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

[Bob Camp]

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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