doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Global Positioning System

Lee, there is no charge for using GPS--it's in the public domain. Yes, map updates will cost a small amount.

good thing.

better not let the new batch of politicians hear about that. they will add hefty taxes/fees in the name of saving the environment. Probably find some way to add them to the propoesed Obama Cow Flatulance tax in the name of Global Warming.

Lee, Was that really necessary?

GPS was pretty much paid for in the 1980s out of the DoD's budget to the tune of 10 to 15 billion $US. The birds with those atomic clocks were launched just after the 1983 realization/model of the earth was calculated, viz. NAD(North American Datum)1983. And much new data was collected quickly for yet another realization, WSR84. Any rate, color just burns power and check for the Waas capablitity(give ellipses of error near 10 meters) which is land based correction from each coast on the North American continent. Works great when they are broadcasting accurate corrections. Have a look at the Rino com. devices also. I think Cabela's has them.

Kind Regards,

Raimey
rse

Italian SxS. I differ with the recommendations above regarding the Etrex by Garmin. It has a pretty minimal internal antenna and as I proved repeatedly this past summer even a single decidious tree will block it from receiving enough signal to operate. (I was on top of the highest ridge line in Pennsylvania but under trees this summer and the unit could not acquire enough signal to operate but my car mounted GPS functioned perfectly.) Oh yea, I didn't buy this one, a guy who got lost depending on it on the Kaibab gave it to me to use as a demonstrator in Hunter Education Class. In the desert where you have a totally unobstructed sky the Etrex is good enough if all you want is a set of way points to get you back. But get in any deeper and you will have to go hunt for open sky to get good readings. You get what you pay for and Garmin's upscale units like the Oregon 400T does just about everything and is much more user friendly. Of course it costs more too. Go to Sportsmans Warehouse or Cabelas or Bass Pro shop and have them demonstrated for you.

That's a good point on canopy(limbs only are canopy): it will not penetrate it. And when you do get data, it is corrupted by multipath. As far as antennas, if you don't have a external choke ring, you are not going to know the ground truth/correction postion with which to compare anyway. If you are within 10 meters you are doing excellent. Always hold the device as high as possible before saving a set of coordinates to get the best possible horizon.

Kind Regards,

Raimey
rse

I had an eTrex, and just sold it on ebay for about $90, and bought the Garmin 6oCx. I had two issues with the eTrex - the overhead canopy which has already been discussed, and the lack of memory to download large maps. The 60Cx solves both those problems. It's bigger, but far more capable

I'm no apologist for any company and am aware of canopy in acquiring signals. In my province canopy is not a problem during hunting season and rarely during fishing. Going in, taking a shot at lake- or road-side provides lots of sky. Just punch that waypoint when you're coming out. Fifty-foot or less accuracy from my inexpensive etrex Venture has been backing up my dead-reckoning for the last five years. Its repeatability to a waypoint has been as close as three to five metres.

Fifteen years ago, my son, chief pilot for McCain's, bought a $1,500 Garmin for the hell of it and attached an antenna with suction cup to a Falcon 50's side-window. The expensive inertial navigation systems were all over the place during oceanic travel. Approaching, Europe he asked Shannon for a report on the Garmin's positioning through the "gate." Dead-centre.

The basic Etrex is not map capable. It is a basic GPS. The canopy problem is horse hockey. I have had them since they came out, 3 iterations, and have never had a major problem. The newest one acuires satellites in seconds. I think some of the negative comments are being made from reading material, not practical use. I just bought and installed in my wifes car, a Garmin NUVI, now theres a system for the directionally handicapped..

It's according to what you are using it for. Regarding canopy and terrain, I can show you strings of noisy data that have multipath issues, but then again I use similar single frequencey units at about 5 times the cost with sub-cm capability which the average person hasn't any use for. Single frequency units are heavily affect by canopy and terrain. There's not another frequency for a check. When the data leaves the bird it has a time stamp. And when you catch it with your device, which is just a data logger, you know the time. Using both known time stamps and the speed of light, the distance from the birds to you can be calculated and a position also calcualted thru least squares adjustment with knowns and unknows equations. So a deflected/retarded signal from one bird, say on a 10 second data capture epoch, will put you at a seemingly longer distance and your position cannot be resolved.

By the way a second was added to the time to better model the Earth yesterday, which made it the longest day, which you wouldn't notice on a handheld 10m error of ellipse unit. If you haven't any accurate position to compare your position or check your device, you'll never know the difference.

Kind Regards,

Raimey
rse