[time-nuts] Odd-order multiplication of CMOS-output OCXO

[Bob kb8tq]

Hi

> On Jan 19, 2020, at 7:48 PM, Magnus Danielson <magnus at rubidium.se> wrote:
> 
> Hi Gerhard,
> 
> On 2020-01-20 00:03, Gerhard Hoffmann wrote:
>> 
>> Am 19.01.20 um 22:20 schrieb Magnus Danielson:
>>> Hi Mark,
>>> 
>>> On 2020-01-19 18:19, Mark Haun wrote:
>>> 
>>> I've read that I should avoid high-Q tuned circuits, because they
>>> will introduce more noise with temperature variation.  Are there
>>> any rules of thumb for how much Q is too much?
>> 
>> It's not that the high Q circuit generates noise, it's more
>> 
>> that the phase runs away when the resonant frequency runs away.
>> 
>> For a minimum phase network, you have +- 45° at the -3 dB points.
>> 
> Yes, the steep phase-slopes makes any shift cause great phase-shifts,
> which is another way of experiencing the group delay (= dphi/df), and
> the amplitude of that is proportional to the Q of a resonance. The phase
> is still 45 degrees at the -3 dB points, it's just that those is very close.

A very real question is — does this matter in the intended application? 

If the task at hand is measuring ADEV over 1,000 to 100,000 seconds, then yes indeed
it will come into play. If the task is demodulation audio with a lower cutoff of 10Hz
then no its not going to matter in the least little bit. The “noise” from a tuned 
circuit moving as the HVAC does it’s thing is *very* low frequency compared to
normal audio ….

Bob

>> 
>>> with a bit of scaling to give you jitter. Home-brewing this should not
>>> be too hard. Maybe it just lacks an example setup and some software
>>> support.
>> 
>> Ha, that hurts! Sheer mockery!
> No mockery intended.
>> I have spent the entire weekend
>> 
>> trying to control my 89441A FFT analyzer from Linux via a
>> 
>> Prologix USB-to-IEEE488 dongle. Setting /dev/ttyUSB0 to raw
>> 
>> and getting rid of the buffering was easy. Telling if that !#&%§!!
>> 
>> Prologix thing terminates the strings to the computer with LF
>> 
>> or CRLF seems impossible to predict, in spite of a command to
>> 
>> set this. And there is no way to measure anything on that virtual
>> 
>> tty port to watch the traffic. Use of tees activates buffering, no
>> 
>> way around.
>> 
>> Typical Heisenbug. Observing it affects the outcome.
> 
> I would be very interested to do exactly that. I've actually had issues
> getting the Prologix do things exactly as I want, and I blame that on my
> inability to focus long enough to read the manual to understand it
> properly. The lack of being able to debug the GPIB properly helps with
> the confusion. I need to do more GPIB programming, and perferably in
> Linux as I feel right at home there in general. One of my 89410s have
> cross-correlator capabilities, and I have a bit of other goodies, so it
> is about bringing things together.
> 
>> 
>> 
>> The idea was just to measure 1/f noise on my AF and RF transistors
>> 
>> in a circuit inspired by that in Art Of Electronics V3.
>> 
>> Good book. Must have.
> 
> That's not a bad starting-point if you only have that one book.
> 
> Now, which of the circuits did you get inspired from? I assume you where
> using one of the Chapter 8 circuits.
> 
>> 
>> ---
>> 
>> I have cut out the output amplifier circuit of my OCXO support
>> 
>> board and removed the doubler option and the notch filter. It provides
>> 
>> 22 dBm after a MV89A, enough for two ranks of power dividers in front
>> 
>> of the Timepod.  Transformers are still sub-optimum, esp. at the low end
>> 
>> and on the output side, but I wanted to avoid winding them myself.
>> 
>> DC emitter degeneration is 50 Ohm to fight 1/f, less than that above a
>> 
>> few 100 KHz as fits the gain. Push-pull common base.
>> 
>> 
>> A 10 MHz MV89A is internally 5 MHz, and you can see that in the spectrum.
>> 
>> External notch definitely required.
> 
> Ah, so they double rather than build a 5 and a 10 MHz core oscillator.
> There is some merits to that, and drawbacks.
> 
> I should have some of those lying around here somewhere.
> 
> Cheers,
> Magnus
> 
> 
> 
> 
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