[time-nuts] CGSIC: FW: New NANU 2014090

Jim Lux jimlux at earthlink.net
Tue Dec 16 19:46:27 EST 2014

On 12/16/14, 4:29 PM, Magnus Danielson wrote:
> Jim, Bob,
> On 12/17/2014 01:06 AM, Bob Camp wrote:
>> Hi
>>> On Dec 16, 2014, at 7:01 PM, Jim Lux <jimlux at earthlink.net> wrote:
>>> On 12/16/14, 3:36 PM, Magnus Danielson wrote:
>>>> Paul,
>>>> That is indeed the question. Considering that the signal is better
>>>> supported, I hope the light goes on somewhere. The signals is all
>>>> 1,023 Mchips/s, just a thad different. Should be possible to pull
>>>> off if
>>>> people want to do dual frequency without going full bandwidth.
>>>> Then again, if you are willing to pay good money, you can get it today.
>>> what about one of the software receivers? I would think that making
>>> L2 and L5 filters isn't that tough, so all you need is the back end.
>> ….. and the back end is where all the work is.
> There is a fair amount of work along the full path.
> LNA with some L2 and L5 filters is pretty easy.
> I think you still want to have a correlator baseband processing in say
> an FPGA.

well, yes.. but I don't know if there's any handy open source free cores 
out there for that.

  I do know <grin> of an implementation that does the acq and track in a 
pair of Xilinx 2-3000 parts and does the nav solution in a SPARC V8, but 
it's not open source and it's definitely export controlled.

Seems that what's out there is mostly "record bits" and "postprocess in 
C++ or Matlab" Several textbooks even include it.

> There is naturally stuff to be done on the L2C and L5 modulated signals,
> but it goes in a relatively slow paze so that even modest processors can
> keep up with it.

Indeed.. we do 24 channels (where channel is one PRN at one frequency) 
with a 3 frequency solution without making a 66 MHz LEON2 based SPARC 
sweat too much.

That's why it would be intriguing if someone had the FPGA stuff out there.

It would still be an expensive project, I suspect.  Either you'd have a 
few $50-100 boards that would need interfacing and a lot of time, or a 
$1000 board with less time.

One hopes that in a few years, multifrequency stuff will become available.

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