I've always used the analogy it is like trying to see a candle
flickering at a mile away with one eye while the other has a
flashlight pointed at it from a few inches away. You have to add a
very good light shield divider between the eyes before the brain can
ignore the obliterated eye and see the distant light. The slightest
amount of light into the "dark eye" overloads it and prevents the weak
All the brick wall filtering on the transmitter(s) will have little
effect on the hundreds of millions of "consumer grade" devices with
fairly broad receiver frontend filters. This includes virtually every
cell phone in use today that relies upon GPS to provide E911 centers
with the location of a wireless caller. Miniaturization must still
comply with the laws of physics.
On Mar 10, 2011, at 9:50 PM, K8RI <email@example.com> wrote:
> On 3/10/2011 10:56 AM, Steve Sacco NN4X wrote:
>> You think we have RFI problems! The GPS industry is freaking out about
>> this Lightsquared proposal.
> It should be far more than the GPS industry.
> Almost all transportation from air, rail, trucking, and shipping depend
> on GPS in one form or another.
> The banking and financial industry uses it for highly accurate time
>> After reading the article, check out the links at the bottom of the page
>> to other goings-on about the concerns.
> This affects far more than international flights. Nearly all aviation
> IFR flights over the continental US, General aviation, All current cell
> phones, emergency services, car navigation, shipping within range of
> shore stations, and many things we don't even associate with GPS are
> likely to be affected. Now days GPS affects nearly all phases of our
> lives including the national power grid and even amateur radio.
> The power levels authorized to LightSquared for these ground stations is
> 45 KW, not one KW in a frequency band set aside for satellite service.
> They talk about a transmitting filter, but how well do you think a
> reciver listening to a signal measured in microvolts or a fraction of a
> mircovolt would fare just running next to a *clean* carrier of 45 KW?
> Admittedly that is an over simplification, but OTOH it's pretty much the
> general idea. It's unlikely they can do any thing to a clean signal to
> improve blocking of the GPS signals and LightSquared has already stated
> they believe it's up to the GPS industry to fix the problem.
> Simulations (by Garmin) have shown these signals can block GPS receivers
> for many miles.
> On top of this BTW are the jammers or personal privacy devices of PPDs
> that "intentionally jam GPS which although illegal are widely available.
> Until recently they were available on e-bay in ranges from $30 to well
> over $300 and capabilities from a few hundred feet to miles. A Google
> search on Personal Privacy Devices turned up over 104,000 hits with them
> as cheap as $16.00. Some sites were selling jamers for cell phones,
> WiFi, GSM, and stuff I'd never heard of. Many of these were articles
> about the problem, but many of them were places selling the PPDs.
> One of these, or likely LightSpeed could render APRS useless during
> storm chasing, not to mention the Biz Jet coming in to land IFR at the
> local airport where they are using GPS for both horizontal and vertical
> To top it off, this is being pushed against the wishes of the Department
> of Defense, Department of Transportation, and IIRC the TSA who have been
> told they will participate in the program although I'm not sure what
> participate means unless it's "quit complaining".
> Roger (K8RI)
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