Bushwalk Australia

Discovered on the weekend my ETREX H is useless under a canopy.......surprised? not really although it did struggle even when the canopy did open up a bit.

Just wondering if newer GPS's perform better when tree cover increases or the canopy opens up a bit. I see some GPS's have an external antenna.

Based on video of say the OLT I doubt my old H would log all the way.

Q. For those logging the OLT, which GPS do you use and did its in maintain satellites in the heavy forest areas??

With older eTrex units, it's not just an issue of antenna performance but also the processing chip. Current generation GPS processing chip are much more efficient and can achieve a location lock at a fraction of the time taken for older chips. Further, current units take signals from both GPS and GLONASS satellite constellations. Obviously there'll still be physical limitations with the current generation of GPS units but they are much more usable. Yes, water (rain/snow) and canopy will still degrade the signal but that's just the nature of radio transmission. Fact is, unless you are doing a professional survey, just use what you have and edit your log file. They are all consumer units.

Thanks GPS.....

I think what I have is at the bottom end........some times it took 10 min to lock on to satellites when there was a decent opening in the canopy.

If anybody know echo point campsite, I could not get a location.

I think I might upgrade as I do not have a serial cable for the old H.

As GPSGuided posted, it's not all about the antenna type. The newer chips also see more satellites than the older chips did. Using Glonass Satellite constellation, it can access a further 24 satellites to determine position in addition to the GPS constellation.

I've been doing some testing of my Android phones recently, and an older Sony Xperia phone bought around 2013 which uses a GPS only chip sees only around 13 satellites at a time, and locks on to 5/6 to get a fix. In the same conditions (side by side), the newer Broadcom chip in my newer device sees on average 30 satellites, and uses 13-15 to get a fix.

I've mentioned the antenna types in another post earlier viewtopic.php?f=21&t=20044#p267568. My Oregon 600 and eTrex 30 both have the internal ceramic patch antenna, and have a quicker fix than my older Garmin 60 which had a protruding antenna. The Oregon seems to be better than the eTrex 30, but my testing wasn't scientific, just based on how quickly it locked on. I've used both in mixed tree cover, and they've worked fine with no dropouts. I've not used them in thick rainforest canopies yet.

weeds wrote:I think I might upgrade as I do not have a serial cable for the old H.

Wise. They are electronic gadgets and get superseded in time. It's just not worth struggling with those older devices beyond 2-3 generations.

weeds wrote:Discovered on the weekend my ETREX H is useless under a canopy...

I use my Etrex H and my Etrex 20 at the same time. The 20 goes into the pack top pocket while I use the 'H' in the hand. They log the same and are as accurate as each other in all terrain and close cover! I made sure my 'H' was updated to the it's last firmware update which is v3.80. None of the problems as you have suggested.

PS: I have a third 'H' whose firmware is v3.30 and it will loose 1 km in a day hike, so your issue could be the firmware version.

DIY Garmin Etrex H PC interface data cable
The 3 pins you will need for the GPS are pin 2,3 and 5.
Please note that colours vary from cable to cable and are NOT standardised!

PIN Name Direction Description
1 CD «— Carrier DetectPin
2 RXD «— Receive Data
3 TXD —» Transmit Data
4 DTR —» Data Terminal Ready
5 GND System Ground
6 DSR «— Data Set Ready
7 RTS —» Request to Send
8 CTS «— Clear to Send
9 RI «— Ring Indicator

Advanced user manual (500kB PDF) supplied by Garmin. Available only in electronic version. With the eTrex shipped only beginner's manual.
http://etrex.webz.cz/doc/advancedmanual.zip

Garmin interface (170kB PDF) documentation. Specifications of a communication protocol between Garmin GPSs and computer.
http://etrex.webz.cz/doc/intefacespec.zip

Service mode

eTrex has some features which could be showed by invoking service menu. This hidden screen is used for testing and service purposes by Garmin, therefore is undocumented.

Service mode is displayed when keys "page" and "up" are pushed where powering up the unit.

As a main feature must be noticed internal thermometer (accuracy 1°C). It shows internal temperature of eTrex. It's used for compensation of temperature drift of clock crystal, because the very precious time is needed to know, when tracking GPS satellites. So note, that value displayed is not outer temperature. But it's near to it and good enough for outdoor usage.

Other interesting values appear in service menu. Information about current status, firmware versions, system's integrity check, current time and many more.... Pressing "page button" you can pass through complete display check and functions of all buttons could be tested using icons in bottom part of screen.

Pressing "up"+"enter"+"on/off" keys in service mode will reset the eTrex to factory defaults. So, all pre-sets and data will be lost.

----------------------------------------------------------

A home-made Garmin eTrex data cable

http://www.jens-seiler.de/etrex/datacable.html

weeds wrote:Discovered on the weekend my ETREX H is useless under a canopy.......surprised? not really although it did struggle even when the canopy did open up a bit.

Just wondering if newer GPS's perform better when tree cover increases or the canopy opens up a bit. I see some GPS's have an external antenna.

Based on video of say the OLT I doubt my old H would log all the way.

Q. For those logging the OLT, which GPS do you use and did its in maintain satellites in the heavy forest areas??

Weeds as you know I logged my OLT walk recently so I can offer my findings with my GPS. Which incidentally is a Garmin 60Cx.
I didn't buy my gps for bushwalking, I bought it for motorbikes so I don't know if its a popular model for bushwalking, however it doesn't weigh a lot. I use 'shonky' maps on mine.

Anyway, I used to own a GPS60 when they first came out and it was a great unit but it did tend to drop out in thicker bush. I managed to smash it to pieces in one of my bike crashes. But because I had invested quite a bit in handlebar mounts etc I replaced it with another 60 series but the newer one at the time that had a better chipset and it 'never' drops out in thick bush usually.





However ironically it did drop out on the OLT right near Echo Point. It was really odd, I have owned it for several years now and it has never dropped out anywhere, even when walking indoors briefly. But for what ever reason as I was near or leaving echo Point area it lost its satellite connection and it took a good 20 minutes to find it again. It was a definite one off though.

But when it comes to modern GPS's, which mine isn't, its now a few years old, I have no idea whats the best to use. Keithy and the others are far more up with it than me. Being a bit of a tight a#$e though, if I ever lost mine I would buy another one the same. Mainly because you can buy them cheap second hand on eBay. Perhaps Id get the next version up that has the barometer and it can log your total elevation changes for an entire walk without having to use 3rd party software.

I hope that helps.

I'm betting my H has never had its software updated.......might try and make a cable.....

Thanks for the replies guys.

I used my Etrex30 some months back when struggling through a gully of rainforest for an hour or so. It didn't drop out.

This is my experience with an older Magellan 400 and a much newer ETrex20. Both used in New Zealand under heavy forest cover of beech trees.The Magellan 400 dates from 2007. I was doing a six day trip in Nelson Lakes National Park and the batteries in the Magellan would only last about eight hours maximum so the I GPS was switched off most of the time except when needed to confirm position. found that it would never acquire its position in the forest from power up. The only time it would acquire position from power up was in a clearing with clear view of the sky. Even then it could take a minimum of 10 to 15 minutes to get 2D position. However if it had position and was left running then it would still plot the position quite accurately although any height information would get quite inaccurate (normally 4m tolerance reported but under tree cover this ballooned out to almost 100m tolerance).

Took the ETrex 20 to New Zealand last month. The first time I switched the GPS on in New Zealand was in Arthur's Pass National Park in middle of beech forest. I guess that the data in the device was what was held over from its last use in Australia which was some months prior to this New Zealand trip. It never acquired a single satellite. However when I emerged from the beech forest onto the river flat with clear view of sky, it quickly found the satellites and established its position. Thereafter in the whole three weeks I was in New Zealand the GPS never had any further problem logging position from power up under forest canopy..

Canberra Trekker wrote:Took the ETrex 20 to New Zealand last month. The first time I switched the GPS on in New Zealand was in Arthur's Pass National Park in middle of beech forest. I guess that the data in the device was what was held over from its last use in Australia which was some months prior to this New Zealand trip. It never acquired a single satellite. ...

This is true of most newer GPS units. The initial boot is the "Cold Start". To get a successful cold start, the GPS has to have a current almanac, a reasonable expectation of its current location, and a reasonable idea of the current time. I've found the cold starts to take longer when you have moved to a new location/different timezone like when you step off the plane in another country. The GPS has kept the ephemeris data from the previous time it was turned on, and because the time and locations are now incorrect, the satellites it was using for the last fix is probably now not visible, so it has to download the almanac and ephemeris data again.

The older units used to have to search for up to an hour to locate satellites and download the almanac and ephemeris data, but newer ones do this quicker, and you can help speed it up by setting your approximate location on the GPS (which you can on newer Garmin units). Cold starts can take up to 30 minutes from my experience, but from my use overseas it averages 5-10 minutes.

The next step is the "Warm Start". Most Garmin handhelds will do warm starts (using the ephemeris data saved from the first cold start) when possible, so it's like making a predictive positioning based on the previous settings and the internal clock. But once you cross timezones and different countries or moved several hundred kms away from the last GPS fix, I have found it does take longer to get a fix. So usually if walking overseas, I will endeavour to get a fix soon after arriving in the city I'm walking in, so that way the next bootup will be a "warm start" and be quicker, even under canopy. Warm starts can still take up to 2 minutes to get a fix. Usually the warm start is quicker if you are not moving.

The next boot is the "Hot Start", when the GPS hasn't been turned off for too long. Then the fix is almost instantaneous.

GPSinformation has a nice clear article on this, http://www.gpsinformation.org/dale/gpsfix.htm, although is a bit dated now.

One question I've never received a clear answer is, how much additional improvements has the inclusion of the GLONASS constellation made in current generation GPS devices. Whilst I understand the theoretical potentials and the potential avoidance of US military alterations to their GPS network, I haven't seen an obvious change in the performance amongst consumer units. Guess this question also relates to the algorithm used by the signal processing chip, whether they process the two constellations independently or whether the geoloc is calculated using all the available satellites combined? What I have read is that the use of GLONASS increases the battery consumption, but even that's a bit in the air.

GPSGuided wrote: the potential avoidance of US military alterations to their GPS network

And you trust the Russian-operated GLONASS network MORE in this regard?????

madmacca wrote:And you trust the Russian-operated GLONASS network MORE in this regard?????

Not at all and quite irrelevant. The more important issue is to have an alternate system. In any case and AFAIK, US alterations to the GPS system is only subject to their operational needs eg. During the Iraq war. So having an alternate constellation during those times and locations will be beneficial. In due course, it'll be interesting to see whether consumer devices will also support the Galileo and the Beidou constellations, thereby defeating any particular country's attempt to alter this important navigation service.

GPSGuided wrote:One question I've never received a clear answer is, how much additional improvements has the inclusion of the GLONASS constellation made in current generation GPS devices. Whilst I understand the theoretical potentials and the potential avoidance of US military alterations to their GPS network, I haven't seen an obvious change in the performance amongst consumer units. Guess this question also relates to the algorithm used by the signal processing chip, whether they process the two constellations independently or whether the geoloc is calculated using all the available satellites combined? What I have read is that the use of GLONASS increases the battery consumption, but even that's a bit in the air.

When I first got my eTrex 30 I did some testing with it using GPS+Glonass vs GPS alone. There is no setting for using Glonass alone on the Garmin handhelds I have.

My testing was rather unscientific, but involved forcing a reset on the device, then making sure it the reset was recognised through the hidden diagnostic screen, then rebooted, turned on and timed. This was to make sure it was a Cold Start for both scenarios. On older units there was a way to force Cold Starts through a service menu, but I couldn't find one of the eTrex 30.

In Melbourne suburbs in a playing field with open sky, the GPS+Glonass setup was marginally quicker in acquiring a fix, but only marginally. I did the same test in the CBD, near the corner of Russell Street and Collins Street, and it was a bit quicker again. I can't find my data anywhere anymore, but it was around 5 minutes difference or less in the CBD with urban canyons, but in the burbs, it was around 1-2 minutes difference.

Not sure on the extra power consumption for using Glonass on my eTrex 30, but or my Oregon 600, someone worked out that turning Glonass on used an additional 15mA.

Interestingly, when I was in Europe last year, in some Scandanavian and in the Baltic countries, I noticed that I had no access to Glonass satellites (it shows up as a different set of satellites on the Oregon 600 satellite page). I wondered if this was intentional, but when I went through Kiev, I noticed that Glonass satellites were visible again.

So now I usually have the setting set to use GPS+Glonass for a Cold Start, but after that, I switch it over to GPS only.

Thanks for that experience and insight. I've been thinking about switching off the GLONASS service too on account of power saving. But things haven't gone critical yet. Worth keeping it in the back of my mind.

keithy wrote:In Melbourne suburbs in a playing field with open sky, the GPS+Glonass setup was marginally quicker in acquiring a fix, but only marginally. I did the same test in the CBD, near the corner of Russell Street and Collins Street, and it was a bit quicker again. I can't find my data anywhere anymore, but it was around 5 minutes difference or less in the CBD with urban canyons, but in the burbs, it was around 1-2 minutes difference.

That makes some sense. I would be expecting little consistent difference when you have a full view of the sky. But when part of the sky is obscured (either buildings or terrain), then the odds of being able to acquire the minimum 4 satellite signals in the part of the sky you can see is higher with 2 different constellations of satellites, than just 1.

GPSGuided wrote:

madmacca wrote:And you trust the Russian-operated GLONASS network MORE in this regard?????

Not at all and quite irrelevant. The more important issue is to have an alternate system. In any case and AFAIK, US alterations to the GPS system is only subject to their operational needs eg. During the Iraq war. So having an alternate constellation during those times and locations will be beneficial. In due course, it'll be interesting to see whether consumer devices will also support the Galileo and the Beidou constellations, thereby defeating any particular country's attempt to alter this important navigation service.

Since your post, I have done a bit of internet digging on the issue of degrading the GPS signal. Bill Clinton declared in 2000 that the US would no longer do this, and the latest satellites do not include the Selective Availability feature. http://en.wikipedia.org/wiki/Galileo_%28satellite_navigation%29#Political_implications_of_Galileo_project

With competing satellite location systems now launched/launching, it seems jamming the enemy's signal is now the preferred method of meeting operational needs, rather than degrading your own.

madmacca wrote:With competing satellite location systems now launched/launching, it seems jamming the enemy's signal is now the preferred method of meeting operational needs, rather than degrading your own.

Thanks for the link. I have heard of similar but there's always the option of a back flip or the system going down for innocent reasons. A backup alternative is never a bad thing. As for jamming and disabling enemy's satellites, let's hope the world would never get to that point.

GLONASS! more like GLASNOS...

... It is an adjunct to the US system only as the Rusky depend of GPS just as much as we do, GLASNOS just covers Russian blind spots.

Basically for us it means more birds in the sky so more chance of getting a better triangulation pattern in heavy terrain than with just GPS.

The only one that actually affects accuracy is WAAS as they only appear on the horizon for us and may push out accuracy.

However WAAS is great when local differentials transmitters are used to support local areas such as fishing, diving and airports, etc...





edit: corrections made to my bad spelling

GPSGuided wrote:

madmacca wrote:With competing satellite location systems now launched/launching, it seems jamming the enemy's signal is now the preferred method of meeting operational needs, rather than degrading your own.

Thanks for the link. I have heard of similar but there's always the option of a back flip or the system going down for innocent reasons. A backup alternative is never a bad thing. As for jamming and disabling enemy's satellites, let's hope the world would never get to that point.

Let's hope it never comes to that indeed!

Although I would much prefer jamming (which can be turned off with the flick of a switch), than the shooting down of satellites, which leaves space junk in orbit for years.

Zone-5 wrote:However WAAS is great when local differentials transmitters are used to support local areas such as fishing, diving and airports, etc...

Had the opportunity to use WAAS in the US back in the mid-00s but have not bothered to activate it since. Meaningless for our part of the world AFAIK.

Otherwise, I'm looking forward to seeing the Galileo system up and running for its improved resolution. Guess that'll be the time to upgrade my Oregon 650, not before. Thinking again, maybe by then, my iPhone 8S will fully cover all my GPS needs.

By then there will be a GPS in my toaster...

GPSGuided wrote:

Zone-5 wrote:However WAAS is great when local differentials transmitters are used to support local areas such as fishing, diving and airports, etc...

Had the opportunity to use WAAS in the US back in the mid-00s but have not bothered to activate it since. Meaningless for our part of the world AFAIK.

Yes, WAAS and EGNOS does not exist in Australia, so turning that function on if your GPS supports it does not do anything. I used EGNOS on when I was in Europe last year, but didn't note times to GPS reception or improved accuracy (I probably should have, as EGNOS under optimum situations can improve the accuracy down to around 1.5m).

I had originally thought that turning it on would drain more power, but some folks who hooked up a multimeter to a running Oregon reported that turning WAAS/EGNOS on did not draw additional power.

But out of habit I still turn off WAAS/EGNOS when in Aust/NZ, but turn it on in Europe/US.

My Etrex H will pick up WAAS in Adelaide but it's right on the horizon and not always there. Yes it's there but it does nothing for improved accuracy!

Zone-5 wrote:My Etrex H will pick up WAAS in Adelaide but it's right on the horizon and not always there.

That's interesting. When you got a fix on the WAAS, what did the satellite picture say? Do you know which satellite it was showing? Usually the Garmins will report satellite numbers greater than 32 for WAAS satellites (when you have Glonass off - if Glonass is on, some satellites greater than 32 are Glonass sats). I know that 35, 47, 48 & 51 are US WAAS, and 33 (although some people on the east coast of the US/Canada see this one as well), 37, 39 are European EGNOS . Then when you have a WAAS lock, older Garmins use to show a "D" in the satellite bar showing those GPS information has been corrected with the Differential WAAS data.



This is the WAAS reach. The satellites are geostationary so stay in a fixed position over the earth.

From http://www.nstb.tc.faa.gov/images/GeoFootPrint.gif

One of the WAAS birds might be visible from NZ, but I can't remember seeing them on my Garmins when I was across the ditch, but also can't remember if I had WAAS enabled when over there. But for WAAS to work, there needs to also be a ground reference station. And as there are none in AU/NZ, even if the GPS can receive WAAS, the signal has not been corrected and will not improve accuracy. For what it's worth, I've not been able to pick up any WAAS birds from Melbourne on my eTrex 30 or Oregon 600.

And if you are interested you can get get the real-time display of the full WAAS correction area includng ionospheric correction at this page
http://www.nstb.tc.faa.gov/RT_VerticalP ... nLevel.htm

I can only go by the satellite numbers on the screen of the Etrex 'H' and the 'D' that appears in the signal strength bars.

The two numbers that also appear on the sky view screen when WAAS is enabled coincide with those satellites allocated to the WAAS implementation.

It only happens rarely but it has happened!

Zone-5 wrote:I can only go by the satellite numbers on the screen of the Etrex 'H' and the 'D' that appears in the signal strength bars.

The two numbers that also appear on the sky view screen when WAAS is enabled coincide with those satellites allocated to the WAAS implementation.

That's really interesting. I am curious if it happens again if you can note the Satellite ID number that shows up on your Etrex H. There was some talk about the Japanese SBAS being tested in our region on the pilot forums sometime back, but I don't know if they show up on Garmins with WAAS/EGNOS enabled. Maybe the Japanese SBAS being trialled is showing up as WAAS/EGNOS satellites on Garmins. The "D" should only show up when the WAAS differential data has been received by the GPS and corrected with the signal from ground reference stations.

This map is similar to the earlier one I linked, but also has the extend of the signal from the ground reference stations (shown in light grey overlay). This is the distance of around 200 nm from the nearest ground ref station.


Older Garmin units like the H allowed for 19 WAAS/EGNOS/MSAS satellites as specified in the FAA TSO C-146 http://www.airweb.faa.gov/Regulatory_an ... /C146a.pdf

If you see WAAS satellites on the screen it shouldn't move like the other GPS low earth orbit satellites. Satellite ID numbers on the Garmin use a sligtly modified unique NMEA IDs to identify the sats being tracked.

PRN Sat Type
01-32 GPS
33-63 GPS
64-96 GBAS
97-119 GBAS
120-158 SBAS
159-210 Future GNSS

Garmin Sat ID
01-32 GPS
33-63 SBAS (which is derived from the actual SBAS designation - 87)
65-88 Glonass (which is derived from the Glosnass slot number + 64)

The one closest to the east coast of Aus and NZ is the Intersat's Galaxy 15 which has a geostationary orbit on longitude of 133W. It fell out of orbit a few years ago when they lost control of the satellite, but they managed to recover it and it is back in it's original orbit.

So the Intersat Galaxy 15 133W satellite which has a PRN identifier of 135, should show up as satellite ID 48 on the Garmin.

So if you notice yours picking up WAAS again, it would be cool to note which satellite it is.

EDIT: I forgot about the Indian SBAS network GAGAN. They have a couple of satellites up there now, with another launch later this year. Their grid was to extend down to cover parts of south east asia as well, but I'll have to look up what their satellites PRNs are and their orbit longitudes. It's possible the Indian satellites can be seen from Australia.

EDIT 2; Reading up about the Gagan system, the two Indian GAGAN sats up now, positioned at the equator; the GSAT-8 (PRN 128 NMEA41 55°E) and GSAT-10 (PRN 127 NMEA 40 82°E). They have a combined coverage from Africa to Australia, and the system can support 45 ground stations, with room for 30 new stations in neighbouring countries within the GAGAN satellite footprint. There is another launch intended for December this year of the GSAT-15. However, without a ground reference station in Australia, the signal is still useless (similarly people in South America can see the WAAS satellites, but as there are no ground reference stations there, the GPS signal isn't corrected so the accuracy isn't improved).

So if your eTrex H picks up satellite 40 or 41, that's the Indian GAGAN system.

Been using mt Etrex 20 and Etrex 'H' side by side for all my recent hikes. Not a great deal of difference in accuracy besides one has map capability and the other does not. The main thing I measure is speed averages, stop times and trip odometer. On GPS compass and maps are very rarely used if ever!