[time-nuts] GPS Interference Question

Magnus Danielson magnus at rubidium.dyndns.org
Sat Oct 1 18:43:04 UTC 2011

Hi Jim,

On 01/10/11 16:46, Jim Lux wrote:
> On 10/1/11 1:38 AM, Magnus Danielson wrote:
>> On 30/09/11 18:06, Chris Albertson wrote:
>>> One sure-fire "fix" to the problem is to open up the military
>>> frequencies
>>> to everyone. GPS broadcasts on more than just the common L1 freq.
>>> but also on 1.2Ghz.
>>> Again, not really pratical because of the huge cost of conversion
>> L2C is already being roled out, but relying only on that is to early as
>> only 8 birds transmitt it.
>> L5 is also an option in the future. Only one bird transmits it.
> I think there's actually two, but not turned on all the time. Not sure
> though.

They sent one up with a "demostrator signal" which had issues... on L1 

Will check it properly myself as my memory is hazy... seems one of the 
IIF sats (IIF-2 launched in July) has not been brought into 
constellation yet.

>> In a distant future it would be possible to build devices with L2C & L5
>> only. They are so close in frequency that a common RF chain would not be
>> too hard.
> But you lose the ability to measure ionospheric delays as well, when the
> two frequencies are close.

You don't loose it, you just doesn't get the same precision. However, 
recall where we are comming from... not real observation at all but 
approximate models being parametriced.

Still, L1, L2 and L5 would be the ideal.

> L5 is all about safety of life applications, since the spectrum for L2
> isn't protected as well as that for L5.



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