[time-nuts] GPS SDR

Jim Lux jimlux at earthlink.net
Thu Feb 2 05:53:16 UTC 2012

On 2/1/12 12:22 PM, Attila Kinali wrote:
> On Wed, 1 Feb 2012 11:49:51 -0800
> Peter Monta<pmonta at gmail.com>  wrote:
>> One possible inexpensive design:
>> - RF input passively split three ways, with LC filters for the three
>> channels:  L5/E5, L2, and L1/E1/Glonass
>> - For each channel, a downconverter (Maxim MAX2121) feeding a ~65 Ms/s
>> ADC (e.g. MAX19505)
>> - A low-cost FPGA (e.g. Spartan-6) that quantizes the channels to 2
>> bits, does AGC, assembles Ethernet packets
>> - Ethernet PHY, power (PoE?), etc.

You don't need the ADC: you just need a limiter/comparator. But you do 
need a bunch of RF gain.  I think you can get suitable ceramic filters 
off the shelf for the GPS frequencies that are inexpensive.

You don't need insane sampling rates. Think in terms of subharmonic 

> Heh..That's pretty much the design i thought of, though using a higher
> sampling frequency (100 to 200Msps) which would allow to coherently
> decode the E5a and E5b signals together. There is an ADC from National
> that can do 200Msps for 20 bucks, with FPGA friendly parallel output
> (ADC08200).
>> Is there a publically-available antenna design that's easy to
>> fabricate, has a stable phase center, covers 1100--1600 MHz, and has a
>> good pattern over this band with low cross-polarization?  Even a large
>> choke-ring design would be okay if it's fully specified.

I think there are some crossed dipole designs around.  What about quad 

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