Counter Internal Oscillator Importance with External Reference?
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
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" <richard@karlquist.com> 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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Hi All;
Thanks for the input. Tom a question, was there any difference between the two 53230A oscillator when locked to an external reference? I have also experienced poor results with my 53230A often showing constant reference errors. Sadly I have several each 53230A's Ultra Stab and MCA3027's Med Stab so I cannot directly compare oscillator performance. I am trying to reverse engineer the Tektronix FCA/MCA counter to determine if there is away to directly feed an external reference is a direct reference instead of phase locking the internal reference while keeping the rest of the functionality intact, Which appears possible on these boxes. It appears U11B send off/on signals from pin 3,4,5 to switch between Std3, Oven5, or Rubidium4 internal ref which then provides 10MHz signals to U11B pin 204 RB ,205 Std,206 Oven respectively, What sense and controls that I have yet to determine, the selection may be in the menu. That may allow simple adding a connector and cable to the rear panel. U9A seems to relate PLL and switching. Perhaps the same is possible with the 53230A. I spoke with a friend Fred Walls today and asked if he though the internal reference was much of a factor when Lock to a good external reference and he did not thin so.
Thanks again for everyone's input.
Thomas Knox
From: time-nuts time-nuts-bounces@febo.com on behalf of Tom Van Baak tvb@LeapSecond.com
Sent: Tuesday, May 9, 2017 9:03 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Counter Internal Oscillator Importance with ExternalReference?
Hi Thomas,
About the 53230A -- like many of us I figured there was no point in buying the expensive OCXO versions since I have plenty of good 10 MHz references around here. So years ago Keysight loaned me two of them for a month: one with, and one without OCXO. Like most counters, the 53230A has an ext-ref input. But it is horrible. And the ref output is even worse. I think we've discussed this on the list before, including ADEV and PN plots. I decided not to buy one, ever, until they fixed the problem.
So it could be a nice counter. Someone at Agilent / Keysight needs to re-design the int/ext/mux/pll clock handling of the 53230A; someone who understands phase noise and short-term stability; someone who honors the intent of ext-ref-in and ref-out; someone who keeps stupid microprocessor / LCD / comms / power supply noise out of the clock path. Meanwhile I keep my old 53132A's and older SR620's and stay away from the 53230A.
If you have your own measurements, please share. Maybe I just got a bad sample, I don't know. But the ext-ref performance smelled like poor engineering to me. My hope is that someone on the list will hack a 53230A, fix the problem, and share the solution with us, or even with Keysight.
/tvb
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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Hi,
Like most counters, the 53230A has an ext-ref input. But it is horrible.
And the ref output is even worse.
I had similar issues using the ext ref. output of the Agilent 53230A
connected to the Ext. ref input of the 33220A. The frequency synthtized by
the 33220A had pretty bad ADEV values (measured by the 53220A).
I solved it by connecting the chassis of both instruments using the rear
earth cable screw of the two instrumens. The ADEV measured was limited by
the counter resolution (see attachment)
If I have time I'll try to do the opposite, use the free-running 33220A as
reference for the ext ref. input of the 53220A. Indeed, some noise inside
53220a may be cancel out due to the setup, but I don't have another good
counter right now :(
cheers,
Mattia
2017-05-09 17:03 GMT+02:00 Tom Van Baak tvb@leapsecond.com:
Hi Thomas,
About the 53230A -- like many of us I figured there was no point in buying
the expensive OCXO versions since I have plenty of good 10 MHz references
around here. So years ago Keysight loaned me two of them for a month: one
with, and one without OCXO. Like most counters, the 53230A has an ext-ref
input. But it is horrible. And the ref output is even worse. I think we've
discussed this on the list before, including ADEV and PN plots. I decided
not to buy one, ever, until they fixed the problem.
So it could be a nice counter. Someone at Agilent / Keysight needs to
re-design the int/ext/mux/pll clock handling of the 53230A; someone who
understands phase noise and short-term stability; someone who honors the
intent of ext-ref-in and ref-out; someone who keeps stupid microprocessor /
LCD / comms / power supply noise out of the clock path. Meanwhile I keep my
old 53132A's and older SR620's and stay away from the 53230A.
If you have your own measurements, please share. Maybe I just got a bad
sample, I don't know. But the ext-ref performance smelled like poor
engineering to me. My hope is that someone on the list will hack a 53230A,
fix the problem, and share the solution with us, or even with Keysight.
/tvb
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
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.
Hi All;
I used my speech recognition software last night and reading my post this morning I was embarrassed. Hopefully this email will make sense.
Thanks everyone for their input. Tom, i have a question; was there any difference between the two 53230A oscillators when locked to an external reference? I have also experienced poor results with my 53230A HS phase locked to an external reference. My issue is constant pop-ups showing reference errors. I wonder if that is related to issues you encountered. I would like to compare oscillator options in the same counter model and I have several each 53230A's and MCA3027's but sadly they have the same oscillator option in each respectively so I cannot directly compare PLL oscillator performance. My thinking is a phase locked internal reference may not be the best option for those of us with ULPN, Ultra Stable house references so I am trying to reverse engineer the Tektronix FCA/MCA counter to determine if there is away to directly feed an external reference instead of phase locking the internal reference. My plan is to find a way (if possible and it is encouraging) to do this while keeping the rest of the functionality intact, Which does appear possible on the Tektronix, Fluke, Pendulum instruments (All the same base units branded differently). It appears depending on the oscillator option U11B sends an off/on signals to switch between internal oscillator options; Std Pin3, Oven Pin5, or Rubidium Pin4. This switching then has the installed reference option provides 10MHz signals to U11B pin204 RB, Pin205 Std, Pin206 Oven respectively, most likely changing PLL parameters at the same time. Whether this is auto sensed or manually controlled I have yet to determine. The selection may be in the menu. My thinking is this may allow simply adding a connector and cable to the rear panel to apply an external reference directly. In these counters U9A seems related to the PLL functions including control, sensing, and switching using the standard External Reference input. If my idea pans out this feature would remain unchanged so the internal oscillator can still be used (When the direct feed is not appropriate) to clean up a dirtier external reference. My plan is (Unless someone else has already looked into this is to next see if the same is also possible with the 53230A. The BIG question does this improve performance. Any thoughts? I spoke with a friend Fred Walls today and asked if he though the internal reference was much of a factor when Lock to a good external reference and he did not thin so. So I will keep anyone interested informed with my progress since I am sure many of you have reference that may benefit from this modification if it does improve performance.
Thanks again for everyone's input.
Thomas Knox
From: time-nuts time-nuts-bounces@febo.com on behalf of Tom Van Baak tvb@LeapSecond.com
Sent: Tuesday, May 9, 2017 9:03 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Counter Internal Oscillator Importance with ExternalReference?
Hi Thomas,
About the 53230A -- like many of us I figured there was no point in buying the expensive OCXO versions since I have plenty of good 10 MHz references around here. So years ago Keysight loaned me two of them for a month: one with, and one without OCXO. Like most counters, the 53230A has an ext-ref input. But it is horrible. And the ref output is even worse. I think we've discussed this on the list before, including ADEV and PN plots. I decided not to buy one, ever, until they fixed the problem.
So it could be a nice counter. Someone at Agilent / Keysight needs to re-design the int/ext/mux/pll clock handling of the 53230A; someone who understands phase noise and short-term stability; someone who honors the intent of ext-ref-in and ref-out; someone who keeps stupid microprocessor / LCD / comms / power supply noise out of the clock path. Meanwhile I keep my old 53132A's and older SR620's and stay away from the 53230A.
If you have your own measurements, please share. Maybe I just got a bad sample, I don't know. But the ext-ref performance smelled like poor engineering to me. My hope is that someone on the list will hack a 53230A, fix the problem, and share the solution with us, or even with Keysight.
/tvb
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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Hi Thomas,
On 05/10/2017 07:12 PM, Tom Knox wrote:
Hi All;
I used my speech recognition software last night and reading my post
this morning I was embarrassed. Hopefully this email will make
sense. Thanks everyone for their input. Tom, i have a question; was
there any difference between the two 53230A oscillators when locked
to an external reference? I have also experienced poor results with
my 53230A HS phase locked to an external reference. My issue is
constant pop-ups showing reference errors. I wonder if that is
related to issues you encountered. I would like to compare oscillator
options in the same counter model and I have several each 53230A's
and MCA3027's but sadly they have the same oscillator option in each
respectively so I cannot directly compare PLL oscillator
performance.
I won't comment on the 53230A's as I haven't dug into them (yet).
My thinking is a phase locked internal reference may not be the best
option for those of us with ULPN, Ultra Stable house references so I
am trying to reverse engineer the Tektronix FCA/MCA counter to
determine if there is away to directly feed an external reference
instead of phase locking the internal reference. My plan is to find a
way (if possible and it is encouraging) to do this while kee ping the
rest of the functionality intact, Which does appear possible on the
Tektronix, Fluke, Pendulum instruments (All the same base units
branded differently). It appears depending on the oscillator option
U11B sends an off/on signals to switch between internal oscillator
options; Std Pin3, Oven Pin5, or Rubidium Pin4. This switching then
has the installed reference option provides 10MHz signals to U11B
pin204 RB, Pin205 Std, Pin206 Oven respectively, most likely changing
PLL parameters at the same time. Whether this is auto sensed or
manually controlled I have yet to determine. The selection may be in
the menu. My thinking is this may allow simply adding a connector and
cable to the rear panel to apply an external reference directly. In
these counters U9A seems related to the PLL functions including
control, sensing, and switching using the standard External Reference
input. If my idea pans out this feature would remain unchanged so the
internal oscillator can still be used ( When the direct feed is not
appropriate) to clean up a dirtier external reference. My plan is
(Unless someone else has already looked into this is to next see if
the same is also possible with the 53230A. The BIG question does this
improve performance. Any thoughts? I spoke with a friend Fred Walls
today and asked if he though the internal reference was much of a
factor when Lock to a good external reference and he did not thin so.
So I will keep anyone interested informed with my progress since I am
sure many of you have reference that may benefit from this
modification if it does improve performance.
Now, there is a PLL in the CNT-90/91 (Fluke IDs are PM6690/6691 and
Tektronix IDs are FCA-3000/3100) and that is to lock the 100 MHz
oscillator to whatever 10 MHz reference you got muxed in. The PLL chip
is U9A which is an ADF4001 and the 100 MHz oscillator is around U47A,
L3, C171, C177-C180 and D23. You need this setup, so you cannot bypass.
The FPGA does not to anything magic, there is first a mux to select
whatever internal 10 MHz reference there is, according to option. Then,
if it has external 10 MHz selected, it then selects that and outputs.
The ADF4001 is used as a phase-comparator and needed divide by 10 to
compare things. The Charge-Pump output has the traditional capacitor and
capitor/resistor chain, so there is your PI control-loop, which is
exactly what you would like to see there. It would track in due to first
degree thermal shift and I'd expect it to be sufficiently high bandwidth
not to cause any concern of interest.
The external clock input includes a crystal filter, which helps to shave
of disturbing sidebands.
I'm skeptical that there is much gain to be found in modifying that.
I know other designs have had problems, but I don't see that this one
should have any major reasons for concern. I could do some measures once
I'm back home.
If you have high-quality, low jitter/phase-noise 100 MHz, then you could
feed that into the counter too, but it may need the 10 MHz for some
things, I haven't checked all details yet to rule it out.
Still, I wonder if it is worth the trouble.
The designers knew where their main problems where, and this never
popped up as a big concern for them.
Thanks again for everyone's input.
Thanks for keeping us out of trouble. :)
Cheers,
Magnus
Hi,
Like most counters, the 53230A has an ext-ref input. But it is horrible.
And the ref output is even worse.
I had similar issues using the internal ref. output of the Agilent 53230A
(with OCXO option installed) connected to the Ext. ref input of the 33220A.
The frequency synthtized by the 33220A had pretty bad ADEV values (measured
by the 53220A).
I solved it by connecting the chassis of both instruments using the rear
earth cable screw of the two instrumens. The ADEV measured was limited by
the counter resolution (see [1] and [2])
If I have time I'll try to do the opposite, use the free-running 33220A as
reference for the ext ref. input of the 53220A. Indeed, some noise inside
53220a may be cancel out due to the setup, but I don't have another counter
with a good reference right now :(
cheers,
Mattia
[1] http://i68.tinypic.com/2ynrmaa.png
[2] http://i67.tinypic.com/hrf15i.png
(Message resent due to antispam, sorry for any duplicated message)
2017-05-09 17:03 GMT+02:00 Tom Van Baak tvb@leapsecond.com:
Hi Thomas,
About the 53230A -- like many of us I figured there was no point in buying
the expensive OCXO versions since I have plenty of good 10 MHz references
around here. So years ago Keysight loaned me two of them for a month: one
with, and one without OCXO. Like most counters, the 53230A has an ext-ref
input. But it is horrible. And the ref output is even worse. I think we've
discussed this on the list before, including ADEV and PN plots. I decided
not to buy one, ever, until they fixed the problem.
So it could be a nice counter. Someone at Agilent / Keysight needs to
re-design the int/ext/mux/pll clock handling of the 53230A; someone who
understands phase noise and short-term stability; someone who honors the
intent of ext-ref-in and ref-out; someone who keeps stupid microprocessor /
LCD / comms / power supply noise out of the clock path. Meanwhile I keep my
old 53132A's and older SR620's and stay away from the 53230A.
If you have your own measurements, please share. Maybe I just got a bad
sample, I don't know. But the ext-ref performance smelled like poor
engineering to me. My hope is that someone on the list will hack a 53230A,
fix the problem, and share the solution with us, or even with Keysight.
/tvb
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
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.