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

[David]

Gyrators are usually used to create impractical inductances or
frequency dependant negative resistances but I suppose you could.  I
do not think you would gain anything though since you would be trading
one set of non-ideal behaviors for a different set.  This is
especially the case since the non-ideal behavior of inductors is
almost always worse than the non-ideal behavior of capacitors.

For example, you can sometimes avoid large feedback or input
resistances by substituting a T-network but offset voltages and
voltage noise will be multiplied accordingly.

On Sun, 1 Jan 2012 13:52:27 -0700 (MST), "Don Latham"
<djl at montana.com> wrote:

>Aren't there op-amp circuits that create a large capacitance? The gyrator?
>Don
>
>David
>> Jim Williams did this in one of his designs for measuring low
>> frequency reference noise.  The large value low leakage wet tantalum
>> capacitor he used was like $400 and it took 24 hours for the
>> dielectric absorption to settle:
>>
>> http://www.linear.com/docs/28585
>>
>> You can get the necessary time constant using a good 1uF film
>> capacitor with good design and construction in this case.
>>
>> On Sun, 1 Jan 2012 15:11:04 -0500, Bob Camp <lists at rtty.us> wrote:
>>
>>>Any real world capacitor will have a dielecric with an associated
>>> insulation resistance. It's a "more money gets better performance" sort
>>> of thing, but there are indeed limits. A 1000 uF cap that has a "good"
>>> insulation resistance number might cost you more than some new cars
.
>>>
>>>On Dec 31, 2011, at 11:54 PM, Chris Albertson wrote:
>>>
>>>> On Sat, Dec 31, 2011 at 5:56 PM, Hal Murray <hmurray at megapathdsl.net>
>>>> wrote:
>>>>
>>>>> I think the main problem in this area is building a low pass filter
>>>>> with a
>>>>> long time constant.
>>>>>
>>>>> The time constant of the filter has to be:
>>>>> long relative to the noise from the phase detector
>>>>> short relative to aging of the oscillator
>>>>> short relative to environmental changes
>>>>>   (so the osc can track temperature and voltage
>>>>>     those changes may be in the PLL system rather than the osc)
>>>>>
>>>>> If we are starting with PPS (rather than 10KHz), the filter time
>>>>> constant
>>>>> needs to be 10s or 100s of seconds.  How do I build an analog filter
>>>>> with a
>>>>> time constant that long?
>>>>>
>>>>
>>>> Time constant is just R*C.  If you have a 1000uF cap and a 1K
>>>> resistor you
>>>> have 1 second.  In theory you could build 100s just by using a 100K
>>>> resistor but I think real world components are not perfect enough.
>>
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