[time-nuts] Ultra High Stability Time Base Options for 53132A

Bob Camp kb8tq at n1k.org
Sun Apr 12 21:53:36 EDT 2015


Hi

The fuzzy blob would appear to be an LM361 “high speed (20 ns)” comparator.

Surely it must have a jitter below a couple of nanoseconds :) Even that is only a guess
since jitter is never mentioned in the spec sheet I dug up:

http://www.ti.com/lit/ds/symlink/lm361.pdf

Bob

> On Apr 12, 2015, at 7:48 PM, Richard (Rick) Karlquist <richard at karlquist.com> wrote:
> 
> 
> 
> On 4/12/2015 2:22 PM, Magnus Danielson wrote:
>> Hi,
>> 
>> The buffer transistors has not AC-bypass of the emitter resistance, so
>> that the DC current becomes large and thus contributes flicker noise.
>> 
>> The comparator at the bottom isn't doing a beutifull work of squaring
>> things up without contributing noise, considering the sine output of the
>> 10811.
>> 
>> Was that it, Rick?
>> 
>> Cheers,
>> Magnus
>> 
> 
> The resolution of page 13 is poor, and it seems to be a bitmap instead
> of a vector file.  The fuzzy thing in the lower right corner looks
> like it might be a comparator.  I think this was the smoking gun.
> 
> There was a saying by H.L. Menken to the effect that for every
> complex problem, there is a simple, obvious, invalid solution.
> 
> Squaring up a 10811 with a comparator is a perfect example of this
> principle.  Non-time-nuts always seem to gravitate to this design.
> 
> Of course you're right, any comparator will add jitter to a 10811.
> The faster they are, the more jitter they add.
> 
> I noticed that the standard 10 MHz oscillator is built with
> an ECL line receiver.  Another example of Menken's saying.
> This is a TERRIBLE oscillator design, but one that would appeal
> to the non-initiated.  I built one of these oscillators in 1976
> at the suggestion of my boss.  After seeing how bad it was, I
> quietly designed it out and never used it again.
> 
> Rick Karlquist N6RK
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