[time-nuts] Divider circuit for Rubidium Standard

[Richard (Rick) Karlquist]

On 1/9/2016 12:44 PM, Attila Kinali wrote:

> The purpose of the input circuit is to convert the RF input signal
> into a low-jitter square wave that can drive the PIC clock input.
> The circuit is closely based on the one published by Wenzel at
> http://www.wenzel.com/documents/waveform.html, with modifications
> suggested by Bruce Griffiths and Ulrich Bangert. The revised circuit
> works with inputs as low as -20dBm.

This circuit is very similar to one that was championed by Tom
Faulker of HP/Agilent at the now closed Spokane site.  Tom
measured the circuit at about -171 dBc/Hz.  He was very knowledgeable
about this topic, so we can believe the number.

This is good, because the cited Wenzel document would give me
no confidence whatsoever if that was all I had to go on.  It
reads like it was written by some marketing guy (as opposed to
R&D) who knows just enough to be dangerous.  Other than the
circuit in question, the rest of the document is full of
unreliable information.  Such as how line receivers make great
sine wave to square wave converters.  They are terribly noisy.
IE, the document contains a kernel of truth.  It also has no
quantitative information about the circuit in question or
any other ones discussed.  It's disappointing to see this
published by an otherwise excellent outfit like Wenzel.

The modifications make sense IMHO.  I suspect that the 2N3906's
are good for two reasons:  the low f-t reduces noise bandwidth
and the high current gain reduces noise current.

Rick Karlquist N6RK