Re: [time-nuts] Counter Internal Oscillator Importance with External Reference?

[Bruce Griffiths]

CERN have flagged another potential issue with the 53230A in that every so 
often seemingly randomly communications go hawire.

Bruce 

> 
> On 10 May 2017 at 04:46 "Richard (Rick) Karlquist" 
>  wrote:
> 
> On 5/9/2017 12:05 AM, Poul-Henning Kamp wrote:
> >
> 
> > > 
> > I'm sure that modern counters like 53230 are better at this than
> > 
> > > 
> The 53230 oven oscillator option in an inferior oscillator to
> the 10811, by an order of magnitude. So in this case,
> modern != better.
> 
> Rick
> 
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Re: [time-nuts] Counter Internal Oscillator Importance with External Reference?

[Richard (Rick) Karlquist]

On 5/9/2017 12:05 AM, Poul-Henning Kamp wrote:


I'm sure that modern counters like 53230 are better at this than


The 53230 oven oscillator option in an inferior oscillator to
the 10811, by an order of magnitude.  So in this case,
modern != better.

Rick
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Re: [time-nuts] Counter Internal Oscillator Importance with External Reference?

[Poul-Henning Kamp]

In message <54ee7bdd-0a49-cc49-540d-2812e70dd...@rubidium.dyndns.org>, Magnus 
Danielson writes:

>Wither it is proper side bands or other systematic noise, it is bad 
>indeed, [...]

It's more subtle than that, it can be things like thresholds in
the counters trigger being sensitive to the phase of the internal
clock because of (very slight) cross-talk.

I reported data on this a couple of years ago, as I recall my setup
were something like this:

House-10MHz --> HP3336C clk-in and HP5370B clk-in.

HP3336C output -> HP5370B start then 3m coax then HP5370B stop.

Measure TI(start->stop), for different settings of output phase angle on the 
HP3336C.

Theoretically that plot should be a flat line.

In practice it is not even close.

I think I convinced myself that the majority of the problem was trigger-noise 
the HP5370B,
but my notes are not accessible at this time.

-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@freebsd.org | TCP/IP since RFC 956
FreeBSD committer   | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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Re: [time-nuts] Counter Internal Oscillator Importance with External Reference?

[Magnus Danielson]

Hi Poul-Henning,

On 05/09/2017 02:39 PM, Poul-Henning Kamp wrote:


In message <60c74d75-41e5-7112-d8b6-721664b89...@rubidium.dyndns.org>, Magnus 
Danielson writes:


Indeed. On the other hand some measurements is hard not to do that way.
One should think about how isolation is created if needed, and this
includes AC and DC, common mode and differential mode. Isolation
amplifier should be part of the arsenal.


EMI is part of it, but there raw synchronism is a significant
source of systematic errors because the "noise" is no longer
gaussian.



Wither it is proper side bands or other systematic noise, it is bad 
indeed, that would be part of the RF differential mode disturbances.
This assumes the source is "clean", and if it is not it should not be 
used to start with. What remains is really issues from the setup, and 
that's when signal integrity/EMI care and isolation amplifiers comes in.


Cheers,
Magnus
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Re: [time-nuts] Counter Internal Oscillator Importance with External Reference?

[Magnus Danielson]

Hi,

In HP5370A/B you mux sources. In SR620 there is a lockup PLL, as far as 
I remember.


Cheers,
Magnus

On 05/09/2017 01:11 PM, Bob kb8tq wrote:

Hi

If you grab the schematic of pretty much any of these counters, you find a 
fairly common approach.
Somewhere inside is a VHF oscillator. The internal TCXO, OCXO, or Rb acts as a 
phase lock source
for that VHF oscillator. Typical PLL bandwidths are pretty low (10’s of Hz). 
When you put in an external
reference, it acts as the reference to the same PLL.

This does a couple of things. You take care of spurs on the external reference. 
That is the same
thing you do locking up a VHF oscillator to your GPSD for microwave work. You 
get the long term
accuracy (1 second and out) of the external reference. Your phase noise (and 
thus broadband mask
jitter) is improved.

Does every counter on the planet work this way? - of course not. Somewhere 
somebody did it a
different way. As long as they *did* do it this way, the internal reference 
does not matter once you
switch to an external standard. Even if they did it in some other way, if they 
did it right, the same
statement would apply.

Bob


On May 8, 2017, at 9:02 PM, Tom Knox  wrote:

Hi All;

How important is the standard, medium, or high stability reference in counters 
like the 53230A, or FCA3120 when locked to an ultra low phase noise external 
reference? Particularly when making measurements and adjustments on other ultra 
high performance references?

I know Agilent sold 53132A counters with an option (H01 I believe) that 
bypassed the internal reference completely when and external reference is 
applied, but I think standard configuration on most counter is to discipline 
the internal reference.

Thanks for your thoughts.

Thomas Knox

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Re: [time-nuts] Counter Internal Oscillator Importance with External Reference?

[Poul-Henning Kamp]

In message <60c74d75-41e5-7112-d8b6-721664b89...@rubidium.dyndns.org>, Magnus 
Danielson writes:

>Indeed. On the other hand some measurements is hard not to do that way.
>One should think about how isolation is created if needed, and this 
>includes AC and DC, common mode and differential mode. Isolation 
>amplifier should be part of the arsenal.

EMI is part of it, but there raw synchronism is a significant
source of systematic errors because the "noise" is no longer
gaussian.

-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@freebsd.org | TCP/IP since RFC 956
FreeBSD committer   | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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Re: [time-nuts] Counter Internal Oscillator Importance with External Reference?

[Bob kb8tq]

Hi

If you grab the schematic of pretty much any of these counters, you find a 
fairly common approach. 
Somewhere inside is a VHF oscillator. The internal TCXO, OCXO, or Rb acts as a 
phase lock source
for that VHF oscillator. Typical PLL bandwidths are pretty low (10’s of Hz). 
When you put in an external
reference, it acts as the reference to the same PLL. 

This does a couple of things. You take care of spurs on the external reference. 
That is the same 
thing you do locking up a VHF oscillator to your GPSD for microwave work. You 
get the long term
accuracy (1 second and out) of the external reference. Your phase noise (and 
thus broadband mask
jitter) is improved. 

Does every counter on the planet work this way? - of course not. Somewhere 
somebody did it a 
different way. As long as they *did* do it this way, the internal reference 
does not matter once you 
switch to an external standard. Even if they did it in some other way, if they 
did it right, the same 
statement would apply. 

Bob 

> On May 8, 2017, at 9:02 PM, Tom Knox  wrote:
> 
> Hi All;
> 
> How important is the standard, medium, or high stability reference in 
> counters like the 53230A, or FCA3120 when locked to an ultra low phase noise 
> external reference? Particularly when making measurements and adjustments on 
> other ultra high performance references?
> 
> I know Agilent sold 53132A counters with an option (H01 I believe) that 
> bypassed the internal reference completely when and external reference is 
> applied, but I think standard configuration on most counter is to discipline 
> the internal reference.
> 
> Thanks for your thoughts.
> 
> Thomas Knox
> 
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Re: [time-nuts] Counter Internal Oscillator Importance with External Reference?

[Magnus Danielson]

Hi,

On 05/09/2017 09:05 AM, Poul-Henning Kamp wrote:


In message , Magnus 
Danielson writes:


Also, there is a reason that you can buy different internal oscillators,
this is one of them. For labs with their frequency distribution there is
no need to waste money on stand-alone performance.


Please don't forget that running the counter of the same signal as
the circuits being measured runs the risk of masking noise processes.


Indeed. On the other hand some measurements is hard not to do that way.
One should think about how isolation is created if needed, and this 
includes AC and DC, common mode and differential mode. Isolation 
amplifier should be part of the arsenal.



I'm sure that modern counters like 53230 are better at this than
the 5370, but you should always sanity-check your measurements
using the counters internal, undisturbed timebase.


Indeed. When you think you have a risc of disturbance, please do 
measurements to verify the setup.


Cheers,
Magnus
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Re: [time-nuts] Counter Internal Oscillator Importance with External Reference?

[Poul-Henning Kamp]

In message , Magnus 
Danielson writes:

>Also, there is a reason that you can buy different internal oscillators, 
>this is one of them. For labs with their frequency distribution there is 
>no need to waste money on stand-alone performance.

Please don't forget that running the counter of the same signal as
the circuits being measured runs the risk of masking noise processes.

I'm sure that modern counters like 53230 are better at this than
the 5370, but you should always sanity-check your measurements
using the counters internal, undisturbed timebase.

-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@freebsd.org | TCP/IP since RFC 956
FreeBSD committer   | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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Re: [time-nuts] Counter Internal Oscillator Importance with External Reference?

[Magnus Danielson]

Hi Tom!

On 05/09/2017 03:02 AM, Tom Knox wrote:

Hi All;

How important is the standard, medium, or high stability reference in counters 
like the 53230A, or FCA3120 when locked to an ultra low phase noise external 
reference? Particularly when making measurements and adjustments on other ultra 
high performance references?

I know Agilent sold 53132A counters with an option (H01 I believe) that 
bypassed the internal reference completely when and external reference is 
applied, but I think standard configuration on most counter is to discipline 
the internal reference.

Thanks for your thoughts.


When you provide an external reference, the long term stability becomes 
relatively unimportant. Let's view the two cases:


1) Bypass internal oscillator: If you bypass the internal oscillator and 
always supply an external oscillator, don't waste money on the internal 
reference, it has no use.


2) Lock internal oscillator: If the oscillator is PLL steered, the short 
term noise, i.e. phase-noise, is of relevance, but the long-term only 
cares in the aspect that you can maintain lock, and you can probably 
trim the oscillator to every 5 years to ensure lock, but other than that 
you don't need to waste mony on it. If the phase noise is an issue, you 
could possibly see that in the datahseet/performance spec, but for all I 
have seen, only long term performance is given, so I'd say that you 
should not waste your money there either.


So, unless it will operate as a stand-alone, don't waste money on 
internal reference.


Also, there is a reason that you can buy different internal oscillators, 
this is one of them. For labs with their frequency distribution there is 
no need to waste money on stand-alone performance.


Look at the HP5335A for instance. Standard performance is an XO, and you 
need to trim that regularly to have any kind of performance. The high 
stability option is a 10811. That is quite a jump in performance.


Cheers,
Magnus
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[time-nuts] Counter Internal Oscillator Importance with External Reference?

[Tom Knox]

Hi All;

How important is the standard, medium, or high stability reference in counters 
like the 53230A, or FCA3120 when locked to an ultra low phase noise external 
reference? Particularly when making measurements and adjustments on other ultra 
high performance references?

I know Agilent sold 53132A counters with an option (H01 I believe) that 
bypassed the internal reference completely when and external reference is 
applied, but I think standard configuration on most counter is to discipline 
the internal reference.

Thanks for your thoughts.

Thomas Knox

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