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What would be a reasonably cheap way of checking frequency calibration? I have an old hp 5328, with oven. I also have one of those cheap GPS modules where the PPS output can be reprogrammed. I set it to 1kHz and the counter showed 1.0000kHz. Sounds good?
There are u-blox modules that can be reprogrammed to output 10MHz and the 5328 can use an external 10MHz for timebase. Would such a module (below) work?
?
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Hi Anders, with my counters, I put a 10 MHz sinewave from the GPSDO (thunderbolt) on channel 1 of oscilloscope, triggering on it, then I put the counter's 10 MHz reference to channel 2 and I trim the reference until there's no (or barely) shifting of the timebase signal with respect to the fixed (triggering) 10 MHz from GPSDO. HTH Frank IZ8DWF On Tue, Oct 10, 2017 at 1:58 PM, anders.gustafsson@... [hp_agilent_equipment] <hp_agilent_equipment@...> wrote:
What would be a reasonably cheap way of checking frequency calibration? I have an old hp 5328, with oven. I also have one of those cheap GPS modules where the PPS output can be reprogrammed. I set it to 1kHz and the counter showed 1.0000kHz. Sounds good?
There are u-blox modules that can be reprogrammed to output 10MHz and the 5328 can use an external 10MHz for timebase. Would such a module (below) work?
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Ok. So you have a Trrimble Thunderbolt GPS??
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I can't recall where, but someone posted a comment to the effect that the PPS output of their GPS unit had significant (~20 nS) jitter.
I'd suggest feeding the output of the reference to be checked to an MCU such as an STM32F4xx Discovery board along with the PPS from the GPS and counting the number of transitions between PPS outputs.
Have Fun!
Reg
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By far and away the best choice is going to be a GPS disciplined oscillator such as an HP 3801A or a Thunderbolt. A good GPSDO should be good to at least 1x10^-10 ? (1ppb) over the course of a day. ? It will be the simplest as well. Take the 10MHz output and feed into the Ext Reference input on pretty much all of your lab equipment. Any good counter, signal generator, even bench scopes will have one. A simple video distribution amplifier will serve just fine to ship the signal to all of them at once. Don't forget to put one on the workbench someplace to plug it into whatever you are working on. :)
There are a variety of ways to to check the accuracy of your reference. One of the better ones is to look at jitter and phase difference over time. Feed one into the trigger on a time interval counter such as an HP5370 , the other into the input. The time interval between the two shouldn't change (it will), but the change over time and the jitter between the two will be very instructive. Using this, you can see changes over the course of days or weeks (depending on what data you save). There is a good HP App Note on jitter.
Another is feed one into X, one into Y of an oscilloscope. In phase is a circle. Out of phase is a diagonal line.? frequency multiples will show pretty patterns from your favorite SciFi movies of the 50's and 60's.
This is a subject many have been drawn into very deeply. There is, in fact an entire mailing list devoted to the subject.
Beware however. It is a subject that can cost you a great deal of time and money. A man with one watch knows what time it is. A man with two is never sure. A man with 3 can make a very good guess however! That thinking can lead to owning several GPSDO's, a rubidium, and a cesium beam standard. Or several of each. Really. And taking your kids up mountains to prove relativity. Really. .
Bob
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I can't recall where, but someone posted a comment to the effect that the PPS output of their GPS unit had significant (~20 nS) jitter.
I'd suggest feeding the output of the reference to be checked to an MCU such as an STM32F4xx Discovery board along with the PPS from the GPS and counting the number of transitions between PPS outputs.
Have Fun!
Reg
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?????? On a standard scope with the same signal on X and
Y in phase is a line at 45degrees to the right, 180degrees out of
phase is a straight line tilted 45 degrees to the left, a circle
is 90 degrees out of phase. This assumes equal phase response of
of the X and Y amplifiers in the scope.
????????? If there is drift the pattern will rotate.
On 10/10/2017 7:38 AM, Bob Bownes
bownes@... [hp_agilent_equipment] wrote:
???
Another is feed one into X, one into
Y of an oscilloscope. In phase is a circle. Out of phase
is a diagonal line.???
frequency multiples will show pretty
patterns from your favorite SciFi movies of the 50's and
60's.
--
Richard Knoppow
dickburk@...
WB6KBL
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Correct! Need more caffeinated beverage. Thanks!
?
?? On a standard scope with the same signal on X and
Y in phase is a line at 45degrees to the right, 180degrees out of
phase is a straight line tilted 45 degrees to the left, a circle
is 90 degrees out of phase. This assumes equal phase response of
of the X and Y amplifiers in the scope.
??? If there is drift the pattern will rotate.
On 10/10/2017 7:38 AM, Bob Bownes
bownes@... [hp_agilent_equipment] wrote:
?
Another is feed one into X, one into
Y of an oscilloscope. In phase is a circle. Out of phase
is a diagonal line.?
frequency multiples will show pretty
patterns from your favorite SciFi movies of the 50's and
60's.
--
Richard Knoppow
dickburk@...
WB6KBL
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Two questions for the original poster: How accurate do you need (want) to be? and what are you using the counter for?
Time and frequency precision can become an obsession - Time Nuttery.
Robert G8RPI.
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?????? There are many of us who are slaves to coffee.
Have few other bad habits but I can't even talk in the morning
before drinking a cup.
On 10/10/2017 11:02 AM, Bob Bownes
bownes@... [hp_agilent_equipment] wrote:
Correct!
Need more caffeinated beverage. Thanks!
--
Richard Knoppow
dickburk@...
WB6KBL
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They say coffee helps you live longer, I don’t know about how true that is but I do know that it definitely makes me enjoy the time I do have much more!
toggle quoted message
Show quoted text
?
?? There are many of us who are slaves to coffee.
Have few other bad habits but I can't even talk in the morning
before drinking a cup.
On 10/10/2017 11:02 AM, Bob Bownes
bownes@... [hp_agilent_equipment] wrote:
Correct!
Need more caffeinated beverage. Thanks!
--
Richard Knoppow
dickburk@...
WB6KBL
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I have the same equipment and don't need insane accuracy (1Hz in 100MHz is more the sufficient - 10e-8). ?I will put the 1PPS signal into the A input, the 10MHz from the ref osc out on the back into the B input and use the B/A ratio mode and set the resolution to get the desired LSD resolution. ? It will pretty much stay on 10000000.0 for hours with an occaisional blip up or down the LSD. ?When it jitters up as often as down, I'm close enough for my hobby use. ?Better signal lock results in less jitter (outdoor antenna is better than one of those fingernail sized things indoors).
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What's wrong with my Rubidium reference that would make me choose a GPS disciplined? Costed me $75 on EPay, but still needs a power supply, case and diastribution amplifiers, yet another project to boot...
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Unless there is a reason for extreme precision in your frequency measuring, you don't need to spend too much money adjusting the oscillator to a reasonable precision. The old method using WWV with a radio receiver can be quite good.?
I have been using GPS for the last dozen years and before that WWVB on 60 kHz, but I do a lot of work requiring high accuracy at microwave frequencies.
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I recently bought an all new (small) 10 MHz output GPS receiver, used for work away from my lab. It is made in China, and comes with a power supply (small "wall-wart") and antenna for $130 delivered (eBay item?262981677836). This provides far better accuracy than any reasonable person would probably need, at the cost of a new crystal oven. The construction appears to be excellent. It locks quickly even with the antenna on the work bench.
Stuart
K6YAZ
West Hills, (Los Angeles)
California
StuartL73@...
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Right there with ya.. -Dave On 10/10/2017 04:11 PM, `Richard Knoppow dickburk@... [hp_agilent_equipment] wrote:
?????? There are many of us who are slaves to coffee. Have few other bad
habits but I can't even talk in the morning before drinking a cup.
On 10/10/2017 11:02 AM, Bob Bownes bownes@...
[hp_agilent_equipment] wrote:
Correct! Need more caffeinated beverage. Thanks!
--
Richard Knoppow
dickburk@...
WB6KBL
-- Dave McGuire, AK4HZ New Kensington, PA
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Thanks to all that responded. I am playing with a receiver for Navtex. Problem there is that the nearest station only transmits for 10 minutes (max) every four hours so that makes tuning the receiver part a bit awkward.
Hence I need to be able to use a RF generator instead and a counter to make sure my LO and IFs are correct. The detector has narrow filters in DSP so accuracy is important. Nevertheless 1/1000 should suffice for me.
With the simple setup I have now (simple GPS, 1kHz) I know that the counter is fairly accurate so I assume that if it is acurate on 1kHz, then it should be accurate on 518kHz as well.
Thanks Stuart for the tip of the eBay receiver. I have seen those, but did not know if they were any good. I take your comment as a vote of confidence, so I might end up buying one.
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We need extreme freq stability for our master freq reference for a particle accelerator that is 770 meters long.? The original 46 year old oscillator was first a HP107BR special that was at 6.289xxxx MHz, then multiplied up with a TCI multiplier assembly. Later it was HP105B, again special crystal in double oven setup. Backup was a Vectron oscillator. Four years ago, a digital engineer replaced the crystal sources with a Meridian End Run GPS-disciplined oscillator and a TCI phase locked assembly with multipliers. This is used to generate a 100.625 Mhz, 201.25 Mhz and 805 MHz reference. With phase stability giving trouble, I took to comparing the GPS ultra-stable reference to the HP105B, 10 MHz vs 6.289xxxx. I used a HP 5372A dual channel frequency analyzer, and recorded histograms and stats of each oscillator. The GPS-disciplined oscillators are clearly inferior by a factor of 10 for medium term stability over a few hours. Two of them were tested. Then I found an old Racal Rubidium oscillator in VXI format. It works great. The moral of this story is, specs on paper aren't always enough. The GPS oscillators claimed 10^-11 and such, over 24 hours. But over shorter term even, they jumped around and covered a few millihertz spread. Stanford Research has a nice crystal oscillator that is also available as a Rubidium oscillator option. These are not very expensive.
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"Not very expensive" as in "compared to buying a particle accelerator" ? ;)
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I liked the
story about the man with 3 watches. This is what measurement is all about, making
a conclusion of the data that you have. The measurements give you an indication
of the precision you have but not much about accuracy. Your data can be off by
x ppm, and you can not tell…
G?ran
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You need to investigate, and measure Allen Variance, a better
indication of the quality of an oscillator. What you will most
likely find is the GPS disciplined oscillator, though very good
in terms of "accuracy", is poor for short term Allen Variance,
and that the HP 107 is very good for short term Allen Variance,
and poor for long term Allen Variance.
This path is well trodden for a group of people that are known
as timenuts, and they have a group of their own where they
discuss such things.
-Chuck Harris
jtml@... [hp_agilent_equipment] wrote:
toggle quoted message
Show quoted text
We need extreme freq stability for our master freq reference for a particle accelerator that is 770 meters long. The original 46 year old oscillator was first a HP107BR special that was at 6.289xxxx MHz, then multiplied up with a TCI multiplier assembly. Later it was HP105B, again special crystal in double oven setup. Backup was a Vectron oscillator. Four years ago, a digital engineer replaced the crystal sources with a Meridian End Run GPS-disciplined oscillator and a TCI phase locked assembly with multipliers. This is used to generate a 100.625 Mhz, 201.25 Mhz and 805 MHz reference. With phase stability giving trouble, I took to comparing the GPS ultra-stable reference to the HP105B, 10 MHz vs 6.289xxxx. I used a HP 5372A dual channel frequency analyzer, and recorded histograms and stats of each oscillator. The GPS-disciplined oscillators are clearly inferior by a factor of 10 for medium term stability over a few hours. Two of them were tested. Then I found an old Racal Rubidium oscillator in VXI format. It works great. The moral of this story is, specs on paper aren't always enough. The GPS oscillators claimed 10^-11 and such, over 24 hours. But over shorter term even, they jumped around and covered a few millihertz spread. Stanford Research has a nice crystal oscillator that is also available as a Rubidium oscillator option. These are not very expensive.
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Anders
bownes
Dave McGuire
G?ran Krusell