On 11/07/2022 08:30, time-nuts-request@lists.febo.com wrote:

Indeed, those signal generators are renown for having "some rather
interesting" spectral content...
Around, above and often well below the "desired" signal!

Not entirely surprising though, if you look at the block diagram of one
such.

Regards to All.

Dave G0WBX(G8KBV)

--
Created on and sent from a Unix like PC running and using free and open source software:

yes there are much better signal generators out there, that frequency
doubler tuning circuit is for religious people only -- you need to be
able to believe, that it could work
73
KJ6UHN
Alex

On 7/11/2022 12:24 PM, Dave B via time-nuts wrote:

Hi

There are a very small number of signal generators that might
help when measuring phase noise on a good source. The “rest
of them” are very much in the “don’t bother” category. Just which
one is in the “maybe” category depends a lot on your frequency
of interest. None of them seem to be very affordable …. wonder
why :) :) :)

Do useful ones pop up from time to time? Sure they do. They might
require a bit of work to get going. Thanks very much to those who
make them available.

Bob

Hi

If you have any ceramic capacitors in the mix, they are often microphonic.
The X7R versions are typically the best “high C” types. NPO’s normally are
completely non-microphonic. Other non-ceramic caps should be ok, but
who knows.

Roughly speaking, 1 nV / Hz should be low enough to not matter. Since all
these specs are “typical” one never knows quite what this or that part may
be doing. You should see a drop putting in a 1 nV in place of a 5 nV.

Bob

On 7/12/22 8:53 AM, Erik Kaashoek via time-nuts wrote:

What's the noise contribution of the resistors? V = sqrt(4kTRB)

51 ohms  is sqrt (4 * 1.38E-23 * 300 * 51) = 0.9 nV/sqrt(Hz)  100 ohms
is ~1.4 nV/sqrt(Hz)

What kind of op amp? what's the current noise vs the voltage noise?  -
you might low voltage noise, but high current noise, and that current
noise across the input impedance can turn into surprisingly high voltage
noise at the output.

My guess would be a parasitic capacitance between circuit and housing.
changing the distance changes the C.

On Tue, 12 Jul 2022 08:17:33 -0800
Bob kb8tq via time-nuts time-nuts@lists.febo.com wrote:

Actually X7Rs are quite bad. Z5Us, also. Both are piezoelectric. I don't
use them any more except for power supply bypass in non-critical
supplies. As a part of a precision temperature controller project
(microKelvin), I needed to select capacitors for low microphonics.
The ceramic types mentioned above are the worst offenders; but
several other types (certain film types included) show some microphonic
activity.

Best to evaluate every capacitor type by charging to 10 Volts, or so, AC
coupling to an audio amplifier/sensitive oscilloscope/or other and tapping
to see if noise is produced.

Stephen Menasian

More excellent comments from Bob, this time about microphonic
capacitors.

It is interesting to note that the LT3042/LT3045 data sheets

recommend a Murata GJ831CR61E106KE83L ceramic capacitor because it is:

1. Low microphonic

and

2. Has a relatively small loss of capacitance due to DC voltage being
   applied

The amount of capacitance needed is prohibitively high to consider NPO.

This part is listed as "Not Recommended for New Design" at Digikey, but

they have over 24,000 in stock.  See URL:

https://www.eetimes.com/murata-low-profile-capacitors-reduce-acoustic-noise/#:~:text=Murata's%20GJ8%20series%20of%20multi,consumer%20and%20industrial%20electronics%20applications.

I see that on the Eval PCB's they use Samsung CL31A106MBHNNNE.  Digikey
has over 1 million of these in stock.

No info about how good they are.

--

Rick Karlquist
N6RK

On 2022-07-12 09:17, Bob kb8tq via time-nuts wrote:

generally the ceramic 'soft-termination' types are quiet. steer clear of
really Hi-k types like Y5V and Z5U.

anything other than CoG and NP0 are going to be like varactors, but that
wont matter so much IF you choose a nice high voltage. X7R are ok,
X5R....for PLLs if you choose something with heaps of voltage headroom.

If NPO gets too big, then I use solid tantalum capacitors in slow  PLLs,
(as the plastic MKT just get too big for my applications)....  but give
them heaps of voltage headroom - at least 3 x what the use voltage will
be....... they get much (current) noisier the higher the voltage on
them..  noise is in 10s of pA/root Hz. varies in mfr....

my 2c.

On 14/07/2022 9:16 am, Richard Karlquist via time-nuts wrote:

--
Glen English
RF Communications and Electronics Engineer

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