[time-nuts] GPS SDR

[Attila Kinali]

On Wed, 01 Feb 2012 21:53:16 -0800
Jim Lux <jimlux at earthlink.net> wrote:

> You don't need the ADC: you just need a limiter/comparator.

Yes, but this degrades sensitivity quite a lot.

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

This requires that you have an ADC that has the anlog bandwidth of
the signal. And ADCs with a analog BW in the GHz range are damn expensive
and hard to get.

Also a problem is to get the sampling frequency right if you want to
sample more than one band. Downmixing solves both of these problems
at the cost of higher complexity and a bit more noise.
 
> >> 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 
> helix?

Crossed dipole are narrow band and not easy to build as dual band designs
at least at those frequencies. Quad helix needs quite a precision to get
the right frequency and dual band designs (stacked helixes) get even more
difficult. 

				Attila Kinali

-- 
The trouble with you, Shev, is you don't say anything until you've saved
up a whole truckload of damned heavy brick arguments and then you dump
them all out and never look at the bleeding body mangled beneath the heap
		-- Tirin, The Dispossessed, U. Le Guin