S
skywatcher
Thu, Apr 19, 2012 7:10 PM
Hello @all,
my name is Wolfgang and i'm new to the list. :)
I browsed through the list archive, but i didn't find the infos i need,
so i decided to join the list
and to ask the experts directly. :)
I want to measure the frequency difference between a 10 MHz OCXO and a
10 MHz Rubidium.
I think that's what many people here have done many times... but i don't
want to use expensive
equipment like time interval counters with picosecond resolution etc. I
would prefer a cheap and
easy solution. I also would like to have an update rate of more than 1
measurement per second,
or even more.
My first approach was to use a simple XOR phase comparator. I tried a
74HCT86 and a 74HCT4046.
It works, but it's very noisy, so i don't get better than about 10 mHz
frequency resolution.
If i look at the lowpass-filtered output i don't see a nice sine or
triangular wave, but it looks more
than a triangular wave with round tops and some bumps between them.
Another problem is that the
difference frequency gets very low when the frequencies are very close,
so it's not enough to look
only for zero crossings of the difference signal.
Does anybody know a possibility to get a resolution < 1 mHz ?
Best regards,
Wolfgang
Hello @all,
my name is Wolfgang and i'm new to the list. :)
I browsed through the list archive, but i didn't find the infos i need,
so i decided to join the list
and to ask the experts directly. :)
I want to measure the frequency difference between a 10 MHz OCXO and a
10 MHz Rubidium.
I think that's what many people here have done many times... but i don't
want to use expensive
equipment like time interval counters with picosecond resolution etc. I
would prefer a cheap and
easy solution. I also would like to have an update rate of more than 1
measurement per second,
or even more.
My first approach was to use a simple XOR phase comparator. I tried a
74HCT86 and a 74HCT4046.
It works, but it's very noisy, so i don't get better than about 10 mHz
frequency resolution.
If i look at the lowpass-filtered output i don't see a nice sine or
triangular wave, but it looks more
than a triangular wave with round tops and some bumps between them.
Another problem is that the
difference frequency gets very low when the frequencies are very close,
so it's not enough to look
only for zero crossings of the difference signal.
Does anybody know a possibility to get a resolution < 1 mHz ?
Best regards,
Wolfgang
L
lists@lazygranch.com
Thu, Apr 19, 2012 7:23 PM
Just a speculation on my part, but if you got some non-saturating logic like ECL, the jitter would be less.
I haven't done any ECL in years, but the traces I got from ECL circuits are amazingly clean. I was evaluating a competitions ECL DAC.
-----Original Message-----
From: skywatcher skywatcher@web.de
Sender: time-nuts-bounces@febo.com
Date: Thu, 19 Apr 2012 21:10:03
To: time-nuts@febo.com
Reply-To: Discussion of precise time and frequency measurement
time-nuts@febo.com
Subject: [time-nuts] Question about precise frequency / phase measurement
Hello @all,
my name is Wolfgang and i'm new to the list. :)
I browsed through the list archive, but i didn't find the infos i need,
so i decided to join the list
and to ask the experts directly. :)
I want to measure the frequency difference between a 10 MHz OCXO and a
10 MHz Rubidium.
I think that's what many people here have done many times... but i don't
want to use expensive
equipment like time interval counters with picosecond resolution etc. I
would prefer a cheap and
easy solution. I also would like to have an update rate of more than 1
measurement per second,
or even more.
My first approach was to use a simple XOR phase comparator. I tried a
74HCT86 and a 74HCT4046.
It works, but it's very noisy, so i don't get better than about 10 mHz
frequency resolution.
If i look at the lowpass-filtered output i don't see a nice sine or
triangular wave, but it looks more
than a triangular wave with round tops and some bumps between them.
Another problem is that the
difference frequency gets very low when the frequencies are very close,
so it's not enough to look
only for zero crossings of the difference signal.
Does anybody know a possibility to get a resolution < 1 mHz ?
Best regards,
Wolfgang
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
Just a speculation on my part, but if you got some non-saturating logic like ECL, the jitter would be less.
I haven't done any ECL in years, but the traces I got from ECL circuits are amazingly clean. I was evaluating a competitions ECL DAC.
-----Original Message-----
From: skywatcher <skywatcher@web.de>
Sender: time-nuts-bounces@febo.com
Date: Thu, 19 Apr 2012 21:10:03
To: <time-nuts@febo.com>
Reply-To: Discussion of precise time and frequency measurement
<time-nuts@febo.com>
Subject: [time-nuts] Question about precise frequency / phase measurement
Hello @all,
my name is Wolfgang and i'm new to the list. :)
I browsed through the list archive, but i didn't find the infos i need,
so i decided to join the list
and to ask the experts directly. :)
I want to measure the frequency difference between a 10 MHz OCXO and a
10 MHz Rubidium.
I think that's what many people here have done many times... but i don't
want to use expensive
equipment like time interval counters with picosecond resolution etc. I
would prefer a cheap and
easy solution. I also would like to have an update rate of more than 1
measurement per second,
or even more.
My first approach was to use a simple XOR phase comparator. I tried a
74HCT86 and a 74HCT4046.
It works, but it's very noisy, so i don't get better than about 10 mHz
frequency resolution.
If i look at the lowpass-filtered output i don't see a nice sine or
triangular wave, but it looks more
than a triangular wave with round tops and some bumps between them.
Another problem is that the
difference frequency gets very low when the frequencies are very close,
so it's not enough to look
only for zero crossings of the difference signal.
Does anybody know a possibility to get a resolution < 1 mHz ?
Best regards,
Wolfgang
_______________________________________________
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
JF
J. Forster
Thu, Apr 19, 2012 7:24 PM
Hello @all,
my name is Wolfgang and i'm new to the list. :)
I browsed through the list archive, but i didn't find the infos i need,
so i decided to join the list
and to ask the experts directly. :)
I want to measure the frequency difference between a 10 MHz OCXO and a
10 MHz Rubidium.
I think that's what many people here have done many times... but i don't
want to use expensive
equipment like time interval counters with picosecond resolution etc. I
would prefer a cheap and
easy solution. I also would like to have an update rate of more than 1
measurement per second,
or even more.
My first approach was to use a simple XOR phase comparator. I tried a
74HCT86 and a 74HCT4046.
It works, but it's very noisy, so i don't get better than about 10 mHz
frequency resolution.
If i look at the lowpass-filtered output i don't see a nice sine or
triangular wave, but it looks more
than a triangular wave with round tops and some bumps between them.
You would only see a sine wave if the difference frequency was stable an
such that the LPF cut off all but the fundamental.
If you want sine wave output, use an analog mixer on sine waves, and don't
overdrive it.
-John
===============
Another problem is that the
difference frequency gets very low when the frequencies are very close,
so it's not enough to look
only for zero crossings of the difference signal.
Does anybody know a possibility to get a resolution < 1 mHz ?
Best regards,
Wolfgang
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
Welcome,
> Hello @all,
>
> my name is Wolfgang and i'm new to the list. :)
>
> I browsed through the list archive, but i didn't find the infos i need,
> so i decided to join the list
> and to ask the experts directly. :)
>
> I want to measure the frequency difference between a 10 MHz OCXO and a
> 10 MHz Rubidium.
> I think that's what many people here have done many times... but i don't
> want to use expensive
> equipment like time interval counters with picosecond resolution etc. I
> would prefer a cheap and
> easy solution. I also would like to have an update rate of more than 1
> measurement per second,
> or even more.
>
> My first approach was to use a simple XOR phase comparator. I tried a
> 74HCT86 and a 74HCT4046.
> It works, but it's very noisy, so i don't get better than about 10 mHz
> frequency resolution.
> If i look at the lowpass-filtered output i don't see a nice sine or
> triangular wave, but it looks more
> than a triangular wave with round tops and some bumps between them.
You would only see a sine wave if the difference frequency was stable an
such that the LPF cut off all but the fundamental.
If you want sine wave output, use an analog mixer on sine waves, and don't
overdrive it.
-John
===============
> Another problem is that the
> difference frequency gets very low when the frequencies are very close,
> so it's not enough to look
> only for zero crossings of the difference signal.
>
> Does anybody know a possibility to get a resolution < 1 mHz ?
>
> Best regards,
> Wolfgang
>
>
> _______________________________________________
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>
>
MD
Magnus Danielson
Thu, Apr 19, 2012 7:31 PM
Hi Wolfgang,
On 19/04/12 21:10, skywatcher wrote:
Hello @all,
my name is Wolfgang and i'm new to the list. :)
I want to measure the frequency difference between a 10 MHz OCXO and a
10 MHz Rubidium.
I think that's what many people here have done many times... but i don't
want to use expensive
equipment like time interval counters with picosecond resolution etc. I
would prefer a cheap and
easy solution. I also would like to have an update rate of more than 1
measurement per second,
or even more.
My first approach was to use a simple XOR phase comparator. I tried a
74HCT86 and a 74HCT4046.
It works, but it's very noisy, so i don't get better than about 10 mHz
frequency resolution.
If i look at the lowpass-filtered output i don't see a nice sine or
triangular wave, but it looks more
than a triangular wave with round tops and some bumps between them.
Another problem is that the
difference frequency gets very low when the frequencies are very close,
so it's not enough to look
only for zero crossings of the difference signal.
Does anybody know a possibility to get a resolution < 1 mHz ?
Have you looked at the PICTIC II project? It's not too bad.
There is several other possible projects to consider, but the PICTIC II
may be a good start. Also look at a divide down system such as the TADD
2 divider or the just released TADD 2 Mini.
There is a challenge in doing fairly high precission for low budget here
on the list. Besides measuring frequency, we pride ourselves in
measuring the frequency stability, Allan Deviation (ADEV), as good as
possible.
Cheers,
Magnus
Hi Wolfgang,
On 19/04/12 21:10, skywatcher wrote:
> Hello @all,
>
> my name is Wolfgang and i'm new to the list. :)
Welcome!
> I want to measure the frequency difference between a 10 MHz OCXO and a
> 10 MHz Rubidium.
> I think that's what many people here have done many times... but i don't
> want to use expensive
> equipment like time interval counters with picosecond resolution etc. I
> would prefer a cheap and
> easy solution. I also would like to have an update rate of more than 1
> measurement per second,
> or even more.
>
> My first approach was to use a simple XOR phase comparator. I tried a
> 74HCT86 and a 74HCT4046.
> It works, but it's very noisy, so i don't get better than about 10 mHz
> frequency resolution.
> If i look at the lowpass-filtered output i don't see a nice sine or
> triangular wave, but it looks more
> than a triangular wave with round tops and some bumps between them.
> Another problem is that the
> difference frequency gets very low when the frequencies are very close,
> so it's not enough to look
> only for zero crossings of the difference signal.
>
> Does anybody know a possibility to get a resolution < 1 mHz ?
Have you looked at the PICTIC II project? It's not too bad.
There is several other possible projects to consider, but the PICTIC II
may be a good start. Also look at a divide down system such as the TADD
2 divider or the just released TADD 2 Mini.
There is a challenge in doing fairly high precission for low budget here
on the list. Besides measuring frequency, we pride ourselves in
measuring the frequency stability, Allan Deviation (ADEV), as good as
possible.
Cheers,
Magnus
AB
Azelio Boriani
Thu, Apr 19, 2012 7:37 PM
And, if you are measuring, by analog mixing, two very slightly different
frequencies, what do you expect to obtain if not a signal that is slow,
very slow. How can you measure milliHertz or microHertz without waiting?
On Thu, Apr 19, 2012 at 9:31 PM, Magnus Danielson <
magnus@rubidium.dyndns.org> wrote:
Hi Wolfgang,
On 19/04/12 21:10, skywatcher wrote:
Hello @all,
my name is Wolfgang and i'm new to the list. :)
Welcome!
I want to measure the frequency difference between a 10 MHz OCXO and a
10 MHz Rubidium.
I think that's what many people here have done many times... but i don't
want to use expensive
equipment like time interval counters with picosecond resolution etc. I
would prefer a cheap and
easy solution. I also would like to have an update rate of more than 1
measurement per second,
or even more.
My first approach was to use a simple XOR phase comparator. I tried a
74HCT86 and a 74HCT4046.
It works, but it's very noisy, so i don't get better than about 10 mHz
frequency resolution.
If i look at the lowpass-filtered output i don't see a nice sine or
triangular wave, but it looks more
than a triangular wave with round tops and some bumps between them.
Another problem is that the
difference frequency gets very low when the frequencies are very close,
so it's not enough to look
only for zero crossings of the difference signal.
Does anybody know a possibility to get a resolution < 1 mHz ?
Have you looked at the PICTIC II project? It's not too bad.
There is several other possible projects to consider, but the PICTIC II
may be a good start. Also look at a divide down system such as the TADD 2
divider or the just released TADD 2 Mini.
There is a challenge in doing fairly high precission for low budget here
on the list. Besides measuring frequency, we pride ourselves in measuring
the frequency stability, Allan Deviation (ADEV), as good as possible.
Cheers,
Magnus
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
And, if you are measuring, by analog mixing, two very slightly different
frequencies, what do you expect to obtain if not a signal that is slow,
very slow. How can you measure milliHertz or microHertz without waiting?
On Thu, Apr 19, 2012 at 9:31 PM, Magnus Danielson <
magnus@rubidium.dyndns.org> wrote:
> Hi Wolfgang,
>
>
> On 19/04/12 21:10, skywatcher wrote:
>
>> Hello @all,
>>
>> my name is Wolfgang and i'm new to the list. :)
>>
>
> Welcome!
>
>
> I want to measure the frequency difference between a 10 MHz OCXO and a
>> 10 MHz Rubidium.
>> I think that's what many people here have done many times... but i don't
>> want to use expensive
>> equipment like time interval counters with picosecond resolution etc. I
>> would prefer a cheap and
>> easy solution. I also would like to have an update rate of more than 1
>> measurement per second,
>> or even more.
>>
>> My first approach was to use a simple XOR phase comparator. I tried a
>> 74HCT86 and a 74HCT4046.
>> It works, but it's very noisy, so i don't get better than about 10 mHz
>> frequency resolution.
>> If i look at the lowpass-filtered output i don't see a nice sine or
>> triangular wave, but it looks more
>> than a triangular wave with round tops and some bumps between them.
>> Another problem is that the
>> difference frequency gets very low when the frequencies are very close,
>> so it's not enough to look
>> only for zero crossings of the difference signal.
>>
>> Does anybody know a possibility to get a resolution < 1 mHz ?
>>
>
> Have you looked at the PICTIC II project? It's not too bad.
>
> There is several other possible projects to consider, but the PICTIC II
> may be a good start. Also look at a divide down system such as the TADD 2
> divider or the just released TADD 2 Mini.
>
> There is a challenge in doing fairly high precission for low budget here
> on the list. Besides measuring frequency, we pride ourselves in measuring
> the frequency stability, Allan Deviation (ADEV), as good as possible.
>
> Cheers,
> Magnus
>
>
> _______________________________________________
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>
BG
Bruce Griffiths
Thu, Apr 19, 2012 7:51 PM
Using a dual mixer time difference system (either the digital dual mixer
time difference (DDMTD) or the analog variant (DMTD)) can easily achieve
the required resolution.
The DDMTD is relatively cheap to implement however it requires an offset
oscillator to beat against the 2 signals being compared.
However a DDMTD can use a 5MHz offset oscillator can be used with 5MHz,
10MHz, 15MHz ... input signals whereas a DMTD requires a 10MHz offset
oscillator to be used with 10Mhz input signals.
The DDMTD uses a pair of shift registers clocked by the offset source
where each of the 2 signals being compared is connected to the data
inputs of its shift register.
The time difference between beat outputs of the 2 shift registers is
then measured with relatively low resolution.
Some digital filtering of the shift register output transitions is
usually required.
A pair of 74HC164's will typically have a equivalent input jitter of
around 10ps or so, a 74AC164 will be about 4x quieter.
With a 5.000055MHz offset oscillator and 10MHz inputs the shift register
output beat frequency will be 110Hz.
It is usually advantageous to use an FPGA to implement the digital
filtering, timestamping and even the shift registers (although external
shift registers will have less crosstalk).
Bruce
skywatcher wrote:
Hello @all,
my name is Wolfgang and i'm new to the list. :)
I browsed through the list archive, but i didn't find the infos i
need, so i decided to join the list
and to ask the experts directly. :)
I want to measure the frequency difference between a 10 MHz OCXO and a
10 MHz Rubidium.
I think that's what many people here have done many times... but i
don't want to use expensive
equipment like time interval counters with picosecond resolution etc.
I would prefer a cheap and
easy solution. I also would like to have an update rate of more than 1
measurement per second,
or even more.
My first approach was to use a simple XOR phase comparator. I tried a
74HCT86 and a 74HCT4046.
It works, but it's very noisy, so i don't get better than about 10 mHz
frequency resolution.
If i look at the lowpass-filtered output i don't see a nice sine or
triangular wave, but it looks more
than a triangular wave with round tops and some bumps between them.
Another problem is that the
difference frequency gets very low when the frequencies are very
close, so it's not enough to look
only for zero crossings of the difference signal.
Does anybody know a possibility to get a resolution < 1 mHz ?
Best regards,
Wolfgang
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
Using a dual mixer time difference system (either the digital dual mixer
time difference (DDMTD) or the analog variant (DMTD)) can easily achieve
the required resolution.
The DDMTD is relatively cheap to implement however it requires an offset
oscillator to beat against the 2 signals being compared.
However a DDMTD can use a 5MHz offset oscillator can be used with 5MHz,
10MHz, 15MHz ... input signals whereas a DMTD requires a 10MHz offset
oscillator to be used with 10Mhz input signals.
The DDMTD uses a pair of shift registers clocked by the offset source
where each of the 2 signals being compared is connected to the data
inputs of its shift register.
The time difference between beat outputs of the 2 shift registers is
then measured with relatively low resolution.
Some digital filtering of the shift register output transitions is
usually required.
A pair of 74HC164's will typically have a equivalent input jitter of
around 10ps or so, a 74AC164 will be about 4x quieter.
With a 5.000055MHz offset oscillator and 10MHz inputs the shift register
output beat frequency will be 110Hz.
It is usually advantageous to use an FPGA to implement the digital
filtering, timestamping and even the shift registers (although external
shift registers will have less crosstalk).
Bruce
skywatcher wrote:
> Hello @all,
>
> my name is Wolfgang and i'm new to the list. :)
>
> I browsed through the list archive, but i didn't find the infos i
> need, so i decided to join the list
> and to ask the experts directly. :)
>
> I want to measure the frequency difference between a 10 MHz OCXO and a
> 10 MHz Rubidium.
> I think that's what many people here have done many times... but i
> don't want to use expensive
> equipment like time interval counters with picosecond resolution etc.
> I would prefer a cheap and
> easy solution. I also would like to have an update rate of more than 1
> measurement per second,
> or even more.
>
> My first approach was to use a simple XOR phase comparator. I tried a
> 74HCT86 and a 74HCT4046.
> It works, but it's very noisy, so i don't get better than about 10 mHz
> frequency resolution.
> If i look at the lowpass-filtered output i don't see a nice sine or
> triangular wave, but it looks more
> than a triangular wave with round tops and some bumps between them.
> Another problem is that the
> difference frequency gets very low when the frequencies are very
> close, so it's not enough to look
> only for zero crossings of the difference signal.
>
> Does anybody know a possibility to get a resolution < 1 mHz ?
>
> Best regards,
> Wolfgang
>
>
> _______________________________________________
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>
BG
Bruce Griffiths
Thu, Apr 19, 2012 7:53 PM
Use a dual mixer system with an offset LO.
Bruce
Azelio Boriani wrote:
And, if you are measuring, by analog mixing, two very slightly different
frequencies, what do you expect to obtain if not a signal that is slow,
very slow. How can you measure milliHertz or microHertz without waiting?
On Thu, Apr 19, 2012 at 9:31 PM, Magnus Danielson<
magnus@rubidium.dyndns.org> wrote:
Hi Wolfgang,
On 19/04/12 21:10, skywatcher wrote:
Hello @all,
my name is Wolfgang and i'm new to the list. :)
Welcome!
I want to measure the frequency difference between a 10 MHz OCXO and a
10 MHz Rubidium.
I think that's what many people here have done many times... but i don't
want to use expensive
equipment like time interval counters with picosecond resolution etc. I
would prefer a cheap and
easy solution. I also would like to have an update rate of more than 1
measurement per second,
or even more.
My first approach was to use a simple XOR phase comparator. I tried a
74HCT86 and a 74HCT4046.
It works, but it's very noisy, so i don't get better than about 10 mHz
frequency resolution.
If i look at the lowpass-filtered output i don't see a nice sine or
triangular wave, but it looks more
than a triangular wave with round tops and some bumps between them.
Another problem is that the
difference frequency gets very low when the frequencies are very close,
so it's not enough to look
only for zero crossings of the difference signal.
Does anybody know a possibility to get a resolution< 1 mHz ?
Have you looked at the PICTIC II project? It's not too bad.
There is several other possible projects to consider, but the PICTIC II
may be a good start. Also look at a divide down system such as the TADD 2
divider or the just released TADD 2 Mini.
There is a challenge in doing fairly high precission for low budget here
on the list. Besides measuring frequency, we pride ourselves in measuring
the frequency stability, Allan Deviation (ADEV), as good as possible.
Cheers,
Magnus
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
Use a dual mixer system with an offset LO.
Bruce
Azelio Boriani wrote:
> And, if you are measuring, by analog mixing, two very slightly different
> frequencies, what do you expect to obtain if not a signal that is slow,
> very slow. How can you measure milliHertz or microHertz without waiting?
>
> On Thu, Apr 19, 2012 at 9:31 PM, Magnus Danielson<
> magnus@rubidium.dyndns.org> wrote:
>
>
>> Hi Wolfgang,
>>
>>
>> On 19/04/12 21:10, skywatcher wrote:
>>
>>
>>> Hello @all,
>>>
>>> my name is Wolfgang and i'm new to the list. :)
>>>
>>>
>> Welcome!
>>
>>
>> I want to measure the frequency difference between a 10 MHz OCXO and a
>>
>>> 10 MHz Rubidium.
>>> I think that's what many people here have done many times... but i don't
>>> want to use expensive
>>> equipment like time interval counters with picosecond resolution etc. I
>>> would prefer a cheap and
>>> easy solution. I also would like to have an update rate of more than 1
>>> measurement per second,
>>> or even more.
>>>
>>> My first approach was to use a simple XOR phase comparator. I tried a
>>> 74HCT86 and a 74HCT4046.
>>> It works, but it's very noisy, so i don't get better than about 10 mHz
>>> frequency resolution.
>>> If i look at the lowpass-filtered output i don't see a nice sine or
>>> triangular wave, but it looks more
>>> than a triangular wave with round tops and some bumps between them.
>>> Another problem is that the
>>> difference frequency gets very low when the frequencies are very close,
>>> so it's not enough to look
>>> only for zero crossings of the difference signal.
>>>
>>> Does anybody know a possibility to get a resolution< 1 mHz ?
>>>
>>>
>> Have you looked at the PICTIC II project? It's not too bad.
>>
>> There is several other possible projects to consider, but the PICTIC II
>> may be a good start. Also look at a divide down system such as the TADD 2
>> divider or the just released TADD 2 Mini.
>>
>> There is a challenge in doing fairly high precission for low budget here
>> on the list. Besides measuring frequency, we pride ourselves in measuring
>> the frequency stability, Allan Deviation (ADEV), as good as possible.
>>
>> Cheers,
>> Magnus
>>
>>
>> _______________________________________________
>> time-nuts mailing list -- time-nuts@febo.com
>> To unsubscribe, go to
>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>>
>>
> _______________________________________________
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>
>
AB
Azelio Boriani
Thu, Apr 19, 2012 7:55 PM
Of course, there are PICTIC II, DMTD, DDMTD, SR620, HP5370B, Wavecrest,
PM6681, HP53132. The simplest is using a scope and... wait.
On Thu, Apr 19, 2012 at 9:53 PM, Bruce Griffiths <bruce.griffiths@xtra.co.nz
Use a dual mixer system with an offset LO.
Bruce
Azelio Boriani wrote:
And, if you are measuring, by analog mixing, two very slightly different
frequencies, what do you expect to obtain if not a signal that is slow,
very slow. How can you measure milliHertz or microHertz without waiting?
On Thu, Apr 19, 2012 at 9:31 PM, Magnus Danielson<
magnus@rubidium.dyndns.org> wrote:
Hi Wolfgang,
On 19/04/12 21:10, skywatcher wrote:
Hello @all,
my name is Wolfgang and i'm new to the list. :)
Welcome!
I want to measure the frequency difference between a 10 MHz OCXO and a
10 MHz Rubidium.
I think that's what many people here have done many times... but i don't
want to use expensive
equipment like time interval counters with picosecond resolution etc. I
would prefer a cheap and
easy solution. I also would like to have an update rate of more than 1
measurement per second,
or even more.
My first approach was to use a simple XOR phase comparator. I tried a
74HCT86 and a 74HCT4046.
It works, but it's very noisy, so i don't get better than about 10 mHz
frequency resolution.
If i look at the lowpass-filtered output i don't see a nice sine or
triangular wave, but it looks more
than a triangular wave with round tops and some bumps between them.
Another problem is that the
difference frequency gets very low when the frequencies are very close,
so it's not enough to look
only for zero crossings of the difference signal.
Does anybody know a possibility to get a resolution< 1 mHz ?
Have you looked at the PICTIC II project? It's not too bad.
There is several other possible projects to consider, but the PICTIC II
may be a good start. Also look at a divide down system such as the TADD 2
divider or the just released TADD 2 Mini.
There is a challenge in doing fairly high precission for low budget here
on the list. Besides measuring frequency, we pride ourselves in measuring
the frequency stability, Allan Deviation (ADEV), as good as possible.
Cheers,
Magnus
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Of course, there are PICTIC II, DMTD, DDMTD, SR620, HP5370B, Wavecrest,
PM6681, HP53132. The simplest is using a scope and... wait.
On Thu, Apr 19, 2012 at 9:53 PM, Bruce Griffiths <bruce.griffiths@xtra.co.nz
> wrote:
> Use a dual mixer system with an offset LO.
>
> Bruce
>
> Azelio Boriani wrote:
>
>> And, if you are measuring, by analog mixing, two very slightly different
>> frequencies, what do you expect to obtain if not a signal that is slow,
>> very slow. How can you measure milliHertz or microHertz without waiting?
>>
>> On Thu, Apr 19, 2012 at 9:31 PM, Magnus Danielson<
>> magnus@rubidium.dyndns.org> wrote:
>>
>>
>>
>>> Hi Wolfgang,
>>>
>>>
>>>
>>> On 19/04/12 21:10, skywatcher wrote:
>>>
>>>
>>>
>>>> Hello @all,
>>>>
>>>> my name is Wolfgang and i'm new to the list. :)
>>>>
>>>>
>>>>
>>> Welcome!
>>>
>>>
>>>
>>> I want to measure the frequency difference between a 10 MHz OCXO and a
>>>
>>>
>>>> 10 MHz Rubidium.
>>>> I think that's what many people here have done many times... but i don't
>>>> want to use expensive
>>>> equipment like time interval counters with picosecond resolution etc. I
>>>> would prefer a cheap and
>>>> easy solution. I also would like to have an update rate of more than 1
>>>> measurement per second,
>>>> or even more.
>>>>
>>>> My first approach was to use a simple XOR phase comparator. I tried a
>>>> 74HCT86 and a 74HCT4046.
>>>> It works, but it's very noisy, so i don't get better than about 10 mHz
>>>> frequency resolution.
>>>> If i look at the lowpass-filtered output i don't see a nice sine or
>>>> triangular wave, but it looks more
>>>> than a triangular wave with round tops and some bumps between them.
>>>> Another problem is that the
>>>> difference frequency gets very low when the frequencies are very close,
>>>> so it's not enough to look
>>>> only for zero crossings of the difference signal.
>>>>
>>>> Does anybody know a possibility to get a resolution< 1 mHz ?
>>>>
>>>>
>>>>
>>> Have you looked at the PICTIC II project? It's not too bad.
>>>
>>> There is several other possible projects to consider, but the PICTIC II
>>> may be a good start. Also look at a divide down system such as the TADD 2
>>> divider or the just released TADD 2 Mini.
>>>
>>> There is a challenge in doing fairly high precission for low budget here
>>> on the list. Besides measuring frequency, we pride ourselves in measuring
>>> the frequency stability, Allan Deviation (ADEV), as good as possible.
>>>
>>> Cheers,
>>> Magnus
>>>
>>>
>>>
>>> _______________________________________________
>>> time-nuts mailing list -- time-nuts@febo.com
>>> To unsubscribe, go to
>>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>>> and follow the instructions there.
>>>
>>>
>>>
>> _______________________________________________
>> time-nuts mailing list -- time-nuts@febo.com
>> To unsubscribe, go to
>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>>
>>
>>
>
>
> _______________________________________________
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>
S
skywatcher
Thu, Apr 19, 2012 8:02 PM
Hi Bruce,
this sounds very good, and seems to fit my requirements quite well. :)
I will have a closer look to this concept.
I also had the idea to take the reference frequency, divide it, and mix
the division result again with the reference
to get an offset to the reference frequency which would give a higher
beat frequency which allows a reasonable measurement rate.
But it didn't turn out as i expected, because there was a lot of
'garbage' in the signals.
Best regards,
Wolfgang
Am 19.04.2012 21:51, schrieb Bruce Griffiths:
Using a dual mixer time difference system (either the digital dual
mixer time difference (DDMTD) or the analog variant (DMTD)) can easily
achieve the required resolution.
The DDMTD is relatively cheap to implement however it requires an
offset oscillator to beat against the 2 signals being compared.
However a DDMTD can use a 5MHz offset oscillator can be used with
5MHz, 10MHz, 15MHz ... input signals whereas a DMTD requires a 10MHz
offset oscillator to be used with 10Mhz input signals.
The DDMTD uses a pair of shift registers clocked by the offset source
where each of the 2 signals being compared is connected to the data
inputs of its shift register.
The time difference between beat outputs of the 2 shift registers is
then measured with relatively low resolution.
Some digital filtering of the shift register output transitions is
usually required.
A pair of 74HC164's will typically have a equivalent input jitter of
around 10ps or so, a 74AC164 will be about 4x quieter.
With a 5.000055MHz offset oscillator and 10MHz inputs the shift
register output beat frequency will be 110Hz.
It is usually advantageous to use an FPGA to implement the digital
filtering, timestamping and even the shift registers (although
external shift registers will have less crosstalk).
Bruce
Hi Bruce,
this sounds very good, and seems to fit my requirements quite well. :)
I will have a closer look to this concept.
I also had the idea to take the reference frequency, divide it, and mix
the division result again with the reference
to get an offset to the reference frequency which would give a higher
beat frequency which allows a reasonable measurement rate.
But it didn't turn out as i expected, because there was a lot of
'garbage' in the signals.
Best regards,
Wolfgang
Am 19.04.2012 21:51, schrieb Bruce Griffiths:
> Using a dual mixer time difference system (either the digital dual
> mixer time difference (DDMTD) or the analog variant (DMTD)) can easily
> achieve the required resolution.
> The DDMTD is relatively cheap to implement however it requires an
> offset oscillator to beat against the 2 signals being compared.
> However a DDMTD can use a 5MHz offset oscillator can be used with
> 5MHz, 10MHz, 15MHz ... input signals whereas a DMTD requires a 10MHz
> offset oscillator to be used with 10Mhz input signals.
>
> The DDMTD uses a pair of shift registers clocked by the offset source
> where each of the 2 signals being compared is connected to the data
> inputs of its shift register.
> The time difference between beat outputs of the 2 shift registers is
> then measured with relatively low resolution.
> Some digital filtering of the shift register output transitions is
> usually required.
> A pair of 74HC164's will typically have a equivalent input jitter of
> around 10ps or so, a 74AC164 will be about 4x quieter.
>
> With a 5.000055MHz offset oscillator and 10MHz inputs the shift
> register output beat frequency will be 110Hz.
>
> It is usually advantageous to use an FPGA to implement the digital
> filtering, timestamping and even the shift registers (although
> external shift registers will have less crosstalk).
>
> Bruce
JM
Joseph M Gwinn
Thu, Apr 19, 2012 10:14 PM
The traditional approach was to use a double-balanced mixer configured as a
phase detector, pass the phase detector output through a low-pass filter
(with 1 Hz bandwidth), and plot the result using a chart recorder. The
chart recorder would also have marks from some kind of accurate clock.
After a few days of recording, the beat frequency is easily determined, as
is variations over the day. The present-day equivalent replaces the chart
recorder with a recording digital voltmeter of some kind.
Joe Gwinn
From: Azelio Boriani azelio.boriani@screen.it
To: Discussion of precise time and frequency measurement
time-nuts@febo.com
Date: 04/19/2012 03:38 PM
Subject: Re: [time-nuts] Question about precise frequency / phase
measurement
Sent by: time-nuts-bounces@febo.com
And, if you are measuring, by analog mixing, two very slightly different
frequencies, what do you expect to obtain if not a signal that is slow,
very slow. How can you measure milliHertz or microHertz without waiting?
On Thu, Apr 19, 2012 at 9:31 PM, Magnus Danielson <
magnus@rubidium.dyndns.org> wrote:
Hi Wolfgang,
On 19/04/12 21:10, skywatcher wrote:
Hello @all,
my name is Wolfgang and i'm new to the list. :)
Welcome!
I want to measure the frequency difference between a 10 MHz OCXO and a
10 MHz Rubidium.
I think that's what many people here have done many times... but i don't
want to use expensive
equipment like time interval counters with picosecond resolution etc. I
would prefer a cheap and
easy solution. I also would like to have an update rate of more than 1
measurement per second,
or even more.
My first approach was to use a simple XOR phase comparator. I tried a
74HCT86 and a 74HCT4046.
It works, but it's very noisy, so i don't get better than about 10 mHz
frequency resolution.
If i look at the lowpass-filtered output i don't see a nice sine or
triangular wave, but it looks more
than a triangular wave with round tops and some bumps between them.
Another problem is that the
difference frequency gets very low when the frequencies are very close,
so it's not enough to look
only for zero crossings of the difference signal.
Does anybody know a possibility to get a resolution < 1 mHz ?
Have you looked at the PICTIC II project? It's not too bad.
There is several other possible projects to consider, but the PICTIC II
may be a good start. Also look at a divide down system such as the TADD 2
divider or the just released TADD 2 Mini.
There is a challenge in doing fairly high precission for low budget here
on the list. Besides measuring frequency, we pride ourselves in measuring
the frequency stability, Allan Deviation (ADEV), as good as possible.
Cheers,
Magnus
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
The traditional approach was to use a double-balanced mixer configured as a
phase detector, pass the phase detector output through a low-pass filter
(with 1 Hz bandwidth), and plot the result using a chart recorder. The
chart recorder would also have marks from some kind of accurate clock.
After a few days of recording, the beat frequency is easily determined, as
is variations over the day. The present-day equivalent replaces the chart
recorder with a recording digital voltmeter of some kind.
Joe Gwinn
From: Azelio Boriani <azelio.boriani@screen.it>
To: Discussion of precise time and frequency measurement
<time-nuts@febo.com>
Date: 04/19/2012 03:38 PM
Subject: Re: [time-nuts] Question about precise frequency / phase
measurement
Sent by: time-nuts-bounces@febo.com
And, if you are measuring, by analog mixing, two very slightly different
frequencies, what do you expect to obtain if not a signal that is slow,
very slow. How can you measure milliHertz or microHertz without waiting?
On Thu, Apr 19, 2012 at 9:31 PM, Magnus Danielson <
magnus@rubidium.dyndns.org> wrote:
> Hi Wolfgang,
>
>
> On 19/04/12 21:10, skywatcher wrote:
>
>> Hello @all,
>>
>> my name is Wolfgang and i'm new to the list. :)
>>
>
> Welcome!
>
>
> I want to measure the frequency difference between a 10 MHz OCXO and a
>> 10 MHz Rubidium.
>> I think that's what many people here have done many times... but i don't
>> want to use expensive
>> equipment like time interval counters with picosecond resolution etc. I
>> would prefer a cheap and
>> easy solution. I also would like to have an update rate of more than 1
>> measurement per second,
>> or even more.
>>
>> My first approach was to use a simple XOR phase comparator. I tried a
>> 74HCT86 and a 74HCT4046.
>> It works, but it's very noisy, so i don't get better than about 10 mHz
>> frequency resolution.
>> If i look at the lowpass-filtered output i don't see a nice sine or
>> triangular wave, but it looks more
>> than a triangular wave with round tops and some bumps between them.
>> Another problem is that the
>> difference frequency gets very low when the frequencies are very close,
>> so it's not enough to look
>> only for zero crossings of the difference signal.
>>
>> Does anybody know a possibility to get a resolution < 1 mHz ?
>>
>
> Have you looked at the PICTIC II project? It's not too bad.
>
> There is several other possible projects to consider, but the PICTIC II
> may be a good start. Also look at a divide down system such as the TADD 2
> divider or the just released TADD 2 Mini.
>
> There is a challenge in doing fairly high precission for low budget here
> on the list. Besides measuring frequency, we pride ourselves in measuring
> the frequency stability, Allan Deviation (ADEV), as good as possible.
>
> Cheers,
> Magnus
>
>
> _______________________________________________
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>
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