[time-nuts] oscillator choice question

Neville Michie namichie at gmail.com
Mon May 3 01:24:18 UTC 2010


Or you could rotate the whole OCXO on flexible leads through 180* and  
let gravity tune your frequency.
The range might be small, but an occasional tweak on the frequency  
control might be acceptible.
cheers, Neville Michie


On 03/05/2010, at 6:00 AM, Bob Camp wrote:

> Hi
>
> An R-390A (or an not an A) has a lot of examples of how to do anti- 
> backlash gear trains. Pretty tough to do on a one up fab from  
> scratch in the basement basis though.
>
> Lots easier to kludge in a low capacitance tuning diode .....
>
> Bob
>
>
> On May 2, 2010, at 3:54 PM, Bruce Griffiths wrote:
>
>> Bob Camp wrote:
>>> Hi
>>>
>>> A coupe of issues with mechanical servo tuning:
>>>
>>> 1) It wears out the tuning capacitor pretty fast. They are  
>>> designed for a limited number of adjustments. They loosen up with  
>>> a lot of tuning and this degrades their stability.
>>>
>>> 2) It would be much easier to tear apart the mechanical tune OCXO  
>>> and put in a tuning diode than to rig a thermally isolated high  
>>> resolution servo stepper
>>>
>>> 3) Mechanical tune arrangements normally  have backlash. That's  
>>> not an issue as long as the servo only goes one way. It becomes a  
>>> real pain to correct for each time you reverse direction.
>>>
>> One solution to which is to add (in addition to the servo motor) a  
>> torque motor to preload the gear train so that the same flank of  
>> each gear tooth is in contact for both directions of rotation.  
>> Zero backlash drive reduction systems are also available at some  
>> considerable cost.
>>
>>> 4) Making a mechanical setup with a minimum step below 1 ppt is  
>>> going to be more than just a simple stepper. A gear chain based  
>>> system will be pretty exciting to work up. Backlash in the gears  
>>> will add to what ever you have in the tune it's self.
>>>
>>> 5) The tuning on the OCXO may not be monotonic. That's especially  
>>> true if you do indeed run the trimmer at a higher resolution than  
>>> a normal human could adjust it. Tuning reversals tend to drive  
>>> servo loops a bit crazy.
>>>
>>> None of that says that it can't be done. All it says is that it  
>>> will be hard to do well.
>>>
>>> What kind of accuracy are you trying to obtain?
>>>
>>> Bob
>>>
>>>
>> Bruce
>>
>>> On May 2, 2010, at 3:18 PM, chris at yipyap.com wrote:
>>>
>>>
>>>> That is a really cool picture.
>>>>
>>>> Can I be like you when I grow up?
>>>>
>>>>
>>>> I've figured out which of these silvered modules
>>>> in this Schomandl sig gen is the oscillator (the one that
>>>> got warm).  I have to figure out if it is voltage adjustable
>>>> in some way.
>>>>
>>>> Does anyone use mechanical adjustment with a servo,
>>>> gear train and microcontroller?
>>>>
>>>> I did hear all of those good advisers telling me to
>>>> buy the Thunderbolt.  But I already have these pieces
>>>> so...
>>>>
>>>> --
>>>> Chris
>>>> w0ep
>>>>
>>>>
>>>> Niels Lueddecke wrote:
>>>>
>>>>
>>>>> You see? Don't do it, don't even think about starting.
>>>>> Go buy a trimble thunderbolt, it will save you LOTS of time!
>>>>> http://www.dulli.org/pics/20100502%20-%20Clock.jpg
>>>>>
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>>>
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>>
>>
>>
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>
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