The case design will be completed in about a week for the first batch of ST900e's.  Lock times are fantastic and the new onmi directional antenna allows for more ways to hold, mount or position the unit and still get very good GPS coverage.

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If you are looking to extend your range may I suggest taking a look at products from www.l-com.com. To extend your range look at:

1. HGV-906U : a two foot Omni directional antenna. They have bigger ones if needed.

2. CA4N025(25Feet) or CA4050(50 feet): LMR-400 low loss cable.  Only use the desired length  i.e. don't order 50 feet if you only need 25 feet.  Keep it under 100 feet for best results.

3. CA4NMRSF002 adapter cable - N Male to RPSMA (attaches the LMR-400 cable to the base station receiver connector).

4. AL-NMNFB-9 lighting arrestor...always a good idea. Connect this the the CA4NMRSF002 to make is easy to get to if needed.

We have customers using different antennas for different jobs.  If maximum distance is required us directional antennas like a Yagi or panel antennas.  In fact, one of our customers, Charlie Wittman, uses both a panel antenna for maximum vertical reception then flips a switch to the Omni antenna for maximum down range reception.

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ST900e ....ironing our a issue with the antenna and GPS chipset.

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Antenna Tricks

As many of you know, optimizing RF systems for really long range can be tough.  There are many factors that impact the range of an RF system including output power, reciever sensitivity, and antenna type and placement.  Many people under-estimate the value of the last one, but it has the biggest impact.  Two pointers to consider when maximizing range:

Fresnel Zone - the concept here is that between two antennas for a given RF wavelenght is a football shaped 'zone' that must be free of obstructions to maximize range.  At 900 Mhz, this zone is as fat as 95 FEET in the middle if you are tracking at a range of 10 miles.  At 1 mile, it is 32 feet.  Put another way, if you have a transmitter and a base station being held in hand on flat plane, you will interrupt the fresnel zone with a transmission of only a few hundred feet.  This degrades signal dramatically.  At 2,000ft it is unlikely the data will make it.

HOWEVER, if you put the antenna up 95ft off the ground on both ends, 10 miles will be possible with no interference.  OR, if you are tracking something in the sky, your fresnel may be clear because you are pointing UP.

Radiation Pattern - Your simple dipole antenna has a 'radiation pattern' that is not really omnidirectional as is often discussed.  It is 'pretty much' omni directional, but only perpendicular to the antenna.  In other words transmitters 90 degrees to the side will have maximum range, and transmitters the antenna is 'pointing at' will have the worst range by far.  This is the OPPOSITE of directional antennas that are designed to be pointed at the transmitter. (Courtesy of Maxstream/Digi's web site)

What this illustration shows us is that for our OMNI antenna, your range at the tip of the antenna will be terrible - even worse with high gain omnis. Range may be perhaps less than 2,000 feet or so even with a clear fresnel zone, but if you rotate that antenna to the side, you will be back in business.  Typically for tracking terrestrial items, omni antennas are mounted up/down to maximize their range.  Further, notice the higher the gain of the omni, the FLATTER the dougnut'.  Actually a 2db gain antenna might perform better at harsh angles compared to higher gain.

If you are tracking flying objects, you should consider mounting your antenna HORIZONTALLY.  This will provide a longer range UP, but not as good along the horizon. 

We know this is true from tracking balloons.  At 20 miles downrange and 50k feet up, we get signal on a 2db antenna with only a 100mw transmitter just fine as long as it is not pointed at the balloon. 

As with everything RF - test to see what works best in your particular situation!

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With the recent heat wave, we've heard some stories from folks using the XT and ST transmitters out in the desert where it gets over 110F/43C.  They report that the units stop working until cooled down.

Fact is that at 43C they are inside their operating envelope and will keep working. The issue is that if you have a unit inside a car or other enclosure out in temperatures of 100+, INSIDE the enclosure can get much hotter.

The units are rated to a max operating temperature of 85C, this is 185F.  Over this range the units are outside of recommended operating temperature and may fail.  The temperature sensor of the ST900e is 125F/257C, but that is JUST FOR THE PROBE END, not for the whole device.

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The XT900 units are literally FLYING off the shelf!  These units perform really well, and with the simplicity of SD card programming, no cables or even software is required to set the parameters.  Users create SD cards with specific 'profiles' such as TracID, update rate, etc.  Then they put these SD cards in a book. Want to check out unit 005?  Just insert the SD card into any XT900 and turn it on.  It is now 'Unit 005'.  Turn it off, take out the SD card, and away you go, or leave it in and record data on the card, as well as transmit it.

The XT900 rechargable battery and integrated case is also a big draw.  Just plug it in to charge it up, and you are ready to go.

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Good things take longer..

Well it is taking longer than we wanted, but the result will be an excellent transmitter unit!  The ST900e represents the ultimate tracker.  With 3D Position indication, G forces, Barometric altitude, super accurate temperature, and an excellent GPS with omnidirectional antenna!  The radio options are amazing also - allowing any of 3 different types of radios to be used from Zigbee to 1 watt native support (no adpater board).

Did I mention it also records, and has some new modes that are really interesting?

• Bump mode - uses the accelerometer to detect movement, and only sends a position updat if the unit is moving.
• Static threshold - set the GPS to only report new position data if moving - avoids 'wandering' while sitting still
• Short sentence - allows the unit to send short position only sentences to increase speed or density of the network

So, it is a really cool sensor.

Problem is that it is also REALLY COMPLEX.  Our ace firmware designer is hard at work with only a few final items to wrap up before our final spin, then we'll be ready.  Our current challenge is the SCP1000 sensor. The folks from VTI are being very helpful with this, and when done, you will be able to see very minute changes in altitude very accurately.

As you can see above, the SCP1000 is SUPER SENSITIVE!  Able to show the difference of just a foot in real time.  This is a much better way to determine altitude than using a GPS for short term altitude readings because GPS vertical accuracy is considered very good if it provides 25ft of accuracy, and most are plus or minus 100 feet vertically or more.

So, probably a 3 week slip here, sorry folks, but you want us to put in the extra hours for a quality product!

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The new web site is coming along!  We are using Joomla to better handle file downloads, and content management.  As we go through the transition, please let us know if you find broken links, or things that are just not quite right and we'll fix it for you.

Also, if there is content you'd like to see, please let us know!

Thanks,

GPSFlight Web Team

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We just figured out how to send data at 30ms time slices.. Before the minimum was 90ms. This may create the ability to update 3x more units per timeslice..

 

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We did an interesting experiment with the XT900 last week. We turned it on (in record mode only) on a plane from SFO to SEA.  The unit locked fine even tho inside the plane (near the window) and recorded the whole flight in 1 second increments.  Very interesting experiment.  Made a track visible in Google Earth from SFO right to SEA at 35,000 ft.  Pretty cool stuff.

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