[time-nuts] DTV tuner chip usable for GPS front end?

[Jim Lux]

On 3/21/12 9:58 AM, David wrote:
> On Wed, 21 Mar 2012 16:40:27 -0000, "David J Taylor"
> <david-taylor at blueyonder.co.uk>  wrote:
>
>>> I suppose there is limited interest in homebrew GPS receivers given how
>>> cheap the fully integrated chipsets are. However, just noticed the below
>>> tuner chip intended for DTV, actually lists GPS L1 as an applicable
>>> frequency.  A TV Tuner USB stick using this chip is available for $20,
>>> and some SDR type software is apparently working with it:
>>> http://sdr.osmocom.org/trac/wiki/rtl-sdr   Has anyone here played with
>>> this device?
>>>
>>
>> .. and available ready built here:
>>
>>   http://www.funcubedongle.com/
>>
>> but perhaps not fast enough for you.
>
> Or not wide enough in this case.  The FunCube technical FAQ says the
> bandwidth is about 80 KHz as it is designed for narrow band reception
> only and accessed as a standard USB sound device.  I do not quite
> understand how 96 Ksamples/sec yields 80 KHz though:
>
> Q. What is the bandwidth?
> A. 96kHz is the quadrature sampling rate. Once the ADC’s decimation
> filter skirts have been taken into account, you have about 80kHz.
>


I+Q gives you 192 ksamples/sec total.. Plenty for the 80kHz BW.


Maybe you could tap off the output before the ADC and run it into 
something else.

Realistically, though, it would seem that some sort of harmonic sampling 
scheme like JPL used in the radio flying on the SCAN Testbed would work..

Filters for L1, L2 and L5, lots of gain, single bit threshold at the 
end. Sampled at 38.656MHz.

Pretty darn simple RF chain, and all the hard work is done in a FPGA 
hanging off the bits.