[time-nuts] GPS SDR (was: FE-.5680A trimming resolution)

[EWKehren at aol.com]

Being divorced and no children writing a large check is neither a problem  
nor a challenge. To me the challenge is to find solutions that are 
affordable  and work for every body. Sadly there is very little interest or emphasis 
in this  group on this. An example the $ 10 Loran C simulator that Paul and 
I build and  tested, turning obsolete Loran C Receivers in to high 
resolution frequency  displays. Many other projects off list.
The way I understand it the discussion on GPS receivers, in this thread  
started looking for a solution for the FE 5680A. To look at the proper  
configuration, first there has to be a good understanding of the Rb. Aging will  
determine the update rate of the Rb. Second the choice has to be made if 
digital  or analog frequency control will be implemented. Digital dither or no 
dither.  With out dither we are talking 3 E-13  setability. Enough? Some one  
has to test how the Rb reacts to dither. Right now I se a 4 to 5 Hz control 
loop  in my tests. Analog 1 E -14 is no problem. With aging and step 
requirement a  loop can be defined. Being Rb, it can be a long loop which will 
reduce  requirements of the GPS receiver and most likely issues like 
ionospheric delays  will play a roll. That is the time to ask the question what does 
the GPS  receiver have to be.
All the other chatter should be part of a different thread because it may  
confuse some of the readers.
How many FPGA's are running and can be copied by members?
Many have bought FE 5680 A and have no idea how their individual unit  
performs. I have seen 8 E-10 off frequency.
Bert Kehren
 
 
In a message dated 2/1/2012 2:47:51 P.M. Eastern Standard Time,  
tvb at LeapSecond.com writes:

Chris,

When you're down at the ns level, every ns counts  even more.
There actually a "huge" difference between a UT and VP  and
M12 and ...

Then again, it's not always about nanoseconds. There  are also
issues of power and size, support, supply, price, the  future.
Perhaps also RF sensitivity, feature set, upgrade path for  the
likes of GLONASS or Galileo, acquisition time. Even  RoHS.

Perhaps this doesn't matter for a one-off hobbyist, but if  you're
making kits or products it can become an important factor.

If  you are inclined to experiment, just for the sake of exploring
as many of  us on the list are, then certainly you'd want to get
a u-blox at some  point. It doesn't have to be right away, but it
is a pretty nice, very  modern, ultra compact, timing receiver.

If low cost is the object it's  hard to beat that MG1613S board.

/tvb

> What is it these  u-blox device can do that a cheaper Motorola Oncore
> can't?    Depending on the version the Oncore has for 50 to 5 nS
> one-sigma error  on the timing pulses and can do either 1PPS or 100PPS.
>  Single  unit prices are from $18 to $60 very good documentation is
>  available.
> 
> If the u-blox was somehow much better than a  Trimble thunderbolt or
> Motorola Oncore MT12T I'd buy one even at the  above price.   But
> really these older GPSs are already at  the single digtit of
> nanoseconds level and I don't see room for  improvement except....
> 
> If the L2 band is also  used.   This is the way to get order of
> magnitude  improments
> 
> 
> Chris Albertson
> Redondo Beach,  California



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