Oh look. LightSquared have figured out how they'll get around the FCC.

[Robert E. Seastrom]

But to answer Phil's question, the band is immediately adjacent (1525
to 1559 MHz) to the GPS L1 band (1559 to 1610 MHz).

GPS signals are typically -160 dBm at the antenna.  A 1.5 kW (+61 dBm)
transmitter into a 15 dB gain omnidirectional antenna 1km away (96 dB
free space loss) will be -20 dBm at the receive antenna.

Your mission should you choose to accept it is to design a front end
filter that has circa 145 dB of rejection for an adjacent band in that
frequency range and fits inside an iPhone or TomTom within the
envelope allocated for the GPS device.  Someone more skilled in the
art than I will probably nitpick this 145 dB number up or down by 10
or 20 dB in a subsequent email by introducing feedline loss at the
transmitter and/or real world margins necessary to receive the spread
spectrum GPS signal, but that's the scale of the problem you're
looking at here.

A typical small (iphone compatible probably filter) may be viewed here:

http://www.chronos.co.uk/pdfs/cts/cer0005a.pdf

A much larger filter that still has nowhere near enough rejection is here:

http://www.chronos.co.uk/pdfs/gsi/L1FM.pdf

There is a reason that the bands were segmented the way they are in
the international and national regulatory agencies' bandplans.

Payola will not change physics.  Lightsquared's approach is to protest
that they are operating inside their assigned frequency band and blame
the victim (in this case, the receivers).  The problem is not limited
to high precision GPS receivers as some folks have claimed; it affects
pretty much everyone who uses GPS and might be near one of those
40,000 cell sites (where "near" means "within 10km give or take").
This doesn't just mean that your nav system won't work; it means that
civil engineering and agriculture are heavily impacted as well.

-r


Mike O'Dell <mo at 131.ccr.org> writes:

> it was a brilliantly engineered bait-and-switch
>
> Lightsquared bought the assets of a bankrupt company
> that that died trying to do a satphone business on
> those frequencies. that use was perfectly within 
> the original intent.
>
> then, Lightsquared said "Oh dear, we need more coverage
> so we'll put 40,000 1.5KW ground cell sites around the country
> to fill in". then they decided the sat channels would only
> be used for backhaul from remote cell sites.
>
> they expected they could lube-up enough with political payola
> that it could slide through the FCC.
>
> while Lightsquared isn't *directly* effected (yet) by the SEC
> probe, it sure makes the prospect of raising more money much
> more difficult, and they need to raise what is known in the trade
> as a "cosmic buttload" of cash. I assume Falcone isn't writing the
> only check - not when he can get other marks, er, investors to help out.
>
> 	-mo
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