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

[Magnus Danielson]

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.
>
>> 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