Quoting Mike Monett XDE-L2G3@myamail.com:

Mike

I did some time ago, for some examples (other implementations are also
possible ) see:

http://www.ko4bb.com/~bruce/LinearPhaseComparators.html

HP used to make the K345991A phase comparator for this purpose.
They also produced other variants for use with their caesium beam standards.

The quickest and easiest is to use the AD9901 phase detector as it
only has a few ns of non linearity at the end of the range. For higher
resolution just add a sigma delta ADC.

The Agilent link link:

ftp://ftp.agilent.com/pub/manuals/

is actually at the bottom of the text at the top of the equipment page
on the hparchive site

Sorry I cant post the site as a link as I am temporarily using a
backup email server as the regular one can't yet find the new time
nuts server.

Bruce

two things i can think of:

1. grab a copy of the trimble planning tools. they're not a web page,
   but they can compute a constellation (and your view of it) at an
   arbitrary place and time.
2. grab a copy of GPSTk. This can also do the calculations, but GUI
   display is up to you.

On Tue, Oct 14, 2008 at 11:12 AM, Mike Feher mfeher@eozinc.com wrote:

--
GDB has a 'break' feature; why doesn't it have 'fix' too?

http://en.wikipedia.org/wiki/Wikipedia:Featured_picture_candidates/Animated_representation_of_the_orbit_of_the_GPS_system

Might give you some ways to start.

There's a raft of GPS surveying planning applications out there that are designed to tell you which s/v are where at what time. It was a big deal back when the constellation wasn't fully filled and you wanted to do precise surveying.  There's also time keeping applications where you're doing common-view time transfer, so there's some applications that will tell you when and which satellites are in view for both ground stations at the same time.

Jim

On 10/14/08 11:39 AM, "Chris Kuethe" chris.kuethe@gmail.com wrote:

two things i can think of:

1. grab a copy of the trimble planning tools. they're not a web page,
   but they can compute a constellation (and your view of it) at an
   arbitrary place and time.
2. grab a copy of GPSTk. This can also do the calculations, but GUI
   display is up to you.

On Tue, Oct 14, 2008 at 11:12 AM, Mike Feher mfeher@eozinc.com wrote:

--
GDB has a 'break' feature; why doesn't it have 'fix' too?

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Mike,

I needed something similar a while ago and ended up with
some animations too:
http://www.leapsecond.com/pages/prn32/

My favorite visual satellite tool is:
http://science.nasa.gov/Realtime/jtrack/3d/JTrack3d.html

/tvb

The calculation I gave is an upper bound on the stability. It relies
on the  resolution.  The accuracy is basically  irrelevant  for this
measurement. Once  the rate of change exceeds about 1/10  degree per
second, it is impractical to record the data manually, and  you have
to go to a different method.

[...]

Those are  all  variations  of an XOR.  This  is  perhaps  the worst
possible phase  detector to use for precision  applications.  It has
very high ripple at lock, which generates unwanted sidebands  in the
PLL oscillator output.

It requires  signals  90 degrees out of phase, so  you  have  to add
extra logic to lock to signals that are in phase. This adds jitter.

The output is not referenced to ground, but to some  floating level.
This means very small offsets and drift will change the lock point.

It is  also unsuitable for measuring phase angle. The  slope  of the
transfer curve for the basic XOR reverses at +/- 90 degrees.  So you
can't use it to measure phase angle.

The AD9901  hase  all  the above problems but it  rails  at  +/- 180
degrees instead. It cannot be used to measure phase angle either.

The standard phase/frequency detector (PFD) is better  for precision
PLL's since  the output signal is zero at lock.  This  means minimum
ripple to generate sidebands. It can be reset to a known state so it
can be  started  in  phase with  an  incoming  signal.  This greatly
reduces the lock time.

It wraps  at 360 degrees, so it is also better suited  for measuring
phase angle.

These are only some of the issues in analyzing a phase  detector for
a precision  pll.  Here is a quickie  LTspice  analysis  showing the
phase detector transfer curves for the three detectors. I  posted it
so people would not get their mailbox clogged with attachments.

http://silversol.net63.net/spice/phasedet/phasedet.htm

[...]

The AD9901  is a very bad design. Probably the poorest  I  have ever
seen. It  is  unsuitable for measuring phase  angle.  Adding  a high
resolution ADC will do nothing to help.

I notice  there is very little in the way of analysis on  your site.
This means it is impossible to distinguish one circuit from another.

What you  really  need  to do is go through  and  put  everything in
LTspice so people can look at the circuit behavior in detail.

Then you need to do a tolerance and sensitivity analysis to show how
stable the circuits are over long periods.

Then you  need to do a noise analysis to show why some  circuits are
better than others.

This would make your information much more valuable and interesting.

One of my big problems right now is trying to understand why the XOR
works so well in one of the GPSDO's in Tom's Allan variance pages. I
can't find it at the moment, but I need to take a very close look at
this design and see what is going on.

[...]

Best Regards,

Mike Monett