[time-nuts] I've been thinking about a GPS receiver experiment

Bob Martin aphid1 at comcast.net
Wed Oct 25 23:37:26 EDT 2017


Sorry, my mistake, change that to the former!  I have used DACs that 
were monotonic with decent results but prefer analog loops when the 
time constants are short enough.

Bob M

On 10/25/2017 5:46 PM, Bob Martin wrote:
>    The holdover state is a DAC set to the last value of the analog 
> control voltage that adjusts the oscillator frequency. Some designs
> use an analog control loop and switch the DAC into the control loop.
> Others use the DAC to set the control voltage at all times. This can 
> result in a steps in the control voltage (output frequency).
> I've used both methods and prefer the latter.
> 
> Bob M
> 
> On 10/25/2017 5:30 PM, Mark Sims wrote:
>>>   No, you set up an oscillator so that is why you have that problem.
>>
>> I hooked the two rubidiums together just to see what would 
>> happen.   It pretty much did what I expected... chaos...   the 
>> time-nut equivalent of a naughty schoolboy putting a microphone up 
>> to the speaker of the public address system.  I't's a tough job, 
>> but somebody gotta do it  ;-)
>>
>>
>>>   No, not really. The rubidium would be the real hold-over clock.
>>
>> Symmetricom calls the disciplining state where it can't lock to 
>> the 1PPS signal the "holdover" state.  It's sort of like a GPSDO 
>> holdover state.  Their discipline firmware does let you set the 
>> time constant and damping values.  I tried a little playing around 
>> with them, but never found any settings that worked consistently 
>> well with the LEA-5T.
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