[time-nuts] wwvb 60 khz tuning fork crystals Some insights

Bob Camp lists at rtty.us
Thu Jun 27 20:22:39 EDT 2013


The U / unbuffered inverter has less delay than it's buffered cousin. 

In order to get an oscillator, you need to satisfy Barkhausen's criteria:

loop gain > 1 to start up
loop gain = 1 in operation
net phase around the loop = 0 (modulo 360 degrees)

As long as the gate has more gain than the crystal network (crystal plus caps) has loss, it will start.

As long as the delay through the gate isn't to crazy, it will oscillate with about a 180 degree phase shift on the crystal network, and 180 degrees through the inverter.

In order to start, you want to get the inverter in it's linear region. That's not at all easy with a schmitt trigger. Much easier with a normal inverter. 


On Jun 27, 2013, at 3:09 PM, Hal Murray <hmurray at megapathdsl.net> wrote:

> paulswedb at gmail.com said:
>> Ed good comment on the 74c04. May tinker with that. Though the HC14s working
>> pretty nicely now. 
> They make 74xU04 for many values of x.  The U is for Unbuffered.  They have 
> lower gain in the linear region.
> I thought they were intended to be used for things like this, but I don't 
> understand that area.  Can anybody give me a quick lesson or point me at a 
> good URL?
> -- 
> These are my opinions.  I hate spam.
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