[mailto:time-nuts-boun...@febo.com] Im Auftrag von Bob Camp
Gesendet: Donnerstag, 11. September 2014 00:18
An: Discussion of precise time and frequency measurement
Betreff: Re: [time-nuts] OCXO Voltage Input? (Bob Camp)
Hi
If you are modulating a normal OCXO EFC with audio, and the output frequency
...@febo.com] Im Auftrag von Bob Camp
Gesendet: Donnerstag, 11. September 2014 00:18
An: Discussion of precise time and frequency measurement
Betreff: Re: [time-nuts] OCXO Voltage Input? (Bob Camp)
Hi
If you are modulating a normal OCXO EFC with audio, and the output frequency
is not being
: Donnerstag, 11. September 2014 00:18
An: Discussion of precise time and frequency measurement
Betreff: Re: [time-nuts] OCXO Voltage Input? (Bob Camp)
Hi
If you are modulating a normal OCXO EFC with audio, and the output
frequency is not being multiplied up, the modulation index will be very
, 7. September 2014 04:21
An: Discussion of precise time and frequency measurement
Betreff: Re: [time-nuts] OCXO Voltage Input? (Bob Camp)
Hi
Simple answer = crystals are never perfect.
Longer winded, but very incomplete answer =
A spurious response in a crystal normally refers to a mode
of precise time and frequency measurement
Betreff: Re: [time-nuts] OCXO Voltage Input? (Bob Camp)
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
www.axtal.com
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Von: time-nuts [mailto:time-nuts-boun...@febo.com] Im Auftrag von Bob Camp
Gesendet: Sonntag, 7. September 2014 04:21
An: Discussion of precise time and frequency measurement
Betreff: Re: [time-nuts] OCXO Voltage Input? (Bob Camp)
Hi
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
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
-fm-tuner-jitter-analysis.html
Subject: Re: [time-nuts] OCXO Voltage Input? (Bob Camp)
Message-ID: ccc8bc9e-c7af-4965-88c5-d3d21b41d...@n1k.org
Content-Type: text/plain; charset=windows-1252
Hi
Yes indeed, as you go below 1 Hz (or 1 radian/sec) all the things that “help”
you roll off wise now
frequency limit is in the 5-10 Hz range. The AFC of a good tuner will
eliminate most everything below that frequency.
More details here
http://www.diyaudio.com/forums/blogs/1audio/983-fm-tuner-jitter-analysis.html
Subject: Re: [time-nuts] OCXO Voltage Input? (Bob Camp)
Message-ID: ccc8bc9e-c7af
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 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
Hi Bob,
Being relatively new to this 'high end' time stuff, there's lots to
learn... So, how much bandwidth might a typical OCXO have on the EFC
pin? My assumption is that it is very low, but I have nothing to back
that up.
If I had 10Mhz or some other high frequency on the EFC line, would a
Some OCXO schematics:
http://leapsecond.com/museum/10544/
http://leapsecond.com/museum/10811a/
/tvb (i5s)
On Sep 5, 2014, at 5:50 AM, Dan Kemppainen d...@irtelemetrics.com wrote:
Hi Bob,
Being relatively new to this 'high end' time stuff, there's lots to
learn... So, how much bandwidth
Oh, while we are at it, how about the 10543?
Cheers,
Magnus
On 09/05/2014 03:49 PM, Tom Van Baak (lab) wrote:
Some OCXO schematics:
http://leapsecond.com/museum/10544/
http://leapsecond.com/museum/10811a/
/tvb (i5s)
On Sep 5, 2014, at 5:50 AM, Dan Kemppainen d...@irtelemetrics.com wrote:
Tom,
Awesome! Thanks!
Section 2-14. Since noise on the EFC line affects the oscillator's
stability (noise appears as FM on the output) care must be taken to
ensure that a relatively noise free EFC...
I was thinking the Varactor had be tied to the crystal, which only makes
sense. So, the bottom
no that is not so bad, there --inside of the box is always a small RC
which takes care the RF can't get into the oscillator, just look the
oscillator circuirs
73
Alex
On 9/5/2014 10:18 AM, Dan Kemppainen wrote:
Tom,
Awesome! Thanks!
Section 2-14. Since noise on the EFC line affects the
d...@irtelemetrics.com said:
If I had 10Mhz or some other high frequency on the EFC line, would a typical
OCXO respond to that?
Some VCXOs actually specify their bandwidth. High audio is sometimes useful.
I haven't seen anything beyond that, but I'm just listening to discussions
like this
The schematic provided shows two 20K resistors in series with the
varactor. So, yes there is some RC time constant. But is it enough to
filter our 100Hz or 1Khz, or 100Khz? I'll have to pull out the
calculator. The other issue, is I don't know how my OCXO is built. No
schematic.
Also, don't
it is not so easy to FM modulate a crystal oscillator, since the crystal
has a high Q therefore the modulation bandwidth of a crystal oscillator
is very narrow example: Q = F/dF - df = F/Q if F = 10MHz, Q = 60,000
dF = 166Hz
73
KJ6UHN
Alex
On 9/5/2014 1:10 PM, Hal Murray 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 pretty fast as you go up in modulation frequency.
Hi Bob
You have some good observations. Spread spectrum clocking is one I
hadn't considered when looking at this problem. In that case the
crystal is pulled a bunch. (It's also cheating in my opinion!)
Correcting for mechanical vibration in aircraft would also tend to
indicate it's
This topic comes up every few years.
I found an interesting thread back in late 2006.
Typical EFC frequency response (bandwidth) of a OCXO
https://www.febo.com/pipermail/time-nuts/2006-December/022758.html
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These are my opinions. I hate spam.
Hi all,
I have an PTI OCXO. The trimming voltage is two pins, with a maximum of
6.8VDC across the pins. They specify using a 20K pot as the adjustment
mechanism. However, I hope to use this thing in a closed loop, and will
be driving it with an active device.
What got me thinking is if the
Hi
The EFC pin *might* have a bypass cap on it. If you drive it with an op-amp an
isolating resistor might be needed. If so, a couple hundred ohms is likely
enough to stabilize the op-amp.
In a closed loop / control loop setting, the noise on the EFC will be whatever
the loop generates. As
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