[time-nuts] GPS Filter

[Bruce Griffiths]

jimlux wrote:
> On 3/8/11 4:24 AM, Pieter ten Pierick wrote:
>> Hi,
>>
>>> GPS phased arrays aren't new, nor is it necessary to physically steer
>> the antennae within the aray:
>>> http://www.navsys.com/papers/0005004.pdf
>>
>> But would such a system help with the LNA overload due to a local
>> transmitter?
>> I would expect that using separately steered antennas with good
>> directivity could prevent this out-of-band LNA overload?
>>
>
>
> As long as your phasing is done before the one-bit ADC, you can place 
> a null on the offending interference source.  This has been used for 
> adaptive interference cancellers for decades (for cosited transmitters 
> and receivers).  A friend worked for American Nucleonics back in the 
> 80s when they were starting to implement digital control loops (but 
> the cancellation was still done with analog techniques) for this 
> application.
>
> You *might* be able to do it even after the sampler, if the 
> interfering signal isn't too strong.  At a guess, if the total noise 
> power at the input to the sampler were within about 10dB of the 
> interfering signal, you'd probably be ok.  When the interfering signal 
> gets up to 10-20 dB over the noise power, it starts to really dominate.
>
Replacing the 1 or 2 bit ADC typically used with a higher resolution ADC 
may be necessary if the interfering signal is very strong.

This approach is likely to be adopted for the SKA to mitigate 
interference over the very wide bandwidth this telescope system is 
intended to cover.

Bruce