[time-nuts] SDR GPS

Jim Lux jimlux at earthlink.net
Thu Nov 24 09:48:01 EST 2011

On 11/24/11 3:38 AM, Attila Kinali wrote:
> On Thu, 24 Nov 2011 11:19:37 +0000
> Poul-Henning Kamp<phk at phk.freebsd.dk>  wrote:
>> Has any of you played with this:
>> 	http://www.sparkfun.com/products/8238
> I had a look at this (and a few other GPS SDR solutions) back a year
> or two ago and decided that they are either way too expensive or
> do not lend themselves well for time-nutty experimentation and are
> still too expensive.
> I guesstimate that a L1 GPS SDR receiver (SAW filter + LNA + down mixer +
> filter + second downmixer + filter + 8bit 40MHz ADC + FPGA) could be
> build with a budget of 500CHF at single pieces, rivaling the price of
> the sparkfun device you mentioned, while being 1) fully documented
> and 2) could lend itself to tinkering.
> Hence i dont think it's worth buying such a device (unless you are a
> software only guy who sees hardware as a necessary evil).
> An L1 + L2 receiver should be not that much more expenive, but the
> availability of filters for the L2 range is bad (you'd have to build
> one in microstrips) and depending on the exact design of the IF stage
> you'd have to doublicate the L1 path earlier or later for the L2 path.
> Hence i gues, a L1 + L2 reciever should have an additional cost of
> 100-200CHF (to the L1 only receiver)
> 			Attila Kinali

A typical spaceflight multiband design has a LNA and wideband filter up 
front (500MHz) followed by 3 parallel chains of filters and amps 
followed by a single bit quantizer.  You might be able to find those 
ceramic filter based filters, which are reasonably small (Lark 
Engineering and others make these).  If it was a full custom, the 
filters might cost a bit in NRE, but since others are also doing GPS, it 
might be a stock item.

There's an ION paper from earlier this year by Courtney Duncan that 
describes our receiver.

:	Duncan, C.B., Robison, D.E., Koelewyn, C. Lee, "Software Defined GPS 
Receiver for International Space Station," Proceedings of the 2011 
International Technical Meeting of The Institute of Navigation, San 
Diego, CA, January 2011, pp. 982-988.


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