allout

Yes, from what I have read both the BT-338 and BT-359 are fine GPS units. I just went through days, in my off time, reading reviews in order to purchase a portable camera. I was hoping for a hands down winner is the GPS units like the x50/51 in the PPCs. There is not one, yet. I am certain that the week after I replace my old dead 360 Pharos, the Axim of GPS units will be released. It will boast a 20Hz refresh, a new lifetime beta battery, and be the size of a stick of gum.

The three major characteristics I find important.
a. Size
b. Battery life
c. 5Hz

The GPS will be use for advanced city driving like Houston, maybe a little aviation, and backwoods activities. I am concerned about the ability to track and compass correctly as slow speeds, say up or down hill in heavy brush. Data logging feature is very nice, as long as it will navigate and log at the same time. The MTK chipset seems to be the way to go. If I had to pick now, I suppose it would be the i-Blue 747 if updating the firmware to 5Hz does not void the warranty or cause any weird power issues. I bet if I had an over the horizon radar to spot GPS devices I would see a unit the size of a standard Axim battery with good solar performance, or close to it. I have read some of the post stating the 5Hz is not important. If there is the ability to read at 5Hhz and not forecast I think it is valuable now and especially in the future with the release of new things. Oh, and for those of us that are not going the way of the HTC xxxx, in my opinion the Canon SD1000 is the Axim of digital cameras.

:rolling:

JakeRich

Interesting post. On the 5hz issue, consider this: at 60 MPH (96 kph) in one second you travel about 88 feet (26 meters). The error in each GPS fix, with WAAS, is about 5M or 16 feet, 95% of the time, with the other 5% being worse than that. That error in the system means that the GPS will report, 95% of the time, that you traveled something between 72 feet and 104 feet in that second (22m and 32m). Overall, at 60 mph that kind of error is pretty much negligible, given that the overall lag in reporting is on the order of 0.5 second, or 44 feet, anyway. Most software damps down that wander under the assumption that if you were 88 fps last second you'll probably be close to 88 fps this second.

At 5hz things get interesting. In 0.2 seconds you only travel about 18 feet, close to the error circle of the fix itself. So although you get more updates, the receiver has to damp down that fix-to-fix wander more severely.

Now, if you slow down to a walking speed, let's say 6 MPH instead of 60, the distance traveled in one second is now 8.8 feet, or only half the error of the fix itself. And if you get updates every 0.2 seconds, the distance traveled is now 1.76 feet, roughly 10 percent of the error inherent in the system.

I know that 5hz is all the buzz these days, I just don't know why. Even in an aircraft, since you mentioned it, it's not that critical to know where I am more frequently than once per second, unless I'm landing, but PDA GPSs aren't certified for that function in any case. If I were using GPS for a weapon that traveled 600 mph, then it would make some sense to have 5hz (or faster) updates to guarantee high accuracy of impact, but given the practicality of the problem i think we're trying to solve as consumers, I don't see the advantage of it. Add to that lack of value that the increased speed of data input adds five time as much demand on the software to calculate and display the results, I can see where 5hz may over-stress (or at least overheat) many PDAs for little additional benefit, if any.

Just my $0.02.

bigtsr

You should look at the ASUS line of pda's before you look to
hard they come with integrated GPS with hook up for external
antennas and WM5 at a really reasonable price.

allout

Hmm, I see your point, or in fact the lack of a single GPS point and the reality of a moving 5m area. Is the 5 meter error 5 meters from a point making the total of the error 10 meters or is the error 2.5 meters in each direction?

Asus makes some great motherboards. I have two PPCs that I need to use with the BT GPS, other wise this might be a good choice.

JakeRich

With WAAS on and receiving a WAAS signal, your gps calculates and sends your PDA a fix location while you are standing still. You have a 95% probability of actually being within 5 meters of that calculated position. Without WAAS, the 95% distance increases to 12 meters. Now days a lot of receivers use what is called Static Navigation, a trick to ignore any speeds below 3mph or any location changes at that slow speed less than 50 feet. That function eliminates the jumping around that used to be a problem at traffic lights and stop signs.

allout

I see, relatively speaking one is standing in a 5 meter circle.
Here is a picture.

Garmin: What is WAAS?

Current WASS is .9m to 7.6m, data pulled from wiki. If WAAS accuracy increases to let say 1 meter average, would a WAAS GPS receiver reflect this improvement or is the WASS accuracy static an the accuracy is dependant on the receiver? Wouldn’t this increased accuracy be useful in various sports and not just for aviation approaches? For example put a $50 WASS GPS on a soccer or basketball player and coaches could view, save and compare. In pro tennis the players have access to data for a match including their body’s velocities (not GPS based).

This is from a manufacturer of GPS systems for sailplane competitions.
“The integral GPS and logger are IGC Approved for all types of soaring accomplishments. The 302A has more memory for flight logs and waypoints than any other logger. It will hold up to 100 hours of flight log positions @ 4 second intervals.” That is this year what about next year.

Amamba

I have a BT-359 and it refuses to work on Ax51v with MS BT stack, I had to install Broadcomm stack to make it work.

Other than that, it's a fine little receiver, very portable and reliable. The battery lasted me some 11 hrs of total work within 3 days before I had to recharge. I found that some software (eg OCN) seems to work better with it switched to NMEA protocol, although this is probably software-related.

BTW, isn't a "once a second" GPS position update frequency driven by homeland security rules, so you aren't going to get a true real-time location while moving, regardless of receiver used ?

DigiNetLink

The battery life in BT-338 will be longer, ther then that both are great and quality receivers. Out of 100% sales we have maybe 1% return and the reason usually - incorrect configuration.

__________________
DigiNetLink.com GPS Online Store Team

allout

One of the GPS suppliers wrote this in reply to my low speed question;
“With MTK chipset, there is no such thing as static navigation filter. SN is an unique function for SiRF chipset only. However, earlier MTK chipset does have issues with low speed tracking but it has been resolved since May 2007. Any MTK chipset GPS that you buy after May 2007 will not have low speed tracking issue.”

I have learned of another chipset type, the “ublox”. It looks like this chipset could have legs. The Wintec WBT-201 has this chipset and is a very nice looking receiver. It is waterproof and Bluetooth data transfer. It looks like the MTK chipset is the best for battery like. The Solar Qstarz Super 99 BT-Q1200 is also a nice looking thin MTK solar device.