Bob,
On 09/06/2014 03:00 AM, Bob Camp wrote:
Hi
Oddly enough (and yes it is odd) you can modulate an oscillator well outside
the crystal’s bandwidth. The bigger issue is that the EFC does not pull the
crystal very far on a normal OCXO. The FM modulation index drops to very small
numbers
Hi
By far the most common way to check low level stuff on an OCXO is to measure
it’s phase noise. There are a variety of approaches. The lowest cost approach
is usually a dual oscillator into a mixer / quadrature lock. Feed the output to
a preamp and then into some sort of audio spectrum
Hi
Yes indeed, as you go below 1 Hz (or 1 radian/sec) all the things that “help”
you roll off wise now hurt you. If you are worried about sidebands inside 1 Hz,
you need to change a sign here and there. The only thing that saves you is that
the noise floor is now coming up pretty fast.
If
Yes, the source is at http://github.com/arodland/Due-GPS-NTP-Server .
It should be able to run just fine on the Due part of an Udoo, but
you'll have to come up with a different arrangement for the Ethernet.
One way would be to use chip-to-chip SPI to make the i.MX side of the
Udoo act
Will add it to my list of projects. Will touch bases when I get close.
Sent from my iPad
On Sep 6, 2014, at 10:18 AM, Andrew Rodland and...@cleverdomain.org wrote:
Yes, the source is at http://github.com/arodland/Due-GPS-NTP-Server .
It should be able to run just fine on the Due part of an
Hi Bob,
Agreed. I often find that modulations eats your margin out.
PWM is interesting in this regard. PWM has the property that the lowest
frequency has the highest amplitude and the overtones then decay with
1/f from that. For a given clock rate, as you add a bit of PWM
precision, you half
Hi
One of the easy things to do with PWM is to dither the LSB. That gives you one
more bit of precision. It still keeps the main tone at the same place.
Your worst case tone happens at 50% duty cycle (perfect square wave). If you do
your 50/50 as a square wave at Fmax(not Fmin), your
I have used an FM tuner pretty successfully to look at modulation and phase
noise in oscillators. For a 10 MHz oscillator you will be looking at the 10th
harmonic so modulation and phase noise is multiplied and much easier to see.
You do need a square wave output to get a lot of harmonics.
Hi
You get 20 log N multiplication in phase noise as you go up in frequency. On
the 10th harmonic you will be 20 db higher than on the fundamental. With an
OCXO running -160 to -170 dbc / Hz phase noise at the fundamental, you will be
at -140 to -150 dbc / Hz at 100 MHz. If you are at -155 dbc
Hi Bob,
Indeed. The way to keep the MCU PWM doing reasonable stuff is to use a
higher rate, and then update the PWM value in sync with the wrap-around,
and then alter the value (dither or whatever) so that the average has
higher precision. First degree sigma-delta is actually not a bad
Hi
If you are counting on your loop noise to spread your tones out - indeed not a
good idea. There are several ways you can “go quiet” in your loop….
Bob
On Sep 6, 2014, at 2:10 PM, Magnus Danielson mag...@rubidium.dyndns.org wrote:
Hi Bob,
Indeed. The way to keep the MCU PWM doing
Bob,
Agreed. I'm just saying that it goes static if you have PWM or something
similar.
As you see, there are many little details out there.
Cheers,
Magnus
On 09/06/2014 08:30 PM, Bob Camp wrote:
Hi
If you are counting on your loop noise to spread your tones out - indeed not a
good idea.
kb...@n1k.org said:
The biggest problem comes from crystal spurs rather than crystal Q.
What's the mechanism for making spurs with a crystal?
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On Fri, Sep 5, 2014 at 3:07 PM, Andrew Rodland and...@cleverdomain.org wrote:
1. Should I try using the analog EFC to zero out the amount of
correction I ask the X72's DDS for? Could reduce jitter in the
timebase, could just add noise. I suppose I can test this one easily
enough.
Update on
On Sat, Sep 6, 2014 at 9:13 PM, Hal Murray hmur...@megapathdsl.net wrote:
What's the mechanism for making spurs with a crystal?
Get the corners nice and pointy and strap it to a boot.
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Hi
Simple answer = crystals are never perfect.
Longer winded, but very incomplete answer =
A spurious response in a crystal normally refers to a mode that is not one of
the “identified” modes of the crystal. An AT has a set of identified modes, an
SC has a more complex set of modes. In the
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