Thoughs between Garmin GPS units

[Kurchian]

60CSx vs etrex

I bought an Garmin etrex several years ago. I brought it into the woods with me a few times and couldn't get a signal in deep woods. I stopped using it for hiking in NH.

I got a Garmin 60CSx this year and had been using it for geocaching. I decided to try it in the Whites this season and I am amazed at how easily it locks into satellites. In fact, after climbing Moriah last week I stuffed it in my backpack after I summited. I descended the trail and threw it in the trunk of my car and drove home. When I got home three hours later I found that I had forgotten to turn it off. It had continued to track all the way home with no misses! The 60CSx is expensive but it has an outstanding antenna and you can download maps to it.

 

[darren]

threw it in the trunk of my car and drove home. When I got home three hours later I found that I had forgotten to turn it off. It had continued to track all the way home with no misses!

Wow, I know the quad helix antenna is the way to go, but that is amazing.

I used a Magellan Merridian "color pro whatever" at work and I got it because of the water proofing and the quad helix antenna. That thing is good but I never tried it in a trunk. I was going to get one (after all, I have access to some nice maps) but that whole line is discontinued. From what I've read. the Garmin 60/76 CSx sound even better.

One thing about 60/76 comparisons. I have been reading reviews and one negative on the 76 is that the buttons are above the screen and you have to reach over the screen (blocking your view) to hit the buttons. Not quite user friendly. Looks like I am leaning towards the 60 and a leash. Well, no time soon though. Still a lot of money with the maps.

- darren

 

[DougPaul]

I bought an Garmin etrex several years ago. I brought it into the woods with me a few times and couldn't get a signal in deep woods. I stopped using it for hiking in NH.

I got a Garmin 60CSx this year and had been using it for geocaching. I decided to try it in the Whites this season and I am amazed at how easily it locks into satellites. In fact, after climbing Moriah last week I stuffed it in my backpack after I summited. I descended the trail and threw it in the trunk of my car and drove home. When I got home three hours later I found that I had forgotten to turn it off. It had continued to track all the way home with no misses!

Impressive little beast, isn't it...

I also have an eTrex Vista. The 60CS is an improvment on the Vista and the 60CSx just blows either of them away in degraded signal conditions.

The 60CSx is expensive but it has an outstanding antenna and you can download maps to it.

This is a common myth--both the quad helix and the patch antenna are about the same in performance. (Most external antennas use patch antennas.) The important difference is the GPS chipset--the SiRFstarIII chipset has over 200K correlators which makes it possible to acquire signals very quickly. ( http://www.sirf.com/products/GSC3LPProductInsert.pdf or http://www.sirf.com/products/GSC3LTProductInsert.pdf )

Doug

 

[DougPaul]

Wow, I know the quad helix antenna is the way to go, but that is amazing.

As noted it the previous post, this is a common myth. Both antennas have similar performance. The important difference is the new GPS chipset (SiRFstarIII).

I used a Magellan Merridian "color pro whatever" at work and I got it because of the water proofing and the quad helix antenna. That thing is good but I never tried it in a trunk. I was going to get one (after all, I have access to some nice maps) but that whole line is discontinued. From what I've read. the Garmin 60/76 CSx sound even better.

It appears that Garmin is taking over the high-end consumer market with the 60/76Cx line...

One thing about 60/76 comparisons. I have been reading reviews and one negative on the 76 is that the buttons are above the screen and you have to reach over the screen (blocking your view) to hit the buttons. Not quite user friendly. Looks like I am leaning towards the 60 and a leash. Well, no time soon though. Still a lot of money with the maps.

The corresponding units in each line appear to be electrically identical. There is much debate over which is better and there are devotees of both. It appears that one can easily learn to use either when held in one hand. The 60 line has rubber armor and is a little smaller. The 76 line has a flatter package which might sit on a flat surface (eg a kayak deck) better. The 60 might be better for hiking and the 76 might be better for boating. If you can, go to a store and actually hold them in your hand and imagine them mounted on a deck.

When it comes down to it, either will work well for both purposes. And get a larger microSD card--a 2GB Sandisk card is available for $31. (Get a Sandisk regular speed card--the ultra does not work and there have been reports of problems with some other brands.)

Agreed--not cheap, but you will be much happier next time a fog kills your visibility or you get "confused". And you might even decide that you want a road map, too--it is very useful in the car, particularly if you drive solo in unfamiliar areas... I will certainly use mine on the way up to Bearly Live.

Doug

 

[darren]

The best orientation for the eTrex C line (internal patch antenna) is flat, as on a deck, and the best orientation for the 60/76 line (internal quad helix antenna) is vertical.

Due to the orientation constraints and the fact that when hiking or biking it is easy to just strap the unit to your chest strap (vertical orientation), the quad helix is the way to go. It also holds true when you are standing still holding the unit. I like to hold it up in front of me in a vertical orientation so I can see the screen. If I put in flat on the deck of kayak, it doesn't really matter because I will be on open ocean so sky view is no problem.

I've seen big differences in chest strap mounted gps units under a tree canopy. The one with a quad helix held coverage 100% of the time and the patch one dropped out all the time.

So while antenna gain might not be very different, orientation is an important factor.

- darren

 

[SAR-EMT40]

So while antenna gain might not be very different, orientation is an important factor.

- darren

Maybe Doug can speak to whether the signal from the sat is vertically or horizontally polarized. I am actually not sure. If thats the case then I believe something like a -30Db loss would be expected in the signal depending on the orientation of the antenna. Of course the signal could be circularly polarized.

Doug?

Keith

 

[DougPaul]

Due to the orientation constraints and the fact that when hiking or biking it is easy to just strap the unit to your chest strap (vertical orientation), the quad helix is the way to go. It also holds true when you are standing still holding the unit. I like to hold it up in front of me in a vertical orientation so I can see the screen. If I put in flat on the deck of kayak, it doesn't really matter because I will be on open ocean so sky view is no problem.

I've seen big differences in chest strap mounted gps units under a tree canopy. The one with a quad helix held coverage 100% of the time and the patch one dropped out all the time.

So while antenna gain might not be very different, orientation is an important factor.

Yes, I've looked at the datasheets and know the antenna patterns.

From a practical standpoint the primary difference is mechanical. Both antennas have their maximum directivity along their axes (along the axis of the cylinder for a quad helix and at right angles to the flat surface of a patch antenna) and the best orientation of the GPS unit depends upon how the antenna is mounted in the GPS unit. (For best performance, the axis of the antenna and its main directivity lobe should be straight up. Ideally, one should be able to receive signals from the entire hemisphere above the GPS.)

Unless you were comparing the quad helix with a patch antenna in an otherwise identical pair of GPSes, the comparison is flawed. The performance difference between an eTrex Vista (patch antenna) and a 60CS (quad helix) is far smaller than performance difference between a 60CS (quad helix) and 60CSx (quad helix + better signal processing).

In the process of recording tracks for my bakeoff #2 (comparing the 60CS (quad helix) and the 60CSx (quad helix + better signal procssing), both with identical antennas and orientations, I stopped for a minute or two under a building overhang. The 60CS track wandered, the 60CSx track stayed put.

BTW, one can carry an eTrex Vista flat on top of one's shoulder, so you can carry the Vista in its best orientation when attached to a pack strap. (One's head still gets in the way, however...) I have also carried a Vista attached to the strap at the back of a baseball cap--works pretty well there too. (However, you have to take your hat off or get the guy hehind you to read it. ) One could also carry it on top of one's head with an appropriate hat (eg in the crown pocket of a Tilley).

If I assume that your uses are equally weighted between kayak and hiking, the generally better skyview from a kayak suggests that you might choose a more hiking oriented GPS to get good performance in both environments. And the signal processing in the 60CSx (or any of the Garmin "high sensitivity" units) is sufficiently good that you can use it upside down in either environment and still get a good lock most of the time.

Doug

 

[DougPaul]

Maybe Doug can speak to whether the signal from the sat is vertically or horizontally polarized. I am actually not sure. If thats the case then I believe something like a -30Db loss would be expected in the signal depending on the orientation of the antenna. Of course the signal could be circularly polarized.

Doug?

The signal is right-hand circularly polarized (RHCP). This solves the receiver antenna polarization issue and discriminates against odd numbers of reflections* to reduce the multipath problem.

* Each reflection of a circularly polarized signal reverses the direction of the polarization and an RHCP receiving antenna will greatly attenuate an LHCP signal.

BTW, I think 24db is the nominal attenuation of a cross-polarized linearly-polarized antenna and signal, but the exact number isn't important. (Don't know for certain what the nominal attenuation is for reverse circularly polarized signals and antennas, but my guess is that it is similar.) It is still a significant attenuation.

 

[darren]

Maybe Doug can speak to whether the signal from the sat is vertically or horizontally polarized. I am actually not sure. If thats the case then I believe something like a -30Db loss would be expected in the signal depending on the orientation of the antenna. Of course the signal could be circularly polarized.

Doug?

Keith

Woah, sounds like there is an electrical engineer hiding behind those EMT patches.

As far as I know, GPS is RHCP (Right Hand Circular Polarization). You are correct, on the 30 dB loss from cross pol signal / antenna. The textboooks will tell you that cross pol attenuation is infinity, but in the real world it is about 30 dB. Kudos to you for not believing the hype of the classrooms.

Due to circular polarization, the orientation discussion is about antenna directivity pattern not polarization. Meaning which way should I hold the unit to point the antenna mainbeam up.

Ok, this is getting too much like work...



- darren

 

[darren]

BTW, I think 24db is the nominal attenuation of a cross-polarized linearly-polarized antenna and signal, but the exact number isn't important. (Don't know for certain what the nominal attenuation is for reverse circularly polarized signals and antennas, but my guess is that it is similar.) It is still a significant attenuation.

OK, Doug beat me to the "submit" button. From what I have seen in the real world it is about 30 dB (loss factor of 1/1000). It holds true for all true cross polarizations. But I'm pretty sure V or H to CP is only 3 dB. Hence the use of CP.

- darren

ps: how do I know that by the time I click the submit button Doug will have beat me again...

 

[darren]

Wow, he didn't.

- darren

 

[DougPaul]

Due to circular polarization, the orientation discussion is about antenna directivity pattern not polarization. Meaning which way should I hold the unit to point the antenna mainbeam up.

Yup.

However, the polarization of an antenna can vary with the direction of the incoming signal. I don't know the details of the polarization changes for these antennas and didn't want to invoke this level of complexity. (The data sheets tend not to mention this issue.) Even if the polarization of the antenna becomes linear from some direction, it is only a 3db additional loss (over the pattern loss), so the biggest effect would be reduced rejection of odd-bounce reflected signals. Thus the directivity of the antenna is still the biggest factor.

Ok, this is getting too much like work...

Yup here too...

Somehow I'll bet that many readers have tuned this thread out by now...

Doug

 

[DougPaul]

Wow, he didn't.

Sorry--I was contemplating my last answer...

And yes, linear to circular polarization (and vice-versa) is a 3db loss.

Doug

 

[Paradox]

I need the blue water maps for kayaking and the topo maps for hiking. The bluewater america map is $150 and the America topo map is $117. So $350 for the gps unit and then another $270 for maps. Nuts. Looks like I will stick to map and compass. .

I don't mean to be a wiseacre here, but do you feel you need nautical charts for kayaking? Sure it would be nice, but knowing the water depth in a kayak doesn't seem to be as important as it would be in a sailboat with a fin keel, or a power boat with its expensive and critically necessary propeller. IMHO having a GPS in the kayak could be a real lifesaver at times. As Doug mentioned fog rolling in, or trying to beat a storm back to your origination waypoint (you could check the ETA on the GPS vrs how fast the front is moving toward you.)

What I'm saying here is that the benefits of having the GPS onboard still exist without the expensive nautical chart data.

 

[DougPaul]

I don't mean to be a wiseacre here, but do you feel you need nautical charts for kayaking? Sure it would be nice, but knowing the water depth in a kayak doesn't seem to be as important as it would be in a sailboat with a fin keel, or a power boat with its expensive and critically necessary propeller. IMHO having a GPS in the kayak could be a real lifesaver at times. As Doug mentioned fog rolling in, or trying to beat a storm back to your origination waypoint (you could check the ETA on the GPS vrs how fast the front is moving toward you.)

What I'm saying here is that the benefits of having the GPS onboard still exist without the expensive nautical chart data.

IMO, the situation is a lot like hiking. Both hikers and mariners have gotten along well most of the time with map/chart and compass. (Both have also occasionally gotten lost, too.) A GPS offers improved navigational capibility, particularly in cases where one cannot see far enough to sight on anything with a compass. Remember, the navigator's desk on a kayak is very small and may be awash making it very difficult to look at a chart, paddle, and keep the boat upright at the same time. (Try reading off cordinates from a chart and punching them into a GPS on a heaving wave-washed kayak deck...) Having a chart built into the GPS brings everything together in one unit. Just like in hiking, a quick glance at the GPS can show you where you are in relation to the surround. And by having the chart in the GPS makes it much easier (ie possible in some situations) to place a waypoint and execute a "goto".

While in theory, one can do the same things with a non-mapping GPS as one can do with a mapping GPS, IMO in practice the mapping GPS is far more useful. Both on land and on the water.


BTW, while draft of a kayak is much less than for a fin keel sailboat, depth is still an important issue. Waves tend to bunch up and get higher (or break) in shallow areas. A kayaker might want to detour around these areas if there is a sea running. And if you get knocked over, you might like the rocks to be ~4 or more feet down... In the book that I mentioned on kayaking around the South Island of NZ, the author used a helmet for landing in surf because he regularly got knocked down and would have to wait for the next gap between the waves to roll back up as he passed through the off-shore breaks.

Doug

 

[Papa Bear]

You might also ask if you seriously need that level of accuracy. (10 meters is more than adequate for hiking). Many seem to be obsessed with accuracy for accuracy's sake. (And many of these same people are ignorant enough to believe the EPE (accuracy) numbers, which means that they don't understand GPS accuracy...)

...

Doug

There is an answer. In another part of my life I'm a bench mark (survey marker) hunter. Triangulation stations on mountain tops are particular interesting targets. Their location (originally established by classical triangulation methods) is known to sub-meter accuracy and in some cases to centimeter accuracy.

So we know exactly where they are, we just don't know where we are. Sometimes they are burried from inches to feet below ground. I would hope with 1 meter accurate GPS and a metal detector, I'd have a shot at some of these that have not been seen in sometimes close to 100 years.

 

[Paradox]

While in theory, one can do the same things with a non-mapping GPS as one can do with a mapping GPS, IMO in practice the mapping GPS is far more useful. Both on land and on the water.

I concur.

BTW, while draft of a kayak is much less than for a fin keel sailboat, depth is still an important issue. Waves tend to bunch up and get higher (or break) in shallow areas. A kayaker might want to detour around these areas if there is a sea running. And if you get knocked over, you might like the rocks to be ~4 or more feet down... In the book that I mentioned on kayaking around the South Island of NZ, the author used a helmet for landing in surf because he regularly got knocked down and would have to wait for the next gap between the waves to roll back up as he passed through the off-shore breaks.

I have two questions: 1) Did he lose the satellite reception while submerged upside down? 2) Did he have an external antenna mounted on this helmet?
Again, I concur, but all the above exists and should have been considered whether not the kayaker has a GPS onboard. BTW the Garmin TOPO software one might use for hiking includes nav aids for the Atlantic and Pacific and Graet Lakes/Lake Champlain. I raced sailboats on lakes Erie and Ontario for 25 years and the nav aids in the areas I am familiar with look accurate to the best of my recollections.

 

[DougPaul]

There is an answer. In another part of my life I'm a bench mark (survey marker) hunter. Triangulation stations on mountain tops are particular interesting targets. Their location (originally established by classical triangulation methods) is known to sub-meter accuracy and in some cases to centimeter accuracy.

So we know exactly where they are, we just don't know where we are. Sometimes they are burried from inches to feet below ground. I would hope with 1 meter accurate GPS and a metal detector, I'd have a shot at some of these that have not been seen in sometimes close to 100 years.

OK. So you are too lazy to search a 100 sq meter area to find the marks...

Seriously:
Greater accuracy would increase the chance that you find the marker.
For only $50K or so, you can buy a Real-Time Kinetic (RTK) system that would give you centimeter accuracy.

If you can't afford that, the GPS system will get better, but it will take a while and you may have to buy a new GPSR or two along the way to take advantage of the improvments.

BTW, if you have been reading claims that the EU Gallileo system will be much more accurate than GPS, they are pure advertising. The claims compare the future Gallileo plans with the current GPS system. The GPS system is improving with time and when and if Gallileo ever becomes operational, the systems will likely be similar in accuracy. One advantage will be that the two systems will be compatible so there will be 60 satellites in the combined system rather than the current 30. There have been some problems with the development of the Gallileo system--it is currently unclear if it will ever become operational.

Doug

 

[darren]

I don't mean to be a wiseacre here, but do you feel you need nautical charts for kayaking?

I used the Magellan Meridian with the standard map and the blue water maps. The blue water maps have way more data. The standard map looked like a joke in comparison. Like Doug said, they show the locations of rocks etc which is important when you are picking a place to land in the fog or in heavy seas. Depth is also important when figuring out tidal rips etc. They also show tidal flats and sand bars. All important data. I also fish and skin dive from my kayak so it is all good data for that too. It is just like using the standard map vs a topo map for hiking.

- darren

 

[DougPaul]

I have two questions: 1) Did he lose the satellite reception while submerged upside down? 2) Did he have an external antenna mounted on this helmet?

1) He makes no mention of carrying a GPS. The trip was made in 2000. For practical purposes, GPS signals do not penetrate sea water.

2) He often took his helmet off when out at sea, so it would not have been a practical mounting location. (The wire would also have been a tangling hazard.)

Besides, all he had to do was keep the South Island on his right...

BTW, he did have a chart washed away in heavy seas at a critical moment.

Again, I concur, but all the above exists and should have been considered whether not the kayaker has a GPS onboard. BTW the Garmin TOPO software one might use for hiking includes nav aids for the Atlantic and Pacific and Graet Lakes/Lake Champlain. I raced sailboats on lakes Erie and Ontario for 25 years and the nav aids in the areas I am familiar with look accurate to the best of my recollections.

Yes I have seen the marine nav aids on the Garmin US TOPO maps--the ones in the Boston Harbor area look reasonable, but it has been too long since have looked at a chart.

You do make a good point--the Garmin US TOPO map does show the near-shore marine nav aids and might be useful to a boater. (A quick check of the Garmin web site map viewer shows no nav aids in Boston harbor. ) The US TOPO maps are rather old and one would risk them being out of date. I presume that Garmin would pay more attention to keeping the Blue Chart products updated.

BTW, my sailing was in a 6ft draft fin-keel sailboat from the Boston area to coastal Maine.

Doug