLB manufacturer and SatPhone service sites. Why on earth would they withhold it?

Basically, until these devices have an infallible location service that basically works under water or rock and the ability to call home via subspace communication ala Stargate/Startrek then we are just going to have to do the best with what tech is currently available.

The tragedy would be taking any of these devices into the bush and not reading or understanding the instructions.

The reason you don't read about these in Choice is because unlike toasters and vac cleaners, not that many people buy emergency locator devices be they Spot, PLB or whatever. They just don't appear on their radar because most consumers hardly even know such things exist.

[Jellybean]

+1 regarding the importance of a dose of common sense and taking responsibility for one's own actions (instead of seeking to blame those nasty manufacturers who are only out to siphon our bank accounts) . Agree too that the absence of any PLB/EPIRB review in Choice or suchlike is due to the size of consumer demand rather than the lifesaving potential of the product.

[Ent]

So we read standard disclaimers designed by lawyers as fact. Bit like my Giant XT2 mountain bike that makes great store of its racing heritage and then has a lawyer written declaimer buried deep in the documentation that the warranty if void if used in a race I am not after legal fine print and disclaimers but facts on what is the more reliable system. They do not exist or more accurately I can not find them. As based on user reports I would suggest that Spot appears rather suspect but then unhappy people tend to be more vocal than happy ones. Also with a PLB you have no ideas how it performs until you push the button so have no way of testing beforehand if it is a better system, while Spot can be evaluated with the tracking option.

You have two competing systems yet we have no clear idea which works better in getting out a distress message. That is the simple and unavoidable fact and quoting manuals does not answer this straightforward question. I have been watching and reading reports on locator beacon rescues trying to piece together what works better. Two reports on this site appar to conflict on the usefulness of the homing function of a PLB

If both systems are similar in their reliability then by all means compare and contrast the niceties such as what colours do they come in but if say one is vastly superior in getting a signal out then I would be prepared to trade niceties for certainty. With the Spot you can monitor the track and yes I have briefly used one and noticed missed call home signals and a plot that put it someway away from were I was at times plus missing tracking plots. I have spoken to teachers that use one with their school groups and they find it needs a view of the sky clear of trees to be reliable. Not so easy in Tasmania but if you live in a plce with few trees then maybe not such an issue I put such missed signals down with my use to my unfamiliarity with the unit but it appears that it might be a weakness of the system.

Surely we consumer deserve to know simple facts like pick up time based on angle of sky visible and the power and frequency of the unit resulting in its ability to punch through tree cover. Historical success to failure ratios and under what conditions the failures happen. I struggle with the concept that it is my fault for not been able to compare and contrast the systems but that is a common theme of some peoples posts along with read the manuals throw away lines. Yes I have read them Also I spent a lot of time as a kid around Amateur Radio Operators that would build and modify radio equipment so understand some of the basics of radio communication. In fact as I write this I am listening to a CD that is going through an amplifier that I built myself to a pair of electrostatic speakers that I built so have some idea of electronics

Also in an emergency people are under stress and may not be able to climb to a position that has a no obstruction of the sky. Indeed trapped in a steep valley is not uncommon, at least in places that it rains a bit. In fact site users would be well advise to stay away from river valleys based on two/three reports featured on this site I would love to say the X system is ten times more likely to work in those situations but a can not. But coverage of satellites (orbits might be optimised to cover the USA not Australia and especially far south as Tasmania) along with frequency used, unit power and low versus high orbit will play a role. I not having a PHD in satellite communication can not process this data and make a definitive statement. All I can do is infer for my own purchasing decision that a PLB system to me appears potentially more reliable but that is a non technical belief rather than a statement of fact. I would love to see peer reviewed research that would confirm or disprove my belief. Is that now where I copy in large chunks of my PLB manual to make it appear that I understand satellite communication?

No my original comment stands. We are spending a significant amount of money based on trust and uncertainty. We demand standards to compare sleeping bags, car fuel consumption but with devices that get sold based on safety reasons we have silence from the sellers. But by the looks of it growing number of disclaimers. I wonder if the next one will be "this is not a rescue device" similar to what appears on kids pool toys. In fact locater beacons are mandated by law for certain situations. Therefore they should have clear standards of reliability and means for customers to determine performance. Is it worthwhile carrying a bigger unit that has a more effective aerial or is the likely difference in real life minimal?

Oh yes thanks for your rather typical trivialisation of the matter with reference to subspace systems. And for the record even in Star Trek when the crew are trapped under ground the communicators do not work, at least in some episodes

Regards

[photohiker]

Oh yes thanks for your rather typical trivialisation of the matter with reference to subspace systems.

Welcome back Brett.

You'll get along with me a lot better if you refrain from personal criticism.

The reference to subspace was a humorous indication that the perfect device does not yet exist.

Spot vs PLB vs X. Your choice. the info is out there, all you have to do is look and choose. Heck, buy all of them.

As far as manufacturers printing certainties about when and where their products will definitely work? Good luck! They will have a risk assessment team of highly qualified legal personnel pore over and sanitise every statement or claim that is for public consumption. This is the counter intelligence required to protect the business from rampant legal damage actions based on trivia. Its like a disease in the US and getting worse here all the time.

[andrewbish]

Hmmm. Sounds like the gist of this is that Spot need to make a better device and until then we need to be wary of over-reliance on these things. I actually just bought a Spot in prep for a longer than usual solo hike next week. As I have mentioned elsewhere in the forum I like the ability to send a 'call off the calvary' message when a previously dire situation improves to the point where rescue is not required - That way I can (1) save someone some money somewhere in the system and (2) avoid the embarrassment of an unnecessary rescue! I really get it in regard to manufacturers needing to produce stuff that works when we need it to. From what I can gather from this and similar threads, no PLB or PLB-like device is infallible.

Excuse me while I cr@p on for a minute:

You guys would prob consider me reckless, but I actually crave the risk that the back country offers. I spend most of my time in the uber-safe, 'bubble-wrapped' world where adventure, risk and danger is discouraged. For years I have blissfully gone along with this like one of those drip-fed automatons in the Matrix movie. I need cold, the precipice, the snake to remind me that I am alive. I don't expect Spot to save me if TSHTF. That responsibility rests mostly with me and to be honest, I felt a bit lame getting a beacon at all - if feels like a step backwards, towards the couch and the tv. Before we had this technology men (and women) didn't hesitate to head into the mountains. Why would they? They measured the risk, planned their mitigations, such as they could...and then got on with it. And so should we.

Let's keep encouraging the PLB manufacturers to make better products; but let's not spend too much time worrying about them (and the leeches - I mean lawyers - they engage) - let's get out there in the wilds.

Andrew

[sthughes]

Of course people actually use Spots, where as PLB's are hardly ever activated in a lifetime of service. When there are barely any instances of PLB's even being activated in the first place is it any wonder there are a lot more instances of a Spots "failing" than PLBs "failing" ?

[Ent]

Of course people actually use Spots, where as PLB's are hardly ever activated in a lifetime of service. When there are barely any instances of PLB's even being activated in the first place is it any wonder there are a lot more instances of a Spots "failing" than PLBs "failing" ?

My exact point. We do not know. Spot does rather set itself up to fail while PLBs remains largely unused so can not be tested until needed.

Might be to get on my right side Photohiker you should accept my comment that "we do not know and rely on trust" or point me to a source where I can compare and contrast the systems based on a comprehensive review I assume you do not joke about carrying a bomb when going through airport security? Maybe some things like safety devices need a bit more considered response

It might be a fair comment that people at the moment largely consider the performance of the two system comparable. Based in missed way points and call in signals experienced by Spot owners it appears rather dubious on reliability but then so may be PLBs. Surely we should be given better advice. Rather tired of lawyer proof answers that are sanitised and spun by marketing types or stony silence where the honest answer would give the game away. Would your choice be influenced if one system was ten times more reliable than the other? I know it would be for me.

As for the rugged outdoors, yes we take risks and good on us but I would like to think that we are sensible with our risk moderation strategy otherwise it is suicide by bushwalking. I walk with a group that has ages spanning from one to seven decades so would like to have the best means to get help ranging from lost party member to a medical emergency. Actually have not desire to use the locator beacon as an excuse to "push the boundaries". Just want it there if injury or medical issue crops up. And then I want it to work or know when it likely will not work. Yes relying on it for a caving expeditions is rather ambitious if not foolhardy but steep dense valleys are rather common terrain, at least in Tasmania, so that is where my interest in reliability comes from. Actually lack of feedback if a message gets out is a worry and one that I hope future locator beacons correct with acknowledging that the message got out.

Regards

[photohiker]

Might be to get on my right side Photohiker you should accept my comment

Sorry Brett, I did not realise that I was on your 'wrong' side, and no, I do not accept your comment even if it leaves me there.

This is the internet, we are free to disagree, I am suggesting that you leave the personal criticisms alone.

Play the ball not the man.

[Dale]

You guys would prob consider me reckless, but I actually crave the risk that the back country offers. I spend most of my time in the uber-safe, 'bubble-wrapped' world where adventure, risk and danger is discouraged. For years I have blissfully gone along with this like one of those drip-fed automatons in the Matrix movie. I need cold, the precipice, the snake to remind me that I am alive. I don't expect Spot to save me if TSHTF. That responsibility rests mostly with me and to be honest, I felt a bit lame getting a beacon at all - if feels like a step backwards, towards the couch and the tv. Before we had this technology men (and women) didn't hesitate to head into the mountains. Why would they? They measured the risk, planned their mitigations, such as they could...and then got on with it. And so should we.

I can relate to that Andrew. So has Bushwalking become the new 'Fight Club' ?

[Ent]

Maybe it is I have spent too long in safety meetings or seen the distress up front of bad events cutting short lives along with the after effect on others but safety is not an issue to be trivialised for me as it diverts attention away from the key issues. I am looking for what is the respective reliability of the systems though Spot does appear to be increasingly coming under scrutiny on more than a few forums. Are the same concerns valid with the alternative PLB?

Subspace communication and flights of fantasy rather adds nothing to this thread. But if that is where it is to head then it is easy enough for me to avoid the thread and allow others their internet "right" to shred the thread and then claim personal insult when I mention this is a distraction.

Anyway enough said and thanks to the original poster raising his concerns. If anyone can help out with valid information on what is the potential reliability of the locator systems and what to expect when used in steep valleys please PM me.

Thanks.

[andrewbish]

You might be onto something there, Dale - not that I particularly want to hit anyone!

It is fair to say that we all have different appetites for risk. I tend to seek it out and make it part of my walking in some way; others take a more measured approach and prefer risk to be more contained - focussing instead on other elements of the bushwalking experience. It's all good and I don't think there's a black and white to this.

Anyway, off the therapy couch and back to the topic! I will give my new Spot a workout around Bogong this weekend and report back.

Andrew

[tasadam]

If anyone can help out with valid information on what is the potential reliability of the locator systems and what to expect when used in steep valleys please PM me.

Thanks.

Additionally / alternatively, you are welcome to post your comments and opinions here on the forum. Well, within forum rules anyhow. (Perhaps we'd all like to know?)

[Ent]

Additionally / alternatively, you are welcome to post your comments and opinions here on the forum. Well, within forum rules anyhow. (Perhaps we'd all like to know?)

Very valid point tasadam

It is very difficult to get information on the merits of various systems but here is a few interesting bits that get scattered around the web. I have included links so people can let me know if the comments are, solid or rather lax in factual basis as the internet is not renown for reliable information.

First how a PLB was decided if it was a good or a bad thing. http://www.sarsat.noaa.gov/emerbcns.html

Prior to July 1st, 2003 only residents of Alaska had been able to use PLBs. The Alaska PLB Program was set up to test the capabilities of PLBs and their potential impact on SAR resources. Since March of 1995, the experiment proved very successful and helped save nearly 400 lives while generating only a few false alerts. The success of the Alaska PLB program undoubtedly paved the way for nationwide usage of these devices.

Hopefully this will put paid to the doubts that PLBs are useful. In one state of the USA there are 400 very happy family and friends that the person that they cared about had a PLB Interesting the length of the study I thought it might have been much shorter given the impact it had on lives saved

Next lets look at system that many might have been considered ok as it was even a mandated device. Please no angst here as it is now a defunct system so not attacking a current system http://www.sarsat.noaa.gov/emerbcns.html

Different types of ELTs (Electronic locator transmitters) are currently in use. There are approximately 170,000 of the older generation 121.5 MHz ELTs in service. Unfortunately, these have proven to be highly ineffective. They have a 97% false alarm rate, activate properly in only 12% of crashes, and provide no identification data. In order to fix this problem 406 MHz ELTs were developed to work specifically with the Cospas-Sarsat system. These ELTs dramatically reduce the false alert impact on SAR resources, have a higher accident survivability success rate, and decrease the time required to reach accident victims by an average of 6 hours.

Ok these are specialised devices for aviation and you have impact consideration as the newer units appear to be built to a better standard but note the faster locating time. It does explain why the old system was phased out in 2009. With a PLB the authorities know the unit number and if registered (should be mandatory) can track down the owner. So if two or more PLBs are set off they know it is two or more rather than one. Helpful with multiple parties in distress in close proximity.

Ok now the stuff that some might get upset with. Please note I am not and expert in satellite communication so there might be additional tricks to overcome apparent deficiencies of a system.

First what we bushwalkers will likely carry, a PLB http://www.sarsat.noaa.gov/emerbcns.html

PLBs are portable units that operate much the same as EPIRBs or ELTs. These beacons are designed to be carried by an individual person instead of on a boat or aircraft. Unlike ELTs and some EPIRBs, they can only be activated manually and operate exclusively on 406 MHz. And like EPIRBs and ELTs all PLBs also have a built-in, low-power homing beacon that transmits on 121.5 MHz. This allows rescue forces to home in on a beacon once the 406 MHz satellite system has gotten them "in the ballpark" (about 2-3 miles).Some newer PLBs also allow GPS units to be integrated into the distress signal. This GPS-encoded position dramatically improves the location accuracy down to the 100-meter level…that’s roughly the size of a football field!

Ok this means it is worthwhile spending the extra on GPS equipped ones even only to make life easier for S&R. However, someone on this site might not agree as GPS location accuracy suffers in steep valleys. If anyone is in S&R in Tasmania or elsewhere are you equipped with directional finding equipment and if so do you use it if you have a GPS fix and how effective is it in time and reliability?

One constant with radio communication is power improves range and ability to break through some obstacles like wet trees. If locked in a solid metal box or underground then increased transmission power will have little if any effect but if outside the more power the better the chance of a message getting out all other things been equal

So what is the transmit power of a rather common PLB the MT410G (GPS) GME PLB http://www.triginstruments.co.nz/catalo ... cts_id=874

VHF: 121.5 MHz, 50 mW ±3 dB, swept tone AM
UHF: 406.028 MHz, 5 W ± 2 dB, PSK (digital)

The critical one is the UHF 5 watt one as the VHF is deliberately low power as it is intended for close in fine tuning location.

Ok lets look at a SPOT 2 http://www.software-maps.com/spot-satel ... senger.htm

Transmission Power: 0.16 Watts

This means based on raw power the PLB is 31 times more powerful. I do remember seeing SPOT (one or two?) listed at 0.4 Watts but can not find this. Ok power is not everything as aerial design and sensitivity of the intended receivers can compensate plus a few other technical tricks that I can not even pretend to understand. But worth reading this link as it gives good guidelines of what to watch for when using a Spot 2

Here are some important tips in using your SPOT device:

SPOT needs a clear view of the sky to obtain a GPS signal and provide the most accurate location information. It is not reliable indoors, in a cave, or in very dense woods.
Orienting the SPOT device so that the SPOT logo is facing up toward the sky will improve performance as the antenna is located under the logo.
Keep your SPOT at least 12 inches away from other SPOT devices.

Note the reference to dense woods. Probably not an issue in a barren state but in my home state of Tasmania rather common especially if in valleys. This view is supported by http://en.wikipedia.org/wiki/Distress_radiobeacon

but it does not work in as many places as 406 MHz PLBs – for instance under dense forest canopy or steep canyons.

Another factor of getting a message out is frequency. Generally the lower the frequency the more a signal can bounce or curve around obstacles. The extreme is Very Low Frequency that the USN used for contacting a submarine under water. This was a system relying on extremely long aerials so not practical for a compact unit. But for transmitting under another form of water, snow, if covered by an avalanche a lower frequency is used than either by the PLB or SPOT system.

Here is a useful look at SPOT. PLB and avalanche transmitters. http://www.rockymountainrescue.org/about_PLBs.php

PLBs and SPOTs are not avalanche transceivers or beacons. Avalanche transceivers transmit and receive on a completely different frequency (457 KHz) and are typically received by similar units, carried by companions, less than 100 meters away. This frequency transmits well through snow, unlike the PLB or SPOT transmissions. Avalanche transceivers are intended to facilitate the rapid location by a nearby companion of a person who has been trapped under snow in an avalanche. Avalanche transceivers do not transmit to satellites. PLBs and SPOTs do not transmit well through snow and are not received by other PLBs or SPOTs. Avalanche transceivers are valuable and potentially life saving devices for people traveling through areas where avalanches are possible.

I am not sure in Australia if S&R can monitor avalanche transmitters but looks like if you thing is playing in snow then something to research. Note the clear warning that both the SPOT and PLB systems to not work well, if at all, when buried under snow.

Ok what is the frequency used by the Spot system. http://www.rockymountainrescue.org/about_PLBs.php

The SPOT system uses a higher frequency (1610 MHz) to communicate with its RCC, which is operated by Globalstar (a NASDAQ-listed for-profit company). The SPOT does have a GPS, but does not transmit a homing signal on 121.5 MHz. While the 5 watt 406 MHz signal used by PLBs can be used to get an approximate location (within 2-3 miles), the SPOTs 1610 MHz signal is transmitted at weaker power and cannot be used for an approximate position. Therefore, in emergency communication, the SPOT relies solely upon the GPS for transmitting location information.

Now I have no professional qualifications to claim if 406 MHz offers any advantage of 1610 MHz in getting a signal out of a tricky location. That is where I would appreciate someone to point me to a valid reference. The 1610 MHz frequency was simply chosen as it was already used for satellite phone communication by the company I believe. The 406 MHz was chosen for the PLB. Was it just because those frequency were unused at the time (or more accurately allocated) or is there some technical reason? Also if a SPOT can not get a GPS fix then it will not work. Hence, the upgraded GPS hardware in Spot 2 compared to the original.

It is difficult to establish coverage of Spot as some links claim satellite orbits are optimised for the USA with even Canada not getting as much frequency of coverage. Not sure if this is just sour grapes or Spot heritage of been a phone system so mirroring what happens with the major communication providers concentrating on the coverage in cities and not being so good in rural areas as that is where the biggest market is. When I talk of coverage I mean density of coverage the more dense the more likely a message gets out first time. Spot builds in multiple transmit feature to offset this issue. It does not cover everywhere but then again based on coverage maps it does cover just about everywhere where S&R is likely to exist. The PLB is claimed to be a worldwide system with polar satellites to overcome the usual coverage difficulties associated with geosynchronous satellites. These polar orbit satellites are designed to improve coverage to places like Tasmania and lower down. Also in the East/West valleys. How effective this is in real life emergencies I have no idea

The above suggests, but does not state, nor proves that PLB is a more reliable system for difficult locations, but it did form a large part of my decision making. It does suggest based on transmission power that a PLB should be better able to get a signal out under trees and in a steep valley. But PLBs work on a system that was driven in part by maritime reasons and neither of those issues apply for that segment of intended use so there might be a potential weakness in those situations.

Hope the above helps in understand some of the technical issues and likely pitfalls. As said with a PLB you can (or more accurately should) only "test" it in an emergency situation. The critical issue that I am looking for clear guidance on is it better to leave an injured team member and head to ground with a clear view of the sky or better to stay put with the distressed team member? I think the above links give strong reason for those with the Spot system to seek a clear as sky as practical. Have no idea how necessary this is with a PLB. But still makes sense if at all practical to get the clearest view of the sky before trigging a PLB. Plus been able to be visually sighted by S&R is a good idea as well. Of course there are situations where this is just not possible.

Cheers

[andrewbish]

Nice bit of research, Brett - particularly the bit about avalanche transmitters.

[rsser]

Good rundown.

From memory, a PLB signal goes to Cospas-sarsat which is a mix of low and high earth orbiting sats. Spot transmits to Globalstar as mentioned which is a LEO constellation; hence the importance of a clear view of the sky. (Ditto with Iridium satphones).

5w is a gov't imposed limit on UHF power.

[tasadam]

I think the above links give strong reason for those with the Spot system to seek a clear as sky as practical. Have no idea how necessary this is with a PLB. But still makes sense if at all practical to get the clearest view of the sky before trigging a PLB. Plus been able to be visually sighted by S&R is a good idea as well. Of course there are situations where this is just not possible.

My understanding is that a PLB will continue to send its location, so if I needed to activate a PLB, I would be doing it first, then seek nearby higher ground if practical.
Better to get them on their way ASAP than waste what could be valuable time looking for higher ground. Remember the bit about placing it on a FLAT metallic reflector of sorts to assist it as linked in an earlier post of mine.

Some great points in that post and as already alluded to, some practical info or experiences from the rescue services would be useful.

[cams]

5w is a gov't imposed limit on UHF power.

Not really. Commercial mobile UHF radio's usually transmit up to 25W. It depends on your license. The transmit power can be set channel by channel to various levels. CB UHF is limited to 5W I think which is maybe what you're thinking of.

Comparing the 406MHz to the 1610MHz. The usual case of higher frequency = better penetration but shorter transmit distance would be applicable. Also, it would probably be worth looking at what other devices are operating close to those frequencies that could interfere with these very weak signals. It would also effect the size of the antenna needed. 1610MHz would need a significantly smaller antenna for the same efficiency.

That transmit power for the spot seems very low. We are actually planning on designing a satellite packet data modem into one of my works future products. Apparently the same one used in spot (according to the sales rep). So will be interesting to see how it performs.

[rsser]

Indeed.

Upshot when you read the countless user reports on Messenger 2 is that you should leave the OK/Check-in, Custom and Need Help running for well over 20 mins and expect that some won't be received.

Wonder what it would take for duplex capacity so a msg received confirmation could be added.