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dla
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dla
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PostTue Jun 20, 2017 3:39 pm 
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hbb wrote:
dla wrote:
SPOT has to hit a satellite that is only 800 miles up, since it does so reliably the 400mw is obviously enough.

I'm not sure if I understand how this is a selling point in the context of SPOT v. InReach.

The Globlalstar constellation that SPOT uses orbits at approximately 1400kms.

The Iridium constellation that InReach uses orbits at approximately 780kms.

With a SPOT, aren't you relying on lower transmission power to transmit a signal over a significantly longer distance?

You'd have a valid point if SPOT didn't work.

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DIYSteve
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DIYSteve
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PostWed Jun 21, 2017 8:13 am 
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dla wrote:
And all 3 work.

Sometimes. Sometimes not. Your claims are premised on the flawed premise that SPOT messages always get out. But that's not supported by the evidence that sometimes inReach works in circumstances when SPOT does not work. See, e.g., the guy who sent 6 messages from each unit and got these results:

inReach: 6 out of 6 messages successfully sent

SPOT: 1 out of 6 messages successfully sent

Source: http://www.bchw.org/Tech%20tips/Remote%20Communication%20Test.htm

dla wrote:
You'd have a valid point if SPOT didn't work.

There's ample evidence that in some circumstances inReach and PLB successfully transmit when SPOT fails to transmit. See above. Therefore, hbb has a valid point.
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hbb
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hbb
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PostWed Jun 21, 2017 9:54 am 
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dla wrote:
hbb wrote:
dla wrote:
SPOT has to hit a satellite that is only 800 miles up, since it does so reliably the 400mw is obviously enough.

I'm not sure if I understand how this is a selling point in the context of SPOT v. InReach.

The Globlalstar constellation that SPOT uses orbits at approximately 1400kms.

The Iridium constellation that InReach uses orbits at approximately 780kms.

With a SPOT, aren't you relying on lower transmission power to transmit a signal over a significantly longer distance?

You'd have a valid point if SPOT didn't work.

Now I am confused. If the altitude of the satellite constellation is irrelevant, why in the world did you bring it up earlier in the thread?
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DIYSteve
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DIYSteve
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PostWed Jun 21, 2017 10:18 am 
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hbb wrote:
Now I am confused. If the altitude of the satellite constellation is irrelevant, why in the world did you bring it up earlier in the thread?

Distance is relevant, of course, as is transmission power. See https://en.wikipedia.org/wiki/Radio_propagation:

Quote:
In free space, all electromagnetic waves (radio, light, X-rays, etc.) obey the inverse-square law which states that the power density of an electromagnetic wave is proportional to the inverse of the square of the distance. *  *  *  Doubling the distance of a receiver from a transmitter means that the power density of the radiated wave at that new location is reduced to one-quarter of its previous value.

AFAICT, dla's claims are based on the false premise that SPOT messages always successfully transmit in every circumstance where an inReach or PLB message would successfully transmit, thus SPOT's relatively weak (1/4 of inReach, 1/12 of PLB) transmission power is irrelevant. But the evidence does not support dla's major premise, and thus his minor premise claim fails.
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Tom
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Tom
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PostWed Jun 21, 2017 10:30 am 
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hbb, that was my reaction too.  This thread is bizarre, albeit entertaining.
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Kim Brown
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Kim Brown
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PostWed Jun 21, 2017 10:39 am 
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So....is SPOT worth it? Bought one a few years ago and never signed up for the service; thinking about using it this year.
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Tom
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PostWed Jun 21, 2017 10:54 am 
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Kim, only you can answer that.  My guess would be no though. clown.gif

I don't know if this has been posted.  Seems to be a good summary of pros and cons:

http://www.adventurealan.com/best-satellite-messenger-inreach-vs-spot/
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Kim Brown
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Kim Brown
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PostWed Jun 21, 2017 11:46 am 
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Thanks, I'll check that out (I meant to say above that I had NOT subscribed to the service. So it's like a bought a SPOT for no reason at all)
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Tom
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Tom
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PostWed Jun 21, 2017 11:51 am 
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The upside is it sounds like you saved yourself a few hundred clams the last few years. wink.gif
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dla
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dla
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PostWed Jun 21, 2017 8:25 pm 
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hbb wrote:
Now I am confused. If the altitude of the satellite constellation is irrelevant, why in the world did you bring it up earlier in the thread?

I guess I'm wondering why you ask? What is your goal?

I've said repeatedly that all 3 systems work - and SPOT has been tested way, way more than InReach. Since I know you have no Engineering explanation to show how SPOT is inferior, and since I  know that SPOT gives 5X the battery life of InReach, I'll conclude that SPOT works very well indeed.

I'm happy we have choices today.

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Tom
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PostWed Jun 21, 2017 8:54 pm 
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Why don't spot messages always go thru?  Is it possible transmission power might play a role in some circumstances?  If so wouldn't the higher transmission power of one make it more reliable than the other, everything else equal?
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dla
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dla
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PostWed Jun 21, 2017 9:57 pm 
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Do all InReach messages go through? (NO is the correct answer).
As I said a long time ago, transmission power is a meaningless metric - there are just too many aspects to antenna design.

I've actually tested SPOT's ability to hit a satellite - have you? I've found the level of foilage at which the signal won't get through - its pretty dense. Many people don't know the different message types and don't understand the two radios in SPOT, so they think a "lost"  OK or TRACK message means an SOS wouldn't get out.

But the fact remains that SPOT works, as does InReach. They should be measured by the value of their features.

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Tom
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PostWed Jun 21, 2017 10:11 pm 
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We do know that messages don't go thru.  The question is why.  If in some cases it relates to transmission power then I'm not sure how you can argue it's meaningless.  Of course, you are free to repeat it is meaningless until you are blue in the face, but it doesn't make it so.
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Tom
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PostWed Jun 21, 2017 10:19 pm 
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And no, I don't own, nor have I used either unit.  In the comparison I linked above I do note the author states this:

Quote:
More reliable messaging:
  • 4x higher transmission power, 1.6 watts vs 0.4 watts for the SPOT. In my experience this gives you a higher percentage of successfully sent messages vs. SPOT. This is especially true in difficult transmission areas like dense tree cover and/or tight canyons
  • Better satellite network (Iridium) equals faster and more reliable message transmission
  • You get confirmation that your tracking points have been sent. Again, especially helpful if you are a difficult transmission area
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dla
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dla
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PostWed Jun 21, 2017 10:32 pm 
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Tom wrote:
4x higher transmission power, 1.6 watts vs 0.4 watts for the SPOT. In my experience this gives you a higher percentage of successfully sent messages vs. SPOT. This is especially true in difficult transmission areas like dense tree cover and/or tight canyons

So one person's anecdotal "evidence ", (which of course is not documented), fits your bias and that becomes your "evidence"?

I'm trying to say politely that the author would have more credibility if he did more than "recollect". I think it has to do with some version of the placebo effect.

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