[time-nuts] GPS SDR (was: FE-.5680A trimming resolution)
EWKehren at aol.com
EWKehren at aol.com
Wed Feb 1 21:11:02 UTC 2012
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.
In a message dated 2/1/2012 2:47:51 P.M. Eastern Standard Time,
tvb at LeapSecond.com writes:
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.
> 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
> 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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