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Military GPS units?


tachoknight

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Hi all-

 

I've been reading about GPS devices, thinking I want to get on as a second opinion to my iPhone 3gs, and the thing that seems to come up over and over is how much better a military-grade GPS is. It always seems to follow that, whereas a commercial GPS will become inaccurate or lose signal completely below a canopy of trees or in a big city, the military ones will still get you to the penny on the forest floor every time.

 

Does anyone have any experience with the military versions to confirm that? I'm not asking for any secrets, if there are any, to be revealed, I'm just generally curious if you really can get pinpoint accuracy, or if it's just a matter of slightly better equipment and a lot better training (I'd like to think that if I were an army ranger, I'd have 10,000 finds in no time. B)).

 

I was also wondering if the military units are really much more different than your standard commercial ones (i.e. same basic equipment but better software).

 

Finally, I guess the last thing I'm curious about is....what's the point of a military version? As geocaching in general has proven, all sorts of people (including someone like me who can't remember which direction the sun sets) can use commercially available equipment to find ammo boxes, tupperware containers, even film canisters and smaller in both rural and urban areas...what additional benefit would a military-grade GPS be?

 

Just curious,

 

Tachoknight

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Watch this,doesnt seem like there are lots of newer military units around. Commercial ones have their limitations in warfare,but are cetainly more compact,do you really want a bigger bulkier unit just to get more accuracy for geocaching?Isnt geocaching supposed to be a game?If I can walk right to the cache every time and find it as if it were in the open in a bright red box,its going to get boring pretty quick.As far as reception goes I rarely have a problem with my unit.

Edited by Forkeye
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How much does a Tomahawk Cruise missile cost? I forget........... BUT, it is the programmable GPS guidance system built into it that lets it fly through a window 350 miles away. Will your commercial Garmin do that? I would think not.

 

In a nutshell, just what would a civilian need (or want to pay for) that accuracy?

 

Such equipment would be nice to have, but just that -- nice. No real need to thread a needle.

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Actually Prime Suspect is wrong. In 1992 Signal Degration was turned off and this hobby started. We all get the same signals. And as far as under cover there are many that do well especially the 60x series.

Selective Availability was shut down on May 1, 2000 (it was briefly turned off during the first Gulf War as well), and geocaching started shortly thereafter. The newer satellites can't even generate a non-SA signal anymore.

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Actually Prime Suspect is wrong. In 1992 Signal Degration was turned off and this hobby started. We all get the same signals. And as far as under cover there are many that do well especially the 60x series.

You need to get your facts straight. President Clinton disabled SA (Selective Availabiility) so commercial GPS receivers will not have an error rate of 300 feet or more.

 

Military GPS receivers can receive a secured signal. In fields where signal degradation may be applied and commercial units will suffer, the military GPS will still be able to acquire an accurate signal from a military encoded broadcast.

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Here is an excerpt from a paper that I wrote on how GPS works. Should answer your question specifically.

 

The satellites are launched by Delta rockets to achieve their initial orbits but they have a small fuel supply for fine-tuning. Solar panels and batteries are used to power the satellites’ transmitters (The solar arrays can be visible from Earth and look like shooting stars called Iridium Flares. (For more information visit http://www.heavens-above.com). The most important parts of the satellites are their atomic clocks, accurate to within 3 nanoseconds (that is 3 billionths of a second or 0.000000003 seconds). Each satellite carries two cesium and two rubidium clocks (These are the atomic clocks. They are based on the fact that it takes a known exact amount of time for an atom of cesium or rubidium to decay.) They receive data signals at 1783.74 MHz for things such as course corrections and almanac updates. They transmit data on two frequencies, 1575.42 MHz (L1) and 1227.60MHZ (L2), at 500 watts of power. Dual frequencies are used in order to minimize atmospheric propagation errors in military and industrial GPS receivers.

 

L1 and L2 are the signals that our GPS receivers use to determine our position, but they are just the carrier waves. Each carrier wave has binary codes modulated into them. C/A (coarse acquisition) and P (precise) binary codes are modulated into both the L1 and L2 carrier waves. L1 contains C/A and P codes, but L2 is normally set to carry only P code. The C/A code is amplified such that it is 3-6 decibels stronger than the P code. It is modulated onto the carrier wave at 1.023 Mega-bits per second, which results in the entire C/A code repeating itself every 299,739 km of carrier wave (1023 chips with each chip length 293m). When selective availability is on the chip length is changed from 293 m (selective availability was removed by the Clinton Administration May 1st, 2000, opening up GPS usage to the public). The P code is a very long binary code that repeats every 38 weeks in its entirety, but each satellite transmits a different weekly section of the code. This reduces the amount of time required to receive the entire code to approximately one week. The P code is modulated onto the carrier wave at 10.23 MHz and repeats itself every 181,273,389,696 km of carrier wave (chip length is 29.3m).

 

Civilian (commercial) GPS receivers only receive the L1 C/A code. The coarse acquisition code is composed of two signals known as the pseudo random binary code and the navigational broadcast message. The pseudo random binary code is modulated onto the C/A code and repeats every millisecond, but the navigational broadcast message overlays many cycles of the pseudo random binary code. The pseudo random binary code is 1023 chips and repeats every millisecond. There are 32 different pseudo random codes and each one identifies a different satellite. The navigation data is modulated on top of the signature at 50 Hz (by using the pseudo random binary code as a carrier). The navigation message is split up into 25 frames and each frame is split up into 5 sub-frames. A frame is transmitted in 30 seconds at the top and middle of every minute (as measured by the atomic clocks in the satellites). Sub-frame 1 contains GPS week number, satellite accuracy and health, and clock corrections (this takes 6 seconds). Sub-frames 2 and 3 contain ephemeris data (6 seconds each). Sub-frame 4 contains almanac data for satellites 25-32, special messages, satellite configuration flags, and ionospheric and UTC data (6 seconds). Sub-frame 5 contains almanac data for satellites 1-24 and almanac reference time and week number (6 seconds). Sub-frames 4 and 5 are different in all 25 frames. In order to get complete almanac data it takes approximately 12.5 minutes to download all of the data to our receivers (all 25 frames). In order to reduce the time it takes to get a fix with a receiver the ephemeris and clock data is repeated every 30 seconds. This allows us to get a fix quickly (sometimes as fast as 45 seconds), but without receiving all of the almanac data.

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Holy cow, VIctory Mike!! I've been using military grade GPSr's for 19 years and never had a more technical explanation B)

Accurate as heck, however.

 

To give the perspective of someone who has used both military and commercial.......

 

the ones i use at work (i am in the Navy) are accurate to 1 meter. my Oregon & Delorme, standing in the same spot at the same time are off by 10 meters (give or take a few feet). most military models don't have the viewscreen, so i had to do some math to figure my actual location (at the end of a pier in Norfolk, VA). the military model was the most accurate. it was also the hardest to use.

 

as for the question of signal lock, the electronics don't know if they are in a military GPS unit or not. the signal is the signal.

 

personally i use a commercial raytheon gps/radar/depthsounder at work. i operate harbor security craft used for protection of ships. the mil grade units are time intensive and require specific training on their use. the commercial units may lack the super-accuracy, but when the difference is only 50 ft or so and you are on the water, it doesn't matter that much.

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The military grade would only help if anothyer one was used to hide the cache as well.

There are also commerical model available as well that are just as accurate, they are used for surveying and are very accurate, also very expensive.

 

On the Trimble site, the specs (I think something like 10cm) for some of their units require radio base stations within 100 miles. Good if you are a surveyor who works with 100 miles of the station, but not totally portable.

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The military units recieve on an additional frequency. They also have software that will eat through jamming much better than our commercial units. Military units do not have the artificial limits of altitude and speed imposed as our units do. Military units require a daily key to be entered in order to get the accuracy they have.

 

The biggest problem is apart from all the improvements. If you are caught with a military GPSr in your possesion, you get a free vacation in a Federal Prison.

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I'll avoid the discussion in regards to comparing the military vs civilian units capabilities. I will pipe in with the observation that it really doesn't matter what the difference is for the vast majority of users. If you don't have access to the classified encrytion keys, a military gps unit will only function the same as a civilian unit anyway. Even if you might have access to the hardware, and codes, you're not going to have authorization to use the device for games like geocaching.

 

Worth noting is that the military version of geocaching tends to be a little different anyway. When you use a JDAM to sign the log so to speak, it tends to have more impact than a simple internet log.

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Worth noting is that the military version of geocaching tends to be a little different anyway. When you use a JDAM to sign the log so to speak, it tends to have more impact than a simple internet log.

 

Yeah, not only does the military log a "FOUND", but they also have to log a "NEEDS MAINTENANCE"! Boom, Baby! :):D

Edited by rocketsteve
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Worth noting is that the military version of geocaching tends to be a little different anyway. When you use a JDAM to sign the log so to speak, it tends to have more impact than a simple internet log.

 

Yeah, not only does the military log a "FOUND", but they also have to log a "NEEDS MAINTENANCE"! Boom, Baby! :):D

 

No, actually that is a Archived log.

 

Jim

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I was using military GPS in the 90s. The PLGR was about 6"X8"X2". They were a classified piece of equipment back then if they had the code installed. They were extremely accurate. We were doing "geocaching" even back then. We'd hide ammo cans or resupply points in the desert or mountains and set our Troops out to find them on various routes. Going tactical in total darkness we'd often step on the hidden ammo cans. The PLGRs were that accurate. They also had some attachments we could use for range finding with lasers, etc. They did a lot more than your commercial GPSr altho I don't recall any PLGR telling us the prime hunting and fishing times.

I also used Total Station type GPS units for surveying at crime scenes and accident reconstructions. They were accurate to within 2 cm. Not all that convienent for geocaching and not worth the expense. The last unit I bought for my crash reconstructionist was over $25,000 and it didn't have all the bells and whistles.

Edited by Wadcutter
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Each satellite carries two cesium and two rubidium clocks (These are the atomic clocks. They are based on the fact that it takes a known exact amount of time for an atom of cesium or rubidium to decay.)

 

 

Not to be a nit picker, but the atomic clocks used in GPS don't use radioactivity. They use microwaves to set up oscillations between energy levels in the atoms of cesium or rubidium. It's the frequency of the oscillations they are measuring to determine the passage of time.

 

http://en.wikipedia.org/wiki/Atomic_clocks

 

Ken

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Worth noting is that the military version of geocaching tends to be a little different anyway. When you use a JDAM to sign the log so to speak, it tends to have more impact than a simple internet log.

 

Yeah, not only does the military log a "FOUND", but they also have to log a "NEEDS MAINTENANCE"! Boom, Baby! :):D

 

No, actually that is a Archived log.

 

Jim

 

MY BAD!! :lol:

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WASHINGTON (October 05, 2009) - Rockwell Collins today introduced its new MicroDAGR hand-held GPS receiver for soldiers. This latest-generation navigation device, which is a smaller version of Rockwell Collins' highly successful Defense Advanced GPS Receiver (DAGR), brings together the best commercial technologies with the security needed to meet military requirements, and the durability needed to survive the most rugged battlefield conditions. The announcement was made during the Association of the United States Army Annual Meeting & Exposition in Washington.

 

The MicroDAGR provides dismounted soldiers with real-time position, navigation, moving maps and timing information on a full-color touch screen display, and is small enough to be worn on the wrist, attached to a lanyard, or placed in a pocket. The receiver initially features L1 frequency capability, utilizing military only secure GPS signals with anti-jamming and anti-spoofing capabilities. MicroDAGR is also equipped with the latest Selective Availability Anti-Spoofing Module (SAASM)-based anti-jamming software.

 

Designed in response to feedback from soldiers in the field, the MicroDAGR also incorporates several new features including vibration alert, an MP3 player and a digital camera. These features will allow soldiers to record geo-rectified images of the battlefield for after-action review and analysis, listen to foreign language translations of important commands and phrases and get silent alerts from their MicroDAGR when they reach preprogrammed waypoints and/or danger areas.

 

"The MicroDAGR represents a major step forward in delivering a small, lightweight, easy-to-use GPS receiver to the military," said Bruce King, vice president and general manager of Surface Solutions for Rockwell Collins. "We can't wait to get this innovative new system into the hands of our soldiers so they can be equipped with the latest technology for enhanced situational awareness, safety and security."

 

The new system will be available for delivery in January 2010. The first deliveries of the MicroDAGR will go to the U.S. Army Rapid Equipping Force (REF). Through the REF, the U.S. Army will ensure that this important new soldier capability reaches the warfighters as quickly as possible.

 

Rockwell Collins continues to enhance its proven DAGR GPS system to address the needs of a wide variety of users. The company has delivered more than 300,000 DAGR units and more than 1.5 million accessories since it was selected by the Air Force for full-rate production in 2003. The DAGR is considered the military handheld GPS receiver standard for position, navigation and situational awareness.

 

Rockwell Collins (NYSE: COL) is a pioneer in the development and deployment of innovative communication and aviation electronic solutions for both commercial and government applications. Our expertise in flight deck avionics, cabin electronics, mission communications, information management and simulation and training is delivered by nearly 20,000 employees, and a global service and support network that crosses 27 countries. To find out more, please visit http://www.rockwellcollins.com/news/page12013.html

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Victory Mike's explaination seems very detailed and so far as I can tell pretty accurate on how the military grade equiptment works except he left out what the L2 signal is for.

 

Because different radio freqs bend at different angles through atmosphere (think prism or rainbow), L1 and L2 will arrive at your reciever at slightly different times. By comparing the timestamp in each signal and by knowing how different atmospheric conditions affect the each freq the reciever can determine the exact amount of atmospheric distortion between it and each satellite then cancel it out. However, without the cryto data (which is highly illegal for anyone outside the military to have) you can't "read" the timestamp embeded in L2. Civillian GPSr's could recieve it all day long if the makers built them to do so, but it wouldn't do jack for you without being able to decode the timestamp.

 

Also I'm not sure where he got his information on how P-codes work, I've never heard anything on the coding and transmition of them before, but I find it hard to believe it is a 38 week long broadcast signal. First, why would you broadcast your encryption data? Second, satellites come and go all day, even with each satellite broadcasting a different segment it'd take more than a week to get it all because each satellite would only be in view a few hours each day. With a set-up like that even the military would have to leave their recivers on for weeks to get all the data they needed downloaded to the GPSr and then the first time the power goes out or the batteries fail....

 

That said, maybe he's right about the structure of the code, as I said I've never heard anything about the tech specs.

 

AK

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