[time-nuts] GPS lock of the FE5680. Current experiment andquestion

[paul swed]

Bob
LH is attractive indeed, but the total layout for the receiver and such,
plus I learn not a thing from doing that really is the answer. Heck I can
just use the HP3801.

I have already learned quite a bit. How to control the EFC and the range
and such (Tuning sensitivity) Worked with a new D/A converter and I have to
say its really nice. Tried a method thats suitable to an unstable higher
drift oscillator but not useful for a reasonable RB. Yup lots of
learning. So thats the driver.

I have taken a look at the time to voltage methods and also now appreciate
"Interpolation" yes indeed been familiar and certainly read the HP docs on
the 5370 and 5360 counters. But now I really have a reason to dig in.
Still thinking about the sine wave approach of TVC with the limitations of
analog devices sample and hold, or going with a more traditional T to V
approach. 10 Mhz seems to be a tricky region.
I would say the goal of the project is to get the RB under control faster.
Eliminating a sample time of 100K for instance. I really did not approach
this correctly from the start. That is that the RB really is pretty stable.
(I know well known) And the fallout of that effort was the wrong technique
to start with.
Regards
Paul

On Mon, Feb 13, 2012 at 12:19 PM, Bob Camp <lists at rtty.us> wrote:

> Hi
>
> Necessary question now that you see some of what's in the swamp:
>
> Are you sure you want to do this from scratch rather than lock the FE up to
> the 10 MHz output of a TBolt?
>
> I'm by no means trying to say that there's an obvious answer here. Only
> that
> it's at least worth asking the question. To me the big thing that the TBolt
> brings is LH as a debug / checkout tool...
>
> Bob
>
> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
> Behalf Of paul swed
> Sent: Saturday, February 11, 2012 1:04 PM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] GPS lock of the FE5680. Current experiment
> andquestion
>
> Looks like analog devices makes a pretty nice sample and hold chip. A bit
> pricey.
> But can't really work at 10 MC so that would complicate things
>
> On Sat, Feb 11, 2012 at 10:54 AM, paul swed <paulswedb at gmail.com> wrote:
>
> > Getting very interesting.
> > Bob had mentioned just sample the 10 MC sine wave. What I used to do on
> > homebrew Loran C.
> >
> > Thats easier to do because today its nothing to buffer that 10 MC signal
> > to drive a fast sample and hold. This eliminates the ramp circuitry and
> > constant current sources used in the ramp and tempco effects.
> >
> > This all seems to work out reasonably because the 5680s are in general
> > pretty darn stable. (Boy is that a relative term in time-nuts land)
> >
> > Now to dig through the ole junk box for a sample and hold chips. Most
> > likely older and useless. Go hunting at mouser or digikey for modern
> stuff.
> > Hate to have to go to discrete pulsed diodes.....
> > Regards
> > Paul.
> >
> >
> >
> > On Sat, Feb 11, 2012 at 10:33 AM, Azelio Boriani <
> azelio.boriani at screen.it
> > > wrote:
> >
> >> This is the simplest part if a microprocessor can be used: by the serial
> >> port you get the sawtooth correction in nS to be applied to the sampled
> >> data. The sampled data must be converted to nS or the sawtooth
> correction
> >> must  be converted in a suitable sampled data correction. It is possible
> >> even to hardware correct the PPS with a delay line before using it  (see
> >> the already mentioned gpstime.com/files/tow-time2011.pdf by Tom Clarck
> >> and
> >> Rick Hambly).
> >>
> >> On Sat, Feb 11, 2012 at 1:45 PM, Bob Camp <lists at rtty.us> wrote:
> >>
> >> > Hi
> >> >
> >> > Another way to build an analog phase detector...
> >> >
> >> > Next layer on the onion is how to get the sawtooth correction out of
> the
> >> > GPS and into your loop.
> >> >
> >> > Bob
> >> >
> >> >
> >> >
> >> > On Feb 11, 2012, at 12:05 AM, Chris Albertson <
> >> albertson.chris at gmail.com>
> >> > wrote:
> >> >
> >> > > All these different suggestions build down to one thing, the
> precision
> >> > > with which you measure the phase when you sample it each second.
>  The
> >> > > single flip flop will tell you which half cycle. a simple two bit
> >> > > counter made with two '74 FFs tells you which half cycle and with
> >> > > direction.
> >> > >
> >> > > The "best" maybe  is if you let the PPS set a FF and the 10MHz reset
> >> > > it.  The FF's output gates a constant current to a capacitor and
> >> > > charges it to some voltage.  Then you measure that with a 10-bit
> ADC.
> >> > >  This measures the phase to maybe 1%, gives you direction and is
> >> > > pretty cheap to build
> >> > >
> >> > > Let's see if I have the numbers right?  If you check a 10MHz signal
> >> > > once per second with just the FF then you have 1E-7.  You would need
> >> > > 1000 seconds for 1E-10.   But if you measure phase to 1/10th of a
> >> > > cycle you get to 1E-10   ten faster.  Right?
> >> > >
> >> > >
> >> > > Chris Albertson
> >> > > Redondo Beach, California
> >> > >
> >> > > _______________________________________________
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