[time-nuts] reference oscillator input circuit

John Ackermann N8UR jra at febo.com
Wed Dec 8 13:05:13 EST 2010


I can confirm that -- that's where I found it (and my schematic in the 
TADD-2 manual gives credit to Wenzel)!

I chose that design mainly because it worked over a wide range of input 
levels.

John
----

On 12/8/2010 12:48 PM, Robert Darlington wrote:
> Just an FYI guys, I'm pretty sure the 3rd circuit down on the Wenzel page is
> identical to the input circuit for the TAPR TADD-2 frequency divider.  The
> TADD-2 adds a transformer and load resistor.  Schematic is in the manual
> here:
>
> http://www.tapr.org/~n8ur/TADD-2_Manual.pdf
>
> -Bob
>
> On Wed, Dec 8, 2010 at 8:46 AM, John Ackermann N8UR<jra at febo.com>  wrote:
>
>> Wenzel has some discussion and circuits at:
>> http://www.wenzel.com/documents/waveform.html.
>>
>> The Shera GPSDO made clever use of the input circuit of a 74HCT4046 PLL
>> chip for squaring.
>>
>> John
>> ----
>>
>>
>> On 12/8/2010 10:31 AM, jimlux wrote:
>>
>>> I'm looking for suggestions on a general circuit that can be used to
>>> receive an external frequency reference (nominally a real clean sine
>>> wave at, say, 10 MHz, although up to 100 MHz is possible) and turn it
>>> into a "real clean" square wave. Galvanic isolation is a plus (a
>>> transformer or capacitor would probably do that).
>>>
>>> I was thinking about rummaging through the schematics for test equipment
>>> reference inputs (since they've already "solved" the problem, eh?), but
>>> any other ideas would be welcome.
>>>
>>> I've scanned the archives of time-nuts, and while we have a fair amount
>>> of discussion on how to square up the 1Hz (or 100Hz) in a phase
>>> noise/ADEV setup, not so much on what to do with the 10 MHz. Rick has
>>> commented that you don't want to use a comparator. I have the papers by
>>> Dick, et al, and Collins, as well as all the others.. they tend to be
>>> looking at the low frequency problem, although the analysis is certainly
>>> applicable.
>>>
>>> I don't know that I'm looking for the whole multiple limiting stages
>>> scheme in any case.
>>>
>>> Oh, as far as performance.. Say the need is to not horribly degrade a
>>> good quality crystal oscillator... here's a typical set of specs:
>>> 76 MHz
>>> 1Hz<-90dBc
>>> 10Hz<-110dBc
>>> 100Hz<-120dBc
>>> 1k-100k<-125dBc
>>>
>>> Adevs of the oscillator run from 5E-12 at 0.1 sec, down to 1E-12 at 10
>>> sec, and back up to 2 E-12 at 1000sec.
>>>
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>>
>>
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