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

[Phil]

Thanks guys. I get the 'adjacent band filtering' problem, so I guess I'm just flogging a stupid, circular argument here: isn't it the job of the FCC to ensure that adjacent band usage doesn't lead to this kind of interference problem? I've already worked out the answer to that. But has no-one the understanding, authority and plain common sense to realise that when (and let's be generous, if) the whole thing goes Hara Arena fountain-of-ordure, somebody who allowed it to happen is going to get a right kicking? I mean, this is one major cock-up that even the general public are going to notice, it seems.

[I am unpopular with administrators at the university where I work for repeatedly suggesting that things will not improve unless some of us stop fixing the problems that they cause.]

Okay then, in the words of Goethe (or was it Schiller?) via Isaac Asimov: "Against stupidity, the gods themselves contend in vain."

Phil M1GWZ



On 12 Dec 2011, at 16:20, Robert E. Seastrom wrote:

> 
> 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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