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

[Gerhard Hoffmann]

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.


> 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! 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.


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.

---

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.


regards, Gerhard



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