The political storm clouds over GPS

The political storm clouds over GPS

The Air Force’s top space boss confirmed Thursday that a proposed new national broadband network partly backed by a Democratic campaign contributor causes “severe interference” to the military’s ability to use the Global Positioning System.

DoD and federal witnesses told a House panel on Thursday that they won’t let the new network begin operation until they’re confident it won’t interfere with the military’s GPS, but their appearance came after a report in the Daily Beast that the White House had pressured the head of Air Force Space Command, Gen. William Shelton, to change what he planned to tell the subcommittee. Republicans appeared ready to use the connections to try to embarrass the White House.

Here’s the backstory: Virginia broadband startup LightSquared wants to build a new national network with both terrestrial transmitters and links to satellites in orbit. But the network operates so close to the spectrum used by GPS that it hampers military receivers’ ability to get the precise timing and tracking data they rely on. The Federal Communications Commission gave LightSquared preliminary permission to begin testing its network, and DoD tried it out earlier this year down at White Sands Missile Range and Holloman AFB, N.M. The results, Shelton and others said, were clear: LightSquared’s signals effectively jammed the military’s GPS receivers with their much stronger signals.

GPS, Shelton told lawmakers, was supposed to occupy a “quiet neighborhood” in the electromagnetic spectrum. “But if you put a rock band in the middle of that quiet neighborhood, that’s quite a different circumstance,” he said.

No one disputes the results of this year’s tests, including LightSquared, the House witnesses said Thursday. The company has submitted an alternative proposal that would enable it to use frequencies a little farther away from GPS, and to develop “filters” to protect GPS receivers. That’s where the process stands now; DoD and federal authorities say they haven’t had time to study the new proposal to determine what to make of it, but there’s some worry that the nature of LightSquared also would interfere with GPS no matter what changes it makes.

Complicating all this is that LightSquared is owned by an investment group run by billionaire Democratic donor Philip Falcone. In Thursday’s story in the Daily Beast, Eli Lake wrote that it appeared the White House tried to pressure Shelton to change what he planned to tell the House subcommittee in deference to Falcone’s interest in standing up LightSquared’s network.  Wrote Lake:

The Obama administration urged Shelton to say “the general supported the White House policy to add more broadband for commercial use; and that the Pentagon would try to resolve the questions around LightSquared with testing in just 90 days. Shelton chafed at the intervention, which seemed to soften the Pentagon’s position and might be viewed as helping the company as it tries to get the project launched, the officials said.”

Shelton didn’t give that testimony to the House Armed Services Committee’s Strategic Forces subcommittee; he told committee members unequivocally that LightSquared’s network jammed the military GPS receivers “and to our knowledge, there are no mitigation measures.” Subcommittee Chairman Rep. Mike Turner of Ohio vowed to refer the situation to Rep. Darrell Issa, chairman of the House Oversight and Government Reform Committee. Turner also said that FCC Chairman Julius Genachowski’s decision not to show up for Turner’s hearing was an “affront” to Congress.

So — still hanging in there? It’s a perfect scandal for Republicans: Even as GOP defense advocates rail against what they call dangerous proposed budget cuts for DoD from the White House, now they have a situation in which the Obama administration may have tried to help clear the road for  a big fundraiser whose business could jeopardize military readiness. It fits the classic Republican narrative that Democrats don’t get defense.

The Office of Management and Budget told Lake there’s nothing unusual about vetting government witnesses’ testimony, and Shelton didn’t tell lawmakers what he was reportedly being pressured to say. In fact, in response to questions from Turner and the subcommittee’s ranking Democrat, Rep. Loretta Sanchez of California, Shelton said it could cost billions of dollars and a decade or longer to develop the “filters” needed to safeguard military GPS receivers from interference from LightSquared — assuming its alternative plan actually works as advertised. That’s a non-starter in Austerity America, and Turner asked rhetorically why the military should have to absorb the time, costs and inconvenience to shield itself in the first place — it has a right to continue using GPS as it is, he argued, not an obligation to accommodate private-sector newcomers.

What comes next? Maybe another House hearing, if Issa takes up this cause, and possibly more from the Armed Services Committee when DoD and the feds finish their next round of testing on LightSquared’s alternate proposal. With all the politics and money tied up in this thing, it’s going to come up again.

Join the Conversation

Remember the old joke commercial about margerine where the punch line was “Its not good to fool with Mother Nature!”

Well, this just demonstrates that the laws of physics are not subject to political influence EVEN if the spectrum allocations might be! If you have a very weak little signal with a somewhat uncertain frequency (because of doppler effects) you have to use a pretty wide filter and a very sensitive receiver to find that little bitty signal, particularly if that little bitty signal source is a long way off, geographically.

If you have some high power RF source physically close and also close by in frequency, spread way out because of high bandwidth modulations, you swamp the little signal’s receiver. Mother nature and the laws of physics are satisfied, but the little signal is jammed! Thats about as basic as it gets, and its totally immune to the dollar value of one’s political contributions!

Here is the bigger question, whats to stop other governments especially our enemies from building exactly what lightsquared was working on?

There is no scandal.

The military have been reliant on spectrum that hasn’t been allocated to them is the problem. Now LightSquared has bought it and the military are playing their usual role as bad spectrum user by claiming their problem is LightSquared’s.

We see this every 10 years and every time the whitehouse has to tell the pentagon to get it’s act together and deal with it. If the pentagon had it’s way every other time, there would be no digital mobile phone system, no wifi.

The DOD is notorious for taking over and using spectrum that isn’t theirs, causing interference in all kinds of ways. That being said, Lightsquared better make sure their stuff doesn’t mess with GPS signals before rollout.

The DoD has a radar, radio, or some other system that uses such and such frequency range, but something new comes along to interfer. The RF spectrum is the sovereign property of the nation in which it resides. That’s been international law for about 150 years. Our government sells spectrum to organizations and corporations all the time. That’s their right and the government usually makes a lot of money in the deal. The DoD usually gets it in the shorts and has to redesign a system to accomodate. Economics and national security are constantly struggling with this issue. As itfunk pointed out, wifi, 3G, and 4G used to be military frequencies. In this case, Lightsquared has the ability to seriously interfere with most of our military hardware. Any idea if it’ll interfere with civilian GPS too?

Sorry General,
I have to agree with Lighsquared’s position. These frequencies have been “off-limits” to to non-DoD for so long. They never took advantange of the time or the space. The DoD could have used Cesuim atomic clock crystals in the GPS’s themself, but instead ignored what needed to be done and kept these legancy door stops funded. Remember that req’t called WGS-84 so many moons ago, that was real and there was a real need. And the Spectrum analysis that each program is required to produce for JITC (DoDI 6212.01… that was real and there was a legit need.

Now the DoD cry’s wolf and says it has the rightaway. Why because they sat on a topic, they refused to budge from, now they are forced to defend it, all they do it pay someone off to block it, until the problem goes away. How do you expect to pinpoint military accuracy of the kill when your still using legacy technology and refuse to adapt to technology? Please .… gimme a break, move on to another battle, this one is the one you can’t win!.

A similar thing happened nearly fifty years ago. The DoD invented and fielded an Identification, Friend or Foe (IFF) system. When the FAA wanted to implement the current Air Traffic Control (ATC) system, the military agreed to share the same frequency so as to preclude very expensive retrofits to all military aircraft (if the FAA IFF system employed different frequencies). Years later, whenever the military wanted to change or upgrade their military IFF system, they had to get the approval of the FAA, which routinely blocked these changes due to perceived frequency interference.

How on earth has the military been reliant on spectrum that hasn’t been allocated to them?

LightSquared is cheating.

They were given a license to next to the GPS bands for frequencies that are designated for satellite communication: I.E. to and from satellite using highly-directive antennas (a dish), and using very weak signals from satellites thousands of miles away.

LightSquared realized that they couldn’t make the physics work to get nationwide broadband via satellite, so they asked the FCC for permission to use land-based repeater stations. Except now the plan has very little reliance on satellite and depends on 40,000 repeater stations. On frequencies that were not originally licensed for high-power omnidirectional transmissions.

So when the military, as operators of the GPS system, complain that LightSquared is putting interfering signals on adjacent frequencies that, by international agreement, shouldn’t be there, they are the ones in the wrong? Anyway, who better to complain about interference that is going to affect every user of GPS in North America? Its not just the military who is affected — every airplane, vehicle, farmer, surveyor, UPS driver, etc.

The FCC assigns spectrum and licenses users, but the federal government pre-empts the FCC — that’s how the law is written — unless its the military, then they take it in the shorts.

LightSquared will not be able to avoid causing interference to GPS until they move to another frequency. The physics of this universe just don’t work any other way.

LightSquared wipes out *every* GPS receiver within two or three miles of one of their 40,000 proposed transmitters.

LightSquared complains that if GPS receivers had been built according to the original specifications they would have the necessary filters and there wouldn’t be interference. Hogwash. If LightSquared was using their licensed frequencies for the assigned use (satellite communications) that would be true, but no amount of filtering will make it usable. Its like putting a car crusher in the middle of a hospital: there really isn’t anything you can do to the car crusher to keep the noise from bothering the neighbors, except to move it far away.

Either you don’t know what you’re talking about, or you’re a shill for LightSquared.

Existing users of licensed spectrum trump the rights of new comers. That’s the law. Every GPS user is already grandfathered in. The FCC should have rejected LightSquared’s application when they moved from satellite to land-based repeaters, but LightSquared has been using their political influence to corrupt the lawful process. See my reply above about the original allocation of LightSquared’s frequencies for satellite use only. That is an international agreement with the ITU, not just the FCC.

“cesium atomic clock crystals”?? What? The GPS receiver requires the GPS satellite to send it the time signal as part of the navigation calculation. Putting an accurate clock in the receiver would do absolutely nothing to improve the interference issues.

A cesium clock is quite large and requires a lot of power to operate, so that rules out many uses of miniature GPS receivers. Even the GPS satellites don’t use cesium clocks, they use rubidium, because the lower long-term stability is acceptable. A cesium clock isn’t any more accurate than a rubidium clock in the short-term, and the GPS satellite clocks have to be updated frequently to account for orbital variations, so a cesium standard doesn’t help anything.

The problem is not clocks, its filtering, and you just can’t make sharp enough filters to protect GPS from LightSquared without a physically large design, which again wipes out miniature receivers and increases the cost astronomically (pun intended).

wifi? If you’re talking about 2.4Ghz wifi, that was assigned as an industrial scientific and medical (ISM) unlicensed band decades ago when microwave ovens first came out. Meaning that any user has to accept interference caused by any other user on the band — there are no licenses, therefore no protected users.

2.4Ghz happens to be the the most efficient frequency for heating water, which is why its used in microwave ovens. (The microwave magnetron causes the water molecules to vibrate, creating heat by friction at the molecular level. ) An old, leaky microwave oven will wipe out any nearby user of the 2.4Ghz band, so it was assigned as an unlicensed band.

So I don’t think wifi helps your argument here.

Excellent explanation. The only way to avoid the interference is large filters, which are impractical given the miniaturization everyone has come to expect from GPS receivers.

First, the spectrum was allotted to GPS and sattelite communications. And its not just the military, in tests every GPS signal was jammed within 2nm of the tower and precision receivers for things like surveying, aviation navigation, and agriculture were jammed up to 20nm from the tower. So no cellphone GPS, no navigation systems in cars, no dog trackers, etc, basically anywhere in the entire country. And of course, it is pretty sure that Gallileo and all othersattelite navigation systems are also toast as they use the same frequency.

Second, the band was licensed to LightSquared for a sattelite communication system, but then the FCC ammended the license to include terrestrial based broadband application. So basically LightSquared bought the spectrum at a fraction of the cost, and then the FCC made it extremely valuable by changing the license and giving it to LightSquared for free. And of course, since the FCC Chairman refused to testify, no one could ask him why he approvedthe change in the first place against the opposition of the military, aviation community, and everyone who relies on GPSt, very convenient for the WhiteHhouse don’t you think?

This is obama playing politics with our lives so he can get his big labor backers. He is desperate and will do anything to undermine our military and safety and security of our country. This is a dangerous precedent no matter how you look at it.

“Reliant on spectrum that hasn’t been allocated to them”?

LightSquared got a license for spectrum assigned to satellite communication. That spectrum is right next to the GPS band, and is assigned to satellite communications to protect GPS users — military and civilian. LightSquared tried to build a nationwide broadband system with it, but couldn’t because of the limitations of what they bought — satellite signals are real weak and don’t provide indoor coverage. So they applied for a waiver from the FCC to build land-based repeaters — 40,000 of them. The FCC, because of political influence, gave them a provisional waiver. So far they haven’t been able to avoid creating interference, and I don’t think they can at all.

All the nationwide spectrum for broadband has been sold, allocated, and assigned. LightSquared is trying to sneak in the back door — something the FCC should have denied their application for in the first place.

That’s cheating.

Then they complain that the big bad military is preventing them from making beellions. Never mind that it destroys everyone’s use of GPS on the whole continent.

That’s the scandal.

Nope, physical size has nothing to do with it, it’s the width of the required electrical pass band.

Already have! Google Korea gps.

Ok. In any case, building a sharp enough filter is impractical — which I doubt is even possible. And it shouldn’t be the burden of every GPS user or owner to have to retrofit such a theoretical impossibility on their existing equipment.

Do you understand the difference between frequency and bandwidth? And the effect on bandwidth when you modulate a signal? Don’t feel too bad, whoever approved the application at the FCC didn’t either. (Or unlike the AF general, they allowed their expertise to be bought!)

Sorry, DoDengineer, but in what field of engineering do you have your degree?

Can you please explain to me what happens to a clean CW signal when a high bandwidth complex modulation(as per “4G” cell phone protocols” is applied? And can you explain why all gps users, DoD, industry, and private are up in arms? And why the FCC, charged with controlling spectrum could not answer the same question I asked of you? :-)

This story will be an inside the beltway story unless it is a Pay to Play racket. The public will easily understand payoffs for favors, not so much radio frequencies and interference. There are hints of Pay to Play involving people very close to Obama. HuffingtonPost had an article linking longtime Obama supporters, if not Obama himself to Lightsquared, see here: http://​www​.huffingtonpost​.com/​t​h​e​-​c​e​n​t​e​r​-​f​o​r​-​p​ubl

And guess who complained about making ISM ?

>and is assigned to satellite communications to protect GPS users

simply wrong.

the great irony is tat you have got it the wrong way round. Turns out that the military have been using adjacent unallocated channels to send out terrestrial correction codes and these will get hammered. And I suppose the dime store GSP receivers that are wide open.

“LightSquared wipes out *every* GPS receiver within two or three miles of one of their 40,000 proposed transmitters.”

If that’s the case, then maybe Garmin, Verizon, and all the other commercial GPS carriers should weigh in.

Please provide a reference for that, because I do not believe that you are correct.

They are, and they have submitted their negative comments to the FCC.

“Nothing can stop others from building GPS jamming devices” , is the answer Steve.The more dependent we make our military on GPS based systems the more vulnerable we become to simple jamming or by the destruction of GPS satellites.

The Lightsquared system HASN’T EVEN BEEN BUILT YET, why should DOD, Verizon, AT&T, DeLorme, Magillan, Garmin, and other GPS users and producers have to redesign their products to accommodate Lightsquared?
Think about this: many automobiles on the market today have GPS navigation built-in, aircraft autopilots use GPS to navigate; if Lightsquared is allowed to proceed ALL those receivers will have to be replaced.
There is no way to block out a strong signal and allow a weak signal to come through, THAT’S PHYSICS.
The supporters of Lightsquared are asking every person that owns a GPS receiver (auto-mount, boat-mount, handheld, etc.) to spend their money to replace their receivers. Is Lightsquared going to pay for that? OF COURSE NOT!
TThe Lightsquared system needs to be stopped NOW!

In the GPS band Lightsqured isn’t the stronger signal.

Do you perhaps understand WHY a GPS must have adaptive filters? Until the receiver “knows” where it is, and what time it is, in fairly precise terms, it has no way of knowing if a GPS transmitter satellite is “approaching” or “receding”, and certainly not how fast. The “filters” have got to be wide enough to cover an up-doppler and a down-doppler signal during the acquisition phase. If you have a wide filter, the receiver will integrate all signals within the pass band. For GPS this includes the GPS signals themselves, AND the background noise, AND the “splatter” from the LightSquared transmitters. Add all of those noise sources to the GPS signal and the result is such that you just get a “dull roar” at the detector. If you cant pull the GPS signal out of the noise, the receiver never gets the first position information or timing information that would allow the filters to be sharpened. No sharpening of the filters, no ticky the watchy! Sorry to get technical on that last! ;-)

Wow talk about wrong on all points

1) Lightsquared is not using GPS spectrum the opposite is true. GPS users want to prevent the lawful use of spectrum that was never allocated to them.

2) He is talking about the clocks in the satellites not the receivers lol

3) the size of the filter has much more to do with the frequency being filtered not it’s sharpness. The problem is added expense and some reduced sensitivity not size

Why are you arguing that GPS receivers already has the filtering necessary lol.

this is the master plan full command and control to late to stop it . can only defund it

Im making the point that the filters currently used by GPS receivers are in fact the filters required.… for GPS to work. Change those filters significantly, as would be necessary to filter out the “out of band” modulation products from the LightSquared emissions, and GPS will not work. A filter, either physical or DSP implemented, that would “filter out” the interference will also “filter out” the GPS signal. Its basic physics and mathematics, not politics nor a DoD power play. Should I bother to point out that there are a LOT of other GPS users that would be effected by LightSquared’s implementation?

The problem arises because a spectrum user, LightSquared, was sold rights to spectrum that, because of the specific modulations that LightSquared is planning to implement, trashes the GPS band. The simple explanation is that a bureaucrat at FCC did not understand the physics of modulation and bandwidth (and that is scary enough in its own right!), and approved the allocation. The more troublesome answer is that the bureaucrat was quite possibly told to approve the allocation by his bosses, and in his own self-interest, shelved whatever expertise he had.

If you want a fair topic for discussion, consider that we were all TOLD that GPS was immune to jamming and interference when the system was being fielded. Given those assurances, we have come to base a multitude of other systems on the constancy and invulnerability of positioning and timing data from the GPS network. Now, we have such things as GPS– guided weapons and GPS-based, civilian air traffic control systems (ADS-B). Our computer networks and cell phone towers pick up their timing data from GPS receivers and our cell phones tell us where we are on dark nights. NOW, we have an FCC-licensed commercial entity, LightSpeed, and potential enemies (even technological powerhouses like N. Korea!) that dont put much faith in FCC decrees, who can take down this vital service.

Sad. Very sad.

Electronics. I was an EW specialist supporting the AF and the Navy. Didn’t think I really needed to explain the Nyquist Theorem and ROYGBIV. If you tighten up the lobes, the frequency is clearer. Thus the Cesium in the satelites. Then once the true frequency is captured, you will find there is a lot of slop for Light Squared to maintain a living on. Then you can develop the filter. That alone should take another 3–4 years, DoD rate, 1–2 Commerical. And NO I am not a LS employee.

A little more gasoline for the fire.… . :-)

Here is a curious one for the doubters…. http://​www​.spacenews​.com/​s​a​t​e​l​l​i​t​e​_​t​e​l​e​c​o​m​/​1​1​0​725

In spite of the politically correct bashing of GPS system designers, its interesting that the Europeans, who are actually focusing on a separate but related satellite-based geopositioning system, have also sent in a “friend of the court” briefing! It would appear that at least in some places, people in regulatory positions, are requied to understand that thing that they regulate! But, here in the US where money and partisan politics are all-important, rather simple electrical engineering principles and laws of physics have got to be “negotiated”!

I wish that it kind of thing was only a sad statement about the rigor of our technical educational institutions, but I doubt that more education would have helped in the least!

All of you fly on commercial aircraft right? You have flown in bad weather right? DO you want the pilots of you next flight to look at a red X where their approach information should be. This is not just a military issue.

I had missed the part about the FCC Chairman refusing to testify. . That’s big! . . Hmmmmm. ’ Tis a troubled web we weave….… . . I do believe that the Congress has the right to issue a subpoena. and I cant see a federal official asserting the Fifth with respect to his official duties, at least not and get away with it! :-O

Stated as you have stated it, I could almost believe that the Chairman got caught between the political issues and the physics, and sadly may not have realized that he and his decision would not get by the harsh reality of physics. Now he either has to admit to bowing to the political pressure or admit that he just did not understand the physics, or more likely both! Im absolutely certain that I would not want to testify to Congress on either point.

I used to work at FCC. Generally existing users had priority over new applicants for contested frequency use.
Seems things have changed.
I’d still hope that millions of GPS usersand significant existing and expensive infrastructure would have priority over a new applicant expecially where lives and safety are at stake.
Jamming our GPS I could expect fromour enemies…not from ourselves.

The article is partially incorrect where it says ‘…backed by a Democratic campaign contributor…” the person in question, who is never named in the article, is Philip Falcone and he is also a Republican campaign contributor. In fact, in the past 4 years he’s given more to Republican political campaigns then Democratic ones.

The real issue here is that if the new technology intereferes with national security, don’t allow it or have the manufacturer move it to another place on the electromagnetic spectrum.

Be careful before you get too carried away with bashing Lightspeed! It could easly be another one of these liberal-backed companies that’s been given a huge loan guarantee.…. they might go bankrupt like Solyndra leaving us holding another $540M bill, thanks to our current government that insists on throwing away our hard-earned money.……!

This will probably end up being settled in court; with judges who have even less technical knowledge! :/

Actually, I’m afraid you’re the one who’s incorrect.

From the NTIA Red Book (Spectrum allocations) worldwide
1525-1535MHz — Primary users (in CAPs) are SPACE OPERATION and MOBILE SATELLITE
Fixed operations (which is what LightSquared would be) are not primary or secondary in the band, and must not interfere with primary or secondary operations in the band.

1535–1559: Mobile Satellite Operations (no fixed allocation at all)

So, I’m afraid that the FCC had no legal basis for issuing even a provisional license. Why doesn’t anyone ask the FCC why they violated the ITU, which has the force of treaty?

I’m not sure why people think the military is using public spectrum. The spectrum the military uses has been allocated for years. The government tends to sell off small chunks to help right their wrongs the last one being in the Clinton years where all of 45 Megahertz was sold for $40B, that”s billion, of military spectrum. Someone said this very well above. Lightsquared’s system will affect the public sector much more than the military as GPS receivers are in cameras, cars, boats, planes, and child locaters to name a few. My experience is the military develops technology and components in their allocated frequency bands. Commercial companies force them out after the difficult work is done by paying a small fraction of the total cost to buy the spectrum from the government. This forces the military into higher, more difficult bands to communicate in, causing taxpayers to pay once again to develop new technology and components. Why not get the commercial companies to foot the bill to develop the higher bands instead of using their political clout to get you and I to foot the bill. I know, we would foot the bill anyway but only the ones that would use the technology. The way we do it now everyone pays since the military must develop it.

(1) In the above article Philip Falcone is names is names as the owner of Lightsquared. (2) I do not care about who contributes to who — the point is if it interferes with our military then scrap the program, period! (3) If political considerations play into this due to “who knows who” then heads need to role. (4) All of the posts above are correct in that even politicians can not legislate the laws of nature.

Thats why I prefer the old system, give me a map and a compass any day as back up. You can block the GPS all you want…I will still find you.

If it isn’t then why is LightSquared’s signal interfering with the GPS receivers?

See this article written by a radio engineer: http://​radioworld​.com/​a​r​t​i​c​l​e​/​g​p​s​-​s​y​s​t​e​m​s​-​t​h​r​e​ate

40,000 repeaters at up to 15,000 watts — that’s more power than a whole GPS satellite, much less the signal output received by the GPS receiver 6,000 miles away.

The issue is WHY new technology was allowed to interfere with national security — was it political interference? According to research by Michelle Malkin, the evidence of political interference and cronyism are incontrovertible: http://​michellemalkin​.com/​2​0​1​1​/​0​9​/​2​1​/​l​i​g​h​t​s​q​u​a​red

The isssue is WHY was a technology allowed to interfere with national security? According to research and evidence documented by Michelle Malkin, the existence of political interference and cronyism is incontrovertible. http://​michellemalkin​.com/​2​0​1​1​/​0​9​/​2​1​/​l​i​g​h​t​s​q​u​a​red

The Lightsquared signal sources will be located at most a few hundred miles from the notional GPS receiver ( the horizon from an aircraft for example), while the GPS transmitters will be located on a satellite in a “high, non-geosynchronous” orbit, thousands of miles away. The Lightsquared signal is much higher power (several orders of magnitude) and widely spread because of the high bandwidth modulation and there generally will be more than one LightSquared transmitter within the horizon radius.

Aside from all that, for normal, high probability, signal detection in a noise background (the LightSquared signal looks like broad band noise to a GPS receiver) you need a signal to noise ratio of between 7 and 10. Its a bit more complicated with digital modulation, but just for a starting point, use the analog values. Because the GPS signal from any given satellite moves around a bit because of Doppler effects, probably the 10 value is more appropriate. A little splatter on the LightSquared signal goes a LONG way to screw up GPS.

Roger that in most every detail! … -.- … -.- :-)

Here Am I.…… Kilroy was here.

NOTE: Comments are limited to 2500 characters and spaces.

By commenting on this topic you agree to the terms and conditions of our User Agreement

AdChoices | , and join us on Google+
© 2015 Military Advantage
A Monster Company.