[time-nuts] Thunderbolt? (re simple gpsdo.)

[Don Latham]

OTH, if it's an OCXO, then the thermal time constants can be made large
thermos bottles, etc.?
Don

WarrenS
> Chris posted:
>
>>What level of performance did you get?
>
> Correct it depends on what parts you use and how nutty you want to get.
> So much also depends on how you define performance, and where you want
> to
> compromise.
> Compared to WWV and WWVB it was much better, Compared to a correctly set
> up
> TBolt much worse.
> In a "NUT-Shell",  It is good of enough for most any REAL non-Nut
> application.
> Ball park numbers: Freq error of 1e-8 is simple, 1e-9 is easy, 1e-11
> gets
> hard without some good parts and lots of care to details.
> Besides the GPS engine and the Osc, The time period the freq is averaged
> over is an important factor, because of the jitter.
> If you do not loose sync, like all GPSDO, over a long enough time period
> of
> many days or weeks, it is good enough to check and calibrate ANY Osc,
> because it can be set up so that there is NO long term accumulative
> drift,
> just short term freq jitter.
>
>> just one flip-flop, divider and a capacitor.
> AND some resistors
>>I'm looking for a controller that is much more like the bimetallic
>> spring
>>thermostat.
>
> For a Bang bang type two state controller like your bimetallic example,
> you
> don't even need the cap which is added to filter out freq jitter.
> Take out the filter cap, scale and adjust things right and what it does
> is
> if the freq is less than the GPS,
> when the FF toggles it will raise the freq above the GPS and then when
> the
> phase matches,
> it will toggle back and lower the freq below the GPS.
> This will continue forever keeping the AVERAGE Osc Freq dead nuts on
> bouncing back and forth between
> a couple frequencies in what then becomes a PWM like function of the OSC
> bouncing between two frequencies, one higher and one lower than 10.000
> MHz.
> The freq step size and jitter is a function of the resistor divider used
> and
> the EFC sensitivity.
> The PWM cycle rate depends on freq step size, the speed of the PPS
> signal,
> the osc divider used and GPS PPS phase noise.
>
> Lots of other uses for this type of  D FF as a basic ns hi-low Phase
> detector for low freq signals.
> Remove the EFC feedback, Reduce the 100 to 1 divider to two or so and
> you
> can use this to measure and/or  manually set a Rb Osc to be on frequency
> if
> you have an accurate 1PPS signal.
>
> ws
>
> ************
> [time-nuts] Thunderbolt? (re simple gpsdo.)
> Chris Albertson albertson.chris at gmail.com
> Sat Dec 31 20:34:14 UTC 2011
>
> I think this is the simplest design that can still work, just one flip
> flop, divider and a capacitor.
>
> What level of performance did you get?    I think it depends on how big
> the
> integrating capacitor is and how stable the VCXO is.   I guess if you
> switched to using the t-bolt the performance was not as good as a
> t-bolt.
>
>
> On Sat, Dec 31, 2011 at 10:23 AM, WarrenS <warrensjmail-one at
> yahoo.com>wrote:
>
>> Chris
>>
>> Here is a GPSDO I built that better fits Your definition of "Simple".
>> I
>> used this as my freq standard before getting a TBolt.
>>
>> 1) Feed the PPS output of an oncore GPS timing engine which has 1 Hz
>> or
>> better yet 100 Hz output to the clk of a D FlipFlop (74HC74)
>>
>> 2) Feed the FF's D from a 10 MHz osc which has been divided down to
>> 100KHz
>> or less using 74HC390.
>> The FF output shows if the Phase of the Osc is greater or less than
>> the
>> GPS signal and the FF will toggle back and forth when the phases are
>> near
>> equal due to the typical 40 ns jitter on the GPS pulse signal.
>>
>> 3) Add a RC filter to the FF output using a big cap, so the voltage
>> out of
>> the RC filter is 0 to 5 volts depending on the duty cycle of the FF.
>> (A small R in series with the cap will help stabilize it if a real Big
>> cap
>> is used).
>>
>> 4) Feed the filtered analog FF output voltage (No buffering necessary)
>> to
>> the EFC of an 10 MHz osc that has its EFC input desensitized with a
>> couple
>> of Rs and has been set to be real near 10 MHz at the nominal analog
>> FF's
>> 2.5 volts output using the Osc's mechanical tuning and/or add a fine
>> freq
>> adj pot.......
>
> Chris Albertson
> Redondo Beach, California
>
> ************
> snip
> Home heating thermostats can be simple of complex.
> Some use LCD displays and a computer.
> Other have a simple bimetallic spring inside.
>
> But for now I'm looking for a controller that is much more like the
> bimetallic spring thermostat.
>
> Chris Albertson
> Redondo Beach, California
>
>
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-- 
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Ghost in the Shell


Dr. Don Latham AJ7LL
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