Re: [time-nuts] FE-5650A option 58 tuning word for 10 MHz output

[Clint Jay]

Oh that's interesting,  I've not seen the non DDS version of the 5680 yet.

The frequency division for output in the non option  58 ones I've had hands
on was definitely done in a CPLD chip,  the DDS was "for internal use only"
 as far as I could tell.

On 10 Jan 2017 09:07, "wb6bnq"  wrote:

> Hi Clint,
>
> Actually there are two versions of the 5680.  The older version is exactly
> like the 5650 option 58 composition.  The newer version has the DDS as part
> of the signal generation for the physics package.  And it appears that they
> may be using an FPGA programmed as a divider to provide the output
> frequency.
>
> BillWB6BNQ
>
>
> Clint Jay wrote:
>
> Yes,  in the 5650 there's only DDS on opt 58,  in the 5680 there is one in
>> the main loop too,  my bad for not being precise/muddled.
>>
>> On 10 Jan 2017 01:43, "wb6bnq"  wrote:
>>
>>
>>
>>> HI Bob & Clint,
>>>
>>> If you look at the second message of this thread, I attached the manual
>>> that applies to Option 58.  Look at PDF page # 16 and you will see that
>>> there is no DDS in the physics package.  The DDS is only used down stream
>>> in some variations of the product such as the Option 58 being discussed.
>>>
>>> BillWB6BNQ
>>>
>>> Bob kb8tq wrote:
>>>
>>> Hi
>>>
>>>
 In most Rb’s (including the FE 56xx’s) the DDS is mixed with a fixed
 microwave frequency signal. The DDS only has to make up “part” of the
 total
 offset. You get
 roughly a three orders of magnitude improvement because of this. Rick
 has
 gone
 into all the gory details of why it gets done this way in talking about
 the 5071. It
 is the same thing on an Rb.
 So, your basic math is correct about a normal DDS. In this case you are
 in the
 PPT rather than PPB range due to the multiplication.
 Bob






> On Jan 9, 2017, at 10:40 AM, Scott Stobbe 
> wrote:
>
> A 32-bit DDS synthesizing at 1/5 Fs, yields a tuning resolution of ~ 1
> ppb.
> So, I would imagine a slightly lower frequency is programmed into the
> DDS
> and the c-field is trimmed to yield a higher precision. If the new
> synthesized tone you wish to generate is an integer number of DDS codes
> you
> could start by assuming the c-field is trimmed to be on frequency, but
> if
> the new tone is a fractional number of 32-bit DDS codes you will have
> to
> manually trim if you want higher precision.
>
> On Mon, Jan 9, 2017 at 4:48 AM, wb6bnq  wrote:
>
>
>
>
>
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Re: [time-nuts] FE-5650A option 58 tuning word for 10 MHz output

[wb6bnq]

Hi Clint,

Actually there are two versions of the 5680.  The older version is 
exactly like the 5650 option 58 composition.  The newer version has the 
DDS as part of the signal generation for the physics package.  And it 
appears that they may be using an FPGA programmed as a divider to 
provide the output frequency.


BillWB6BNQ


Clint Jay wrote:


Yes,  in the 5650 there's only DDS on opt 58,  in the 5680 there is one in
the main loop too,  my bad for not being precise/muddled.

On 10 Jan 2017 01:43, "wb6bnq"  wrote:

 


HI Bob & Clint,

If you look at the second message of this thread, I attached the manual
that applies to Option 58.  Look at PDF page # 16 and you will see that
there is no DDS in the physics package.  The DDS is only used down stream
in some variations of the product such as the Option 58 being discussed.

BillWB6BNQ

Bob kb8tq wrote:

Hi
   


In most Rb’s (including the FE 56xx’s) the DDS is mixed with a fixed
microwave frequency signal. The DDS only has to make up “part” of the total
offset. You get
roughly a three orders of magnitude improvement because of this. Rick has
gone
into all the gory details of why it gets done this way in talking about
the 5071. It
is the same thing on an Rb.
So, your basic math is correct about a normal DDS. In this case you are
in the
PPT rather than PPB range due to the multiplication.
Bob




 


On Jan 9, 2017, at 10:40 AM, Scott Stobbe 
wrote:

A 32-bit DDS synthesizing at 1/5 Fs, yields a tuning resolution of ~ 1
ppb.
So, I would imagine a slightly lower frequency is programmed into the DDS
and the c-field is trimmed to yield a higher precision. If the new
synthesized tone you wish to generate is an integer number of DDS codes
you
could start by assuming the c-field is trimmed to be on frequency, but if
the new tone is a fractional number of 32-bit DDS codes you will have to
manually trim if you want higher precision.

On Mon, Jan 9, 2017 at 4:48 AM, wb6bnq  wrote:



   


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Re: [time-nuts] FE-5650A option 58 tuning word for 10 MHz output

[Clint Jay]

Yes,  in the 5650 there's only DDS on opt 58,  in the 5680 there is one in
the main loop too,  my bad for not being precise/muddled.

On 10 Jan 2017 01:43, "wb6bnq"  wrote:

> HI Bob & Clint,
>
> If you look at the second message of this thread, I attached the manual
> that applies to Option 58.  Look at PDF page # 16 and you will see that
> there is no DDS in the physics package.  The DDS is only used down stream
> in some variations of the product such as the Option 58 being discussed.
>
> BillWB6BNQ
>
> Bob kb8tq wrote:
>
> Hi
>>
>> In most Rb’s (including the FE 56xx’s) the DDS is mixed with a fixed
>> microwave frequency signal. The DDS only has to make up “part” of the total
>> offset. You get
>> roughly a three orders of magnitude improvement because of this. Rick has
>> gone
>> into all the gory details of why it gets done this way in talking about
>> the 5071. It
>> is the same thing on an Rb.
>> So, your basic math is correct about a normal DDS. In this case you are
>> in the
>> PPT rather than PPB range due to the multiplication.
>> Bob
>>
>>
>>
>>
>>> On Jan 9, 2017, at 10:40 AM, Scott Stobbe 
>>> wrote:
>>>
>>> A 32-bit DDS synthesizing at 1/5 Fs, yields a tuning resolution of ~ 1
>>> ppb.
>>> So, I would imagine a slightly lower frequency is programmed into the DDS
>>> and the c-field is trimmed to yield a higher precision. If the new
>>> synthesized tone you wish to generate is an integer number of DDS codes
>>> you
>>> could start by assuming the c-field is trimmed to be on frequency, but if
>>> the new tone is a fractional number of 32-bit DDS codes you will have to
>>> manually trim if you want higher precision.
>>>
>>> On Mon, Jan 9, 2017 at 4:48 AM, wb6bnq  wrote:
>>>
>>>
>>>
>>
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>>
>>
>
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Re: [time-nuts] FE-5650A option 58 tuning word for 10 MHz output

[wb6bnq]

HI Bob & Clint,

If you look at the second message of this thread, I attached the manual 
that applies to Option 58.  Look at PDF page # 16 and you will see that 
there is no DDS in the physics package.  The DDS is only used down 
stream in some variations of the product such as the Option 58 being 
discussed.


BillWB6BNQ 



Bob kb8tq wrote:


Hi

In most Rb’s (including the FE 56xx’s) the DDS is mixed with a fixed microwave 
frequency signal. The DDS only has to make up “part” of the total offset. You get

roughly a three orders of magnitude improvement because of this. Rick has gone
into all the gory details of why it gets done this way in talking about the 
5071. It
is the same thing on an Rb. 


So, your basic math is correct about a normal DDS. In this case you are in the
PPT rather than PPB range due to the multiplication. 


Bob


 


On Jan 9, 2017, at 10:40 AM, Scott Stobbe  wrote:

A 32-bit DDS synthesizing at 1/5 Fs, yields a tuning resolution of ~ 1 ppb.
So, I would imagine a slightly lower frequency is programmed into the DDS
and the c-field is trimmed to yield a higher precision. If the new
synthesized tone you wish to generate is an integer number of DDS codes you
could start by assuming the c-field is trimmed to be on frequency, but if
the new tone is a fractional number of 32-bit DDS codes you will have to
manually trim if you want higher precision.

On Mon, Jan 9, 2017 at 4:48 AM, wb6bnq  wrote:

   



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Re: [time-nuts] FE-5650A option 58 tuning word for 10 MHz output

[Clint Jay]

Option 58 in a FE Rb is an additional sub board which has nothing to do
with the physics package control loop.

In an option 58 Rb there are two DDS chips.




On 9 January 2017 at 17:48, Scott Stobbe  wrote:

> It very well could be. Based on Marks comments, it sounds like the DDS tone
> after being squared up is directly driving a 23-bit counter for the 1 PPS
> output.
>
> On Mon, Jan 9, 2017 at 12:17 PM, Bob kb8tq  wrote:
>
> > Hi
> >
> > In most Rb’s (including the FE 56xx’s) the DDS is mixed with a fixed
> > microwave
> > frequency signal. The DDS only has to make up “part” of the total offset.
> > You get
> > roughly a three orders of magnitude improvement because of this. Rick has
> > gone
> > into all the gory details of why it gets done this way in talking about
> > the 5071. It
> > is the same thing on an Rb.
> >
> > So, your basic math is correct about a normal DDS. In this case you are
> in
> > the
> > PPT rather than PPB range due to the multiplication.
> >
> > Bob
> >
> >
> > > On Jan 9, 2017, at 10:40 AM, Scott Stobbe 
> > wrote:
> > >
> > > A 32-bit DDS synthesizing at 1/5 Fs, yields a tuning resolution of ~ 1
> > ppb.
> > > So, I would imagine a slightly lower frequency is programmed into the
> DDS
> > > and the c-field is trimmed to yield a higher precision. If the new
> > > synthesized tone you wish to generate is an integer number of DDS codes
> > you
> > > could start by assuming the c-field is trimmed to be on frequency, but
> if
> > > the new tone is a fractional number of 32-bit DDS codes you will have
> to
> > > manually trim if you want higher precision.
> > >
> > > On Mon, Jan 9, 2017 at 4:48 AM, wb6bnq  wrote:
> > >
> >
> > ___
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> > mailman/listinfo/time-nuts
> > and follow the instructions there.
> >
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-- 
Clint.

*No trees were harmed in the sending of this mail. However, a large number
of electrons were greatly inconvenienced.*
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Re: [time-nuts] FE-5650A option 58 tuning word for 10 MHz output

[Scott Stobbe]

It very well could be. Based on Marks comments, it sounds like the DDS tone
after being squared up is directly driving a 23-bit counter for the 1 PPS
output.

On Mon, Jan 9, 2017 at 12:17 PM, Bob kb8tq  wrote:

> Hi
>
> In most Rb’s (including the FE 56xx’s) the DDS is mixed with a fixed
> microwave
> frequency signal. The DDS only has to make up “part” of the total offset.
> You get
> roughly a three orders of magnitude improvement because of this. Rick has
> gone
> into all the gory details of why it gets done this way in talking about
> the 5071. It
> is the same thing on an Rb.
>
> So, your basic math is correct about a normal DDS. In this case you are in
> the
> PPT rather than PPB range due to the multiplication.
>
> Bob
>
>
> > On Jan 9, 2017, at 10:40 AM, Scott Stobbe 
> wrote:
> >
> > A 32-bit DDS synthesizing at 1/5 Fs, yields a tuning resolution of ~ 1
> ppb.
> > So, I would imagine a slightly lower frequency is programmed into the DDS
> > and the c-field is trimmed to yield a higher precision. If the new
> > synthesized tone you wish to generate is an integer number of DDS codes
> you
> > could start by assuming the c-field is trimmed to be on frequency, but if
> > the new tone is a fractional number of 32-bit DDS codes you will have to
> > manually trim if you want higher precision.
> >
> > On Mon, Jan 9, 2017 at 4:48 AM, wb6bnq  wrote:
> >
>
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Re: [time-nuts] FE-5650A option 58 tuning word for 10 MHz output

[Bob kb8tq]

Hi

In most Rb’s (including the FE 56xx’s) the DDS is mixed with a fixed microwave 
frequency signal. The DDS only has to make up “part” of the total offset. You 
get
roughly a three orders of magnitude improvement because of this. Rick has gone
into all the gory details of why it gets done this way in talking about the 
5071. It
is the same thing on an Rb. 

So, your basic math is correct about a normal DDS. In this case you are in the
PPT rather than PPB range due to the multiplication. 

Bob


> On Jan 9, 2017, at 10:40 AM, Scott Stobbe  wrote:
> 
> A 32-bit DDS synthesizing at 1/5 Fs, yields a tuning resolution of ~ 1 ppb.
> So, I would imagine a slightly lower frequency is programmed into the DDS
> and the c-field is trimmed to yield a higher precision. If the new
> synthesized tone you wish to generate is an integer number of DDS codes you
> could start by assuming the c-field is trimmed to be on frequency, but if
> the new tone is a fractional number of 32-bit DDS codes you will have to
> manually trim if you want higher precision.
> 
> On Mon, Jan 9, 2017 at 4:48 AM, wb6bnq  wrote:
> 

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Re: [time-nuts] FE-5650A option 58 tuning word for 10 MHz output

[Scott Stobbe]

A 32-bit DDS synthesizing at 1/5 Fs, yields a tuning resolution of ~ 1 ppb.
So, I would imagine a slightly lower frequency is programmed into the DDS
and the c-field is trimmed to yield a higher precision. If the new
synthesized tone you wish to generate is an integer number of DDS codes you
could start by assuming the c-field is trimmed to be on frequency, but if
the new tone is a fractional number of 32-bit DDS codes you will have to
manually trim if you want higher precision.

On Mon, Jan 9, 2017 at 4:48 AM, wb6bnq  wrote:

> Hi Matt,
>
> Well, after rereading Mark’s paragraph in question, I think he did not
> properly develop his complete thoughts.  The first statement about the
> Hydrogen Maser is absolute.  The second statement is the one that is really
> vague.  The third statement is the clue taken with the fact that the first
> sentence states the purpose of being used as a general purpose programmable
> frequency synthesizer.
>
> So the answer is leaving the C-field pot untouched and taking the
> difference between the “R” value and the “needed” input frequency
> associated with the current “F” value to produce the original output
> frequency gives a correction term to be applied to the “R” value to produce
> the value you use to come up with the new “F” value used for determining
> the wanted output signal.
>
> {After thought sentence} The above is not all that clear either, oh well.
> Read on it becomes clearer.
>
> So lets go through the process and see if I can do this without screwing
> up.  The formula for the DDS chip to produce a desired output for a given
> system clock frequency is the following :
>
> FTW (in decimal) = (Desired Output Frequency x 2^n) / SYSCLK
>
> However, the need is to determine what the proper input frequency is to
> produce the 8388608 Hz with the given “F” value as the FTW (Frequency
> Tuning Word).  So the formula is the following:
>
> SYSCLK = (Desired Output Frequency x 2^n) / FTW (in decimal)
>
> In your reported numbers this produces :
> first 2^32 = 4,294,967,296 times desired output of 8,388,608 Hz =
> 36,028,797,018,963,968
>
> SYSCLK = (Desired Output Frequency x 2^n) / FTW
> (in decimal)
> 50,255,055.809934059845495428970822 Hz = 36,028,797,018,963,968 /
> 716918854
>
> So the above 50 MHz number (SYSCLK) is the result of adjusting the C-field
> so the unit is “ON” frequency for the expected 1 Hz output from the
> factory.  This is the SYSCLK value that should be used to find the new “F”
> value for the DDS upon selecting a new output frequency such as 10 MHz (or
> as close as possible without touching the C-field) if that is your wanted
> output value.
>
> Actually, now that I have done the exercise, computing the delta between
> the “R” value and the above 50 MHz makes no sense and serves no purpose.  I
> cannot stress enough.  This is all predicated on not touching the C-field
> adjustment and assuming the 1 Hz signal is precisely on frequency.
>
> This method does not give a lot of confidence as to preciseness.  The real
> value in these Rb units is they have a much lower drift rate than a
> reasonably good quality Quartz oscillator.  Typically less then parts in 10
> to the minus 10th or minus 11th per month.
>
> BillWB6BNQ
>
>
>
>
>
> Mathias Weyland wrote:
>
> On 2017-01-04 10:16, wb6bnq wrote:
>>
>> Hello Bill
>>
>> Thanks for re-iterating over this.
>>
>>
>>  Yes, I do think the outer can covering is a MU-metal shield.  The
>>> bottom plate where the connector is located is not.
>>>
>>
>>
>> That is reassuring thank you!
>>
>>
>>  I know the calculator that comes with Windows XP will produce the
>>> correct mathematical results.  I think the Windows version 7 does the
>>> same.  I do not have Windows 10 and therefore cannot address that
>>> one, if there is one.  Even EXCEL spreadsheet does not do the job
>>> properly.  So use caution with your calculations.
>>>
>>
>>
>> OK noted. The original calculations were done with a calculator that
>> was designed for high precision (in the floating point sense). I did
>> re-run the calculations in windows calculator for kicks, and the
>> result is different, although the difference is too small to have an
>> effect on the integer phase accumulator increment (fingers crossed!)
>>
>>
>>  However, with all that said, it means nothing if you cannot properly
>>> measure the final value against an external standard of greater
>>> accuracy.  Acquiring the equipment to do the external measurements is
>>> where the real cost comes in.
>>>
>>
>>
>> Yes, I think that I am aware of that and I have the opportunity to
>> do that with somebody else's gear. I also understand that I'm supposed
>> to do that on a regular basis.
>>
>>
>>  Hopefully the above helps to clear up your query ?
>>>
>>
>>
>> Yes most of it is clear, thank you. Unfortunately though my original
>> question, i.e. how to incorporate the reported R value into the
>> calculation, is still kind of open. I'm 

Re: [time-nuts] FE-5650A option 58 tuning word for 10 MHz output

[wb6bnq]

Hi Matt,

Well, after rereading Mark’s paragraph in question, I think he did not 
properly develop his complete thoughts.  The first statement about the 
Hydrogen Maser is absolute.  The second statement is the one that is 
really vague.  The third statement is the clue taken with the fact that 
the first sentence states the purpose of being used as a general purpose 
programmable frequency synthesizer.


So the answer is leaving the C-field pot untouched and taking the 
difference between the “R” value and the “needed” input frequency 
associated with the current “F” value to produce the original output 
frequency gives a correction term to be applied to the “R” value to 
produce the value you use to come up with the new “F” value used for 
determining the wanted output signal.


{After thought sentence} The above is not all that clear either, oh 
well.  Read on it becomes clearer.


So lets go through the process and see if I can do this without screwing 
up.  The formula for the DDS chip to produce a desired output for a 
given system clock frequency is the following :


FTW (in decimal) = (Desired Output Frequency x 2^n) / SYSCLK

However, the need is to determine what the proper input frequency is to 
produce the 8388608 Hz with the given “F” value as the FTW (Frequency 
Tuning Word).  So the formula is the following:


SYSCLK = (Desired Output Frequency x 2^n) / FTW (in decimal)

In your reported numbers this produces :
first 2^32 = 4,294,967,296 times desired output of 8,388,608 Hz = 
36,028,797,018,963,968


SYSCLK = (Desired Output Frequency x 2^n) / FTW 
(in decimal)

50,255,055.809934059845495428970822 Hz = 36,028,797,018,963,968 / 716918854

So the above 50 MHz number (SYSCLK) is the result of adjusting the 
C-field so the unit is “ON” frequency for the expected 1 Hz output from 
the factory.  This is the SYSCLK value that should be used to find the 
new “F” value for the DDS upon selecting a new output frequency such as 
10 MHz (or as close as possible without touching the C-field) if that is 
your wanted output value.


Actually, now that I have done the exercise, computing the delta between 
the “R” value and the above 50 MHz makes no sense and serves no 
purpose.  I cannot stress enough.  This is all predicated on not 
touching the C-field adjustment and assuming the 1 Hz signal is 
precisely on frequency.


This method does not give a lot of confidence as to preciseness.  The 
real value in these Rb units is they have a much lower drift rate than a 
reasonably good quality Quartz oscillator.  Typically less then parts in 
10 to the minus 10th or minus 11th per month.


BillWB6BNQ





Mathias Weyland wrote:


On 2017-01-04 10:16, wb6bnq wrote:

Hello Bill

Thanks for re-iterating over this.



 Yes, I do think the outer can covering is a MU-metal shield.  The
bottom plate where the connector is located is not.



That is reassuring thank you!



 I know the calculator that comes with Windows XP will produce the
correct mathematical results.  I think the Windows version 7 does the
same.  I do not have Windows 10 and therefore cannot address that
one, if there is one.  Even EXCEL spreadsheet does not do the job
properly.  So use caution with your calculations.



OK noted. The original calculations were done with a calculator that
was designed for high precision (in the floating point sense). I did
re-run the calculations in windows calculator for kicks, and the
result is different, although the difference is too small to have an
effect on the integer phase accumulator increment (fingers crossed!)



 However, with all that said, it means nothing if you cannot properly
measure the final value against an external standard of greater
accuracy.  Acquiring the equipment to do the external measurements is
where the real cost comes in.



Yes, I think that I am aware of that and I have the opportunity to
do that with somebody else's gear. I also understand that I'm supposed
to do that on a regular basis.



 Hopefully the above helps to clear up your query ?



Yes most of it is clear, thank you. Unfortunately though my original
question, i.e. how to incorporate the reported R value into the
calculation, is still kind of open. I'm still convinced that what I
did, i.e. not taking the R number into account, is no worse than
using it. But this might be incorrect, and if it is I'd like to know
why.

Regards and thanks again

Matt
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Re: [time-nuts] FE-5650A option 58 tuning word for 10 MHz output

[Mathias Weyland]

On 2017-01-04 10:16, wb6bnq wrote:

Hello Bill

Thanks for re-iterating over this.



 Yes, I do think the outer can covering is a MU-metal shield.  The
bottom plate where the connector is located is not.


That is reassuring thank you!



 I know the calculator that comes with Windows XP will produce the
correct mathematical results.  I think the Windows version 7 does the
same.  I do not have Windows 10 and therefore cannot address that
one, if there is one.  Even EXCEL spreadsheet does not do the job
properly.  So use caution with your calculations.


OK noted. The original calculations were done with a calculator that
was designed for high precision (in the floating point sense). I did
re-run the calculations in windows calculator for kicks, and the
result is different, although the difference is too small to have an
effect on the integer phase accumulator increment (fingers crossed!)



 However, with all that said, it means nothing if you cannot properly
measure the final value against an external standard of greater
accuracy.  Acquiring the equipment to do the external measurements is
where the real cost comes in.


Yes, I think that I am aware of that and I have the opportunity to
do that with somebody else's gear. I also understand that I'm supposed
to do that on a regular basis.



 Hopefully the above helps to clear up your query ?


Yes most of it is clear, thank you. Unfortunately though my original
question, i.e. how to incorporate the reported R value into the
calculation, is still kind of open. I'm still convinced that what I
did, i.e. not taking the R number into account, is no worse than
using it. But this might be incorrect, and if it is I'd like to know
why.

Regards and thanks again

Matt
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Re: [time-nuts] FE-5650A option 58 tuning word for 10 MHz output

[Mathias Weyland]

On 2017-01-04 11:08, Attila Kinali wrote:

Hoi Attila


So it's the usual curiosity and the need to have a reference for
your 23cm radios?


Yes exactly.


Advantage of an GPSDO over an Rb is that you know it's on frequency,
while with an Rb it can be off without you knowing it, if the
electronics or the physics package is defect.


This is in line with what I've read. Maybe the decision to go for the
Rb was not the best one but I don't think that it's that bad either.
I was offered the opportunity to calibrate my modified Rb standard
against a fellow ham's two 10 MHz standards and his GPSDO.



BTW: there is a whole new way of looking at statistics of time series
in the field of time and frequency control, which you might find 
interesting.
The NIST Technote 1337[1] and NIST special publication 1065[2] give a 
nice

overview of the methods applied.


This is very interesting thank you for sharing those!



Unfortunately, it's not that easy :-)
I don't know the exact construction of the FE-5650, but usually the 
physics
package is just a normal aluminium microwave cavity, without 
shielding.
The mu-metal shield is usually the housing of the whole device 
itself.


Hm I thought I had done my homework on this one but I never have
issues with being proven wrong. For what it's worth, here are two 
pictures

of the unit in question:

http://2.bp.blogspot.com/_8uoOi3ZInLQ/SdZfVfpcBaI/BB8/YvZ2-l0GhMI/s400/DSCN4592.JPG
http://www.dty.sakura.ne.jp/keisoku/rubidium/FE5650-2.jpg

The shiny face plate is where I would be drilling. For what it's worth,
it is very light, nonmagnetic, does not look like the mu-metal I've
seen in disassembled hard disks and very much looks like machined
aluminum... Would a compromised mu-metal shield show during calibration
if the standard was physically rotated?

Best regards and thank you

Matt
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Re: [time-nuts] FE-5650A option 58 tuning word for 10 MHz output

[wb6bnq]

Hello Mathias,

I did mis-speak.  You're correct that only 32 bits (8 hex digits) are 
used to program the DDS chip.  As Mark points out they store a 64 bit 
number and only use 56 bits but he does not elaborate on what is done 
with the bits beyond 32.  Also, after reviewing my comment on the “R” 
number, I see that I did not really convey what my mind was trying to 
compose.


Let me try again and see if I can be clearer.  The Rb physics package, 
itself, is an extremely narrow filter that, under certain conditions, is 
stable to some finite degree with an extremely small drift.  One 
function that can modify the filter is a magnetic field.  By shielding 
all external magnetic influences except for what is purposefully 
introduced, the finite frequency of this filter can be varied by a small 
amount.  This is what the C-field adjustment is doing.


Yes, I do think the outer can covering is a MU-metal shield.  The bottom 
plate where the connector is located is not.


A Rubidium frequency standard is a controllable crystal oscillator fed 
through the Rb filter with a feedback signal from the filter to keep the 
crystal oscillator centered on the Rb filter.  By making very small 
changes to the Rb filter, the crystal oscillator frequency can be 
steered.  Over the long term of many months the Rb filter is more stable 
than a crystal oscillator and thus becomes a higher level standard 
relative to a good crystal oscillator for the long term (months).


In the scheme of things, the Rb filter is narrower than the crystal is 
and these adjustments are very small compared to the Rb frequency (6 
GHz).  So setting the C-field to minimum and adjusting the final output 
frequency with the DDS to the closest step just below the desired 
frequency and then adjusting the C-field, by external comparison, to the 
correct wanted frequency achieves the desired result.


I know the calculator that comes with Windows XP will produce the 
correct mathematical results.  I think the Windows version 7 does the 
same.  I do not have Windows 10 and therefore cannot address that one, 
if there is one.  Even EXCEL spreadsheet does not do the job properly.  
So use caution with your calculations.


However, with all that said, it means nothing if you cannot properly 
measure the final value against an external standard of greater 
accuracy.  Acquiring the equipment to do the external measurements is 
where the real cost comes in.


At the minimum you will need a good “timing” GPSDO and I would highly 
recommend the Trimble Thunderbolt (properly set-up of course).  The next 
item is a good time interval counter like a HP 5335 with GPIB 
capability.  Add a GPIB controller to acquire the needed data, 
specifically one of these two 
https://www.sparkfun.com/search/results?term=gpib would be an excellent 
choice.  With these three items you can make a computer version of a 
strip chart measuring the delta difference in frequence between the 
Thunderbolt and the Rb.


Hopefully the above helps to clear up your query ?

BillWB6BNQ

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Re: [time-nuts] FE-5650A option 58 tuning word for 10 MHz output

[Attila Kinali]

Hoi Mathias!

On Tue, 03 Jan 2017 17:55:32 +0100
Mathias Weyland  wrote:

> On 2017-01-02 12:18, Attila Kinali wrote:

> > May I ask what you want to achieve? Resp. what you need a 10MHz
> > reference for?
> 
> I've always been wondering about those devices, I guess out of pure
> curiosity. Once I learned that those were available for cheap I knew
> I had to get one. But there is a secondary goal, which is to have
> a standard around to check my other gear against every now and then.
> Lately, I've been building and repairing 1.3 GHz radios and lost
> some time because I did not realize how much off both of my service
> monitors where. I could get away with a properly calibrated OCXO
> but the Rb was so much more sexy. So for the most part I need the
> 10 MHz for my own entertainment. :-)

So it's the usual curiosity and the need to have a reference for
your 23cm radios? For the latter I would recommend using a GPSDO
like the Trimble Thunderbolt or the Jacksonlabs Fury. There are also
a few Trimble OEM GPSDOs on ebay, but I have very little knowledge
about those. Advantage of an GPSDO over an Rb is that you know it's
on frequency, while with an Rb it can be off without you knowing it,
if the electronics or the physics package is defect. Of course, the
disadvantages are that most GPSDOs are made for fixed positions and
need a couple of hours of operation to achieve their nominal accuracy.
The short/mid-term stability (between 10s and ~1000s) is also slightly
worse than compared to an Rb.

To get the best of both worlds, there are a couple of GPSD-Rb around,
but commercial ones are usually quite expensive and modifying regular
GPSDOs to Rb is not always possible (at the very least you need to change
the control loop amplification).

BTW: there is a whole new way of looking at statistics of time series
in the field of time and frequency control, which you might find interesting.
The NIST Technote 1337[1] and NIST special publication 1065[2] give a nice
overview of the methods applied.

> > In general I would agree with Bill Houlne's comment that it's 
> > probably
> > easier to use a different reference that already has a 10MHz output.
> > Also keep in mind, that an output that has been designed as an PPS 
> > output
> > might not work as well as an output for 10MHz.
> 
> Yes I agree with that, but I'd also say that based on the reading I
> have done, it would be foolish to assume to get something that is
> guaranteed to work anyway. With all the things that could go wrong in
> general (dead unit, worn-out discharge lamp, drifted sweeping 
> boundaries
> of the oscillator etc.), the 1 pps to 10 MHz conversion for this 
> particular
> model(!) seems fairly straight forward. 

Most of the units sold on ebay work fairly well. And even a worn out
discharge lamp can often be recovered using a hot air gun.

> On the output issue you are rising: This particular model has a DDS 
> that
> takes a 50ish MHz reference and synthesizes another frequency which is
> a power of 2. A coax cable is taking that to a divider board where it's
> brought down to 1 Hz. This is all happening outside of the physics
> package. The plan is to reconfigure the DDS to synthesize 10 MHz 
> instead and bring out that coax. 

Ah..ok. That should work then.

> I would have to open a hole on the face plate
> to do that, but I'm fairly confident that this outer enclosure does not
> contribute to the actual magnetic shielding of the chamber... All
> modifications are strictly outside of the physics package (i.e. no
> water jet cutting...)

Unfortunately, it's not that easy :-)
I don't know the exact construction of the FE-5650, but usually the physics
package is just a normal aluminium microwave cavity, without shielding.
The mu-metal shield is usually the housing of the whole device itself.
Why this kind of construction is usually employed I do not know, but it
makes any modification of the case cumbersome. Mu-metal itself is quite
sensitive to shock and vibration and will lose (part of) its permeability
when being machined. You can of course try to drill as slowly as possible
to keep the heat and vibration at a minimum, but I have no idea how well
this works and I do not have any hard numbers on the sensitivity of
mu-metal either.

Attila Kinali

[1] "Characterization of Clocks and Oscillators", NIST Technote 1337,
by Sullivan, Allan, Howe, Walls, 1990
http://tf.nist.gov/general/pdf/868.pdf

[2] "Handbook of Frequency Stability Analysis" NIST Special Pub 1065,
by W.J. Riley, 2008
http://tf.nist.gov/timefreq/general/pdf/2220.pdf

-- 
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the prosperity and technological sophistication in the world is of no 
use without that foundation.
 -- Miss Matheson, The Diamond Age, Neil Stephenson
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Re: [time-nuts] FE-5650A option 58 tuning word for 10 MHz output

[Mathias Weyland]

On 2017-01-02 12:18, Attila Kinali wrote:

Attila!

Nice to see you around here ond au der es guez nois!



May I ask what you want to achieve? Resp. what you need a 10MHz
reference for?


I've always been wondering about those devices, I guess out of pure
curiosity. Once I learned that those were available for cheap I knew
I had to get one. But there is a secondary goal, which is to have
a standard around to check my other gear against every now and then.
Lately, I've been building and repairing 1.3 GHz radios and lost
some time because I did not realize how much off both of my service
monitors where. I could get away with a properly calibrated OCXO
but the Rb was so much more sexy. So for the most part I need the
10 MHz for my own entertainment. :-)


In general I would agree with Bill Houlne's comment that it's 
probably

easier to use a different reference that already has a 10MHz output.
Also keep in mind, that an output that has been designed as an PPS 
output

might not work as well as an output for 10MHz.


Yes I agree with that, but I'd also say that based on the reading I
have done, it would be foolish to assume to get something that is
guaranteed to work anyway. With all the things that could go wrong in
general (dead unit, worn-out discharge lamp, drifted sweeping 
boundaries
of the oscillator etc.), the 1 pps to 10 MHz conversion for this 
particular
model(!) seems fairly straight forward. In fact the only issue I've 
been

facing so far is the one that I'm trying to resolve in this thread. And
even if this cannot be resolved, the converted unit is still suitable 
for

my application.

On the output issue you are rising: This particular model has a DDS 
that

takes a 50ish MHz reference and synthesizes another frequency which is
a power of 2. A coax cable is taking that to a divider board where it's
brought down to 1 Hz. This is all happening outside of the physics
package. The plan is to reconfigure the DDS to synthesize 10 MHz 
instead

and bring out that coax. I would have to open a hole on the face plate
to do that, but I'm fairly confident that this outer enclosure does not
contribute to the actual magnetic shielding of the chamber... All
modifications are strictly outside of the physics package (i.e. no
water jet cutting...)


I am not master of desaster on this list, but it's usually ok to 
offer

this kind of stuff, as long as it is time-nut related.


OK thank you and hope to meet you soon!

Matt
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Re: [time-nuts] FE-5650A option 58 tuning word for 10 MHz output

[Alexander Pummer]

and if you glue a piece of non-magnetic material -- which could hold 
that connector -- it could be even some plastic, to the surface of the  
mu-metal , you do not need to worry about disturbing the magnetic conditions


73

KJ6UHN Alex


On 1/2/2017 3:44 PM, Attila Kinali wrote:

On Tue, 03 Jan 2017 11:02:54 +1300
Bruce Griffiths  wrote:


Maybe a waterjet cutter would  imapct less on the shielding properties of
tthe mumetal?

I doubt it. mu-metal is pretty sensitive to vibration as well and a
waterjet creates plenty of that. But anealing mu-metal is pretty simple,
if one has enough space to build a furnace in the backyard. All you have
to do is find a wall material that can withstand the 1000-1500°C annealing
temperature and which can be flooded with hydrogen is enough.

Flooding the furnace with hydrogen is not dangerous, as long as the
interior is completely flooded (no oxygen) and the hydrogen leaks
out at well controlled points, where it can burn off. There are
descriptions how to do that out there. The only problem is that you need
enough space around the furnace for the hydrogen flames to not cause any
trouble. Being outside also helps to prevent hydrogen build-ups on the
ceiling while initially flooding the furnace or shuting it off.


Attila Kinali


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Re: [time-nuts] FE-5650A option 58 tuning word for 10 MHz output

[Attila Kinali]

On Tue, 03 Jan 2017 11:02:54 +1300
Bruce Griffiths  wrote:

> Maybe a waterjet cutter would  imapct less on the shielding properties of 
> tthe mumetal?

I doubt it. mu-metal is pretty sensitive to vibration as well and a
waterjet creates plenty of that. But anealing mu-metal is pretty simple,
if one has enough space to build a furnace in the backyard. All you have
to do is find a wall material that can withstand the 1000-1500°C annealing
temperature and which can be flooded with hydrogen is enough.

Flooding the furnace with hydrogen is not dangerous, as long as the
interior is completely flooded (no oxygen) and the hydrogen leaks
out at well controlled points, where it can burn off. There are 
descriptions how to do that out there. The only problem is that you need
enough space around the furnace for the hydrogen flames to not cause any
trouble. Being outside also helps to prevent hydrogen build-ups on the
ceiling while initially flooding the furnace or shuting it off.


Attila Kinali
-- 
It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
 -- Miss Matheson, The Diamond Age, Neil Stephenson
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Re: [time-nuts] FE-5650A option 58 tuning word for 10 MHz output

[Bob Camp]

Hi

My biggest concern is that they magnetize the shield as they drill it. It’s a 
“static” field, but
it’s a static *near* field. I doubt that is a good thing ….

Bob

> On Jan 2, 2017, at 5:53 PM, Bruce Griffiths  
> wrote:
> 
> One could always wrap the assembly with its impaired mu metal shield in 
> several layers of flexible magnetic shielding foil to regain the desired 
> magnetic shielding e.Most such foils can be cut with scissors without 
> significant effect on their magnetic properties. 
> Bruce
> 
>On Tuesday, 3 January 2017 11:46 AM, Bob Camp  wrote:
> 
> 
> Hi
> 
> 
>> On Jan 2, 2017, at 5:02 PM, Bruce Griffiths  
>> wrote:
>> 
>> 
>> Maybe a waterjet cutter would  imapct less on the shielding properties of 
>> tthe mumetal?
>> 
> 
> Maybe …. pretty good bet that the guys modifying these in their living room 
> aren’t focused on much more than getting them working as fast as they possibly
> can. 
> 
> Bob
> 
>> Bruce
>> 
>> On Monday, January 02, 2017 12:58:55 PM Bob Camp wrote:
>>> Hi
>>> 
 On Jan 1, 2017, at 7:31 PM, wb6bnq  wrote:
 
 Hello Mathias,
 
 I think you did not quite understand how the calibration process works
 with that unit.  The factory procedure is to set the pot to minimum and
 then bring the DDS up to the step that produces the closest 
> 
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> 
> 
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Re: [time-nuts] FE-5650A option 58 tuning word for 10 MHz output

[Bruce Griffiths]

One could always wrap the assembly with its impaired mu metal shield in several 
layers of flexible magnetic shielding foil to regain the desired magnetic 
shielding e.Most such foils can be cut with scissors without significant effect 
on their magnetic properties. 
Bruce

On Tuesday, 3 January 2017 11:46 AM, Bob Camp  wrote:
 

 Hi


> On Jan 2, 2017, at 5:02 PM, Bruce Griffiths  
> wrote:
> 
> 
> Maybe a waterjet cutter would  imapct less on the shielding properties of 
> tthe mumetal?
> 

Maybe …. pretty good bet that the guys modifying these in their living room 
aren’t focused on much more than getting them working as fast as they possibly
can. 

Bob

> Bruce
> 
> On Monday, January 02, 2017 12:58:55 PM Bob Camp wrote:
>> Hi
>> 
>>> On Jan 1, 2017, at 7:31 PM, wb6bnq  wrote:
>>> 
>>> Hello Mathias,
>>> 
>>> I think you did not quite understand how the calibration process works
>>> with that unit.  The factory procedure is to set the pot to minimum and
>>> then bring the DDS up to the step that produces the closest 

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Re: [time-nuts] FE-5650A option 58 tuning word for 10 MHz output

[Bob Camp]

Hi


> On Jan 2, 2017, at 5:02 PM, Bruce Griffiths  
> wrote:
> 
> 
> Maybe a waterjet cutter would  imapct less on the shielding properties of 
> tthe mumetal?
> 

Maybe …. pretty good bet that the guys modifying these in their living room 
aren’t focused on much more than getting them working as fast as they possibly
can. 

Bob

> Bruce
> 
> On Monday, January 02, 2017 12:58:55 PM Bob Camp wrote:
>> Hi
>> 
>>> On Jan 1, 2017, at 7:31 PM, wb6bnq  wrote:
>>> 
>>> Hello Mathias,
>>> 
>>> I think you did not quite understand how the calibration process works
>>> with that unit.  The factory procedure is to set the pot to minimum and
>>> then bring the DDS up to the step that produces the closest 

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Re: [time-nuts] FE-5650A option 58 tuning word for 10 MHz output

[Bruce Griffiths]

Maybe a waterjet cutter would  imapct less on the shielding properties of 
tthe mumetal?

Bruce

On Monday, January 02, 2017 12:58:55 PM Bob Camp wrote:
> Hi
> 
> > On Jan 1, 2017, at 7:31 PM, wb6bnq  wrote:
> > 
> > Hello Mathias,
> > 
> > I think you did not quite understand how the calibration process works
> > with that unit.  The factory procedure is to set the pot to minimum and
> > then bring the DDS up to the step that produces the closest 
frequency
> > just below the wanted one and then use the C-field pot as the final
> > tweak.
> > 
> > The "R" value is composed of a number of factors that can only be
> > determined after the Rb cell is made.  A number of variables, in the Rb
> > cell itself, will determine the actual "ON" resonance frequency and that
> > is what is programmed into the "R" number at the end of final 
assembly.
> > 
> > That "R" number is actually the Rb frequency divided by 136 plus the
> > upward fine tuning of the C-field pot.  See PDF page 16 & 17 of the
> > attached PDF operational manual for the FEI-5650.  The only 
difference
> > between all the variants comes after the Physics Package as shown 
on PDF
> > page 16 block diagram.
> > 
> > The "F" number is truly a 32 bit number, not just the first 8 digits but
> > all 16 of them.
> > 
> > Your problem is being able to have a frequency reference that is,
> > obviously, way better then the Rb.  As Cesium and Hydrogen 
references are
> > quite expensive that leaves just the GPS satellites as the only other
> > reference available that will do the job.  Of course that entails more
> > than just the GPS "timing" receiver as you will need some other 
equipment
> > to help in the comparison process.  Also it takes time to do many 
small
> > adjustments to achieve that final comparison.  It won't happen in just
> > one day.
> > 
> > It would probably have been better to purchase one of the Rb's that
> > already output 10 MHz instead of hacking the option 58.  BUT that is 
just
> > my opinion.
> This heads you down another rabbit hole. Since the 10 MHz output units 
sell
> better than the PPS only versions, there is a cottage industry going to
> convert one to the other. Parts are missing on the board to make a 
“proper”
> 10 MHz unit. The conversion often is a bit ugly. No matter how well it is
> done electrically, bashing a hole in the magnetic shield case for the SMA
> is a really bad idea unless you have the proper gear to heat create it
> after you are done.
> 
> So yes, the 10 MHz version is a better way to go, but only if it came from
> the factory as a 10 MHz unit …..
> 
> Bob
> 
> > Good luck,
> > 
> > Bill HoulneWB6BNQ
> > 
> > Mathias Weyland wrote:
> >> Hello guys
> >> 
> >> I'm new to this list. I got myself a FE-5650A Rubidium Standard off of
> >> ebay. It's the "option 58" 1 pps output variant, hence I have to 
modify
> >> the tuning word used in the DDS phase accumulator to get 10 MHz 
out. I
> >> found a vast amount of awesome descriptions on how to do that on 
the web
> >> and in particular on this list. One write-up that stood out was this 
one
> >> by Mark Sims:
> >> 
> >> http://www.mail-archive.com/time-nuts@febo.com/msg13486.html
> >> 
> >> I think I can pull this off since everything is documented so nicely.
> >> However, I'm having trouble calculating the right tuning word and 
this
> >> is why: Mark notes that the reference frequency reported by the unit 
is
> >> the one with the C-field pot at the lowest frequency position. He 
gives
> >> a number of suggestions on how to deal with that. Since I didn't get
> >> that hydrogen maser for Christmas, the best approach seems to be 
"to
> >> calculate the true reference frequency from the saved (minimum C-
field)
> >> R=reference frequency and F=divisor word and use that value to 
calculate
> >> divisor words." I don't understand how the saved minimum C-field
> >> reference ties into this calculation.
> >> 
> >> My approach would have been to calculate the true reference 
frequency
> >> from the saved divisor alone, ignoring the minimum C-field 
calculation.
> >> I don't see how the minimum C-field reference frequency would help 
me
> >> since the C-field pot is not in the min position anymore due to 
factory
> >> tweaking. To be specific, this is what I would do:
> >> 
> >> The unit returns the following string upon 'S':
> >> 
> >> OK50255055.760840Hz F=2ABB5046B34A2E00
> >> 
> >> Now based on this, the tuning word should be coded in the first 8
> >> characters, of F, i.e. '2ABB5046'. I'm a bit confused about the
> >> remaining characters being non-zero. Any documentation I came 
across has
> >> a number that ends in 8 zeroes... In any case, 0x2ABB5046 is 
716918854
> >> in decimal and the resolution would therefore be
> >> 
> >> 2^23 / 716918854 = approx. 0.0117 Hz which makes sense.
> >> 
> >> The physics package would then output a frequency of
> >> 
> >> f_ref = (2^23 / 716918854) * 2^32 = approx. 50255055.809934 Hz
> >> 
> >> This is 

Re: [time-nuts] FE-5650A option 58 tuning word for 10 MHz output

[Bob Camp]

Hi




> On Jan 1, 2017, at 7:31 PM, wb6bnq  wrote:
> 
> Hello Mathias,
> 
> I think you did not quite understand how the calibration process works with 
> that unit.  The factory procedure is to set the pot to minimum and then bring 
> the DDS up to the step that produces the closest frequency just below the 
> wanted one and then use the C-field pot as the final tweak.
> 
> The "R" value is composed of a number of factors that can only be determined 
> after the Rb cell is made.  A number of variables, in the Rb cell itself, 
> will determine the actual "ON" resonance frequency and that is what is 
> programmed into the "R" number at the end of final assembly.
> 
> That "R" number is actually the Rb frequency divided by 136 plus the upward 
> fine tuning of the C-field pot.  See PDF page 16 & 17 of the attached PDF 
> operational manual for the FEI-5650.  The only difference between all the 
> variants comes after the Physics Package as shown on PDF page 16 block 
> diagram.
> 
> The "F" number is truly a 32 bit number, not just the first 8 digits but all 
> 16 of them.
> 
> Your problem is being able to have a frequency reference that is, obviously, 
> way better then the Rb.  As Cesium and Hydrogen references are quite 
> expensive that leaves just the GPS satellites as the only other reference 
> available that will do the job.  Of course that entails more than just the 
> GPS "timing" receiver as you will need some other equipment to help in the 
> comparison process.  Also it takes time to do many small adjustments to 
> achieve that final comparison.  It won't happen in just one day.
> 
> It would probably have been better to purchase one of the Rb's that already 
> output 10 MHz instead of hacking the option 58.  BUT that is just my opinion.
> 

This heads you down another rabbit hole. Since the 10 MHz output units sell 
better than the PPS only versions, there is a cottage industry going to convert
one to the other. Parts are missing on the board to make a “proper” 10 MHz 
unit. The conversion often is a bit ugly. No matter how well it is done
electrically, bashing a hole in the magnetic shield case for the SMA is a 
really bad idea unless you have the proper gear to heat create it after you are 
done. 

So yes, the 10 MHz version is a better way to go, but only if it came from the 
factory as a 10 MHz unit …..

Bob



> Good luck,
> 
> Bill HoulneWB6BNQ
> 
> Mathias Weyland wrote:
> 
>> Hello guys
>> 
>> I'm new to this list. I got myself a FE-5650A Rubidium Standard off of ebay.
>> It's the "option 58" 1 pps output variant, hence I have to modify the tuning
>> word used in the DDS phase accumulator to get 10 MHz out. I found a vast 
>> amount
>> of awesome descriptions on how to do that on the web and in particular on 
>> this
>> list. One write-up that stood out was this one by Mark Sims:
>> 
>> http://www.mail-archive.com/time-nuts@febo.com/msg13486.html
>> 
>> I think I can pull this off since everything is documented so nicely. 
>> However,
>> I'm having trouble calculating the right tuning word and this is why: Mark 
>> notes
>> that the reference frequency reported by the unit is the one with the C-field
>> pot at the lowest frequency position. He gives a number of suggestions on 
>> how to
>> deal with that. Since I didn't get that hydrogen maser for Christmas, the 
>> best
>> approach seems to be "to calculate the true reference frequency from the 
>> saved
>> (minimum C-field) R=reference frequency and F=divisor word and use that 
>> value to
>> calculate divisor words." I don't understand how the saved minimum C-field
>> reference ties into this calculation.
>> 
>> My approach would have been to calculate the true reference frequency from 
>> the
>> saved divisor alone, ignoring the minimum C-field calculation. I don't see 
>> how
>> the minimum C-field reference frequency would help me since the C-field pot 
>> is
>> not in the min position anymore due to factory tweaking. To be specific, 
>> this is
>> what I would do:
>> 
>> The unit returns the following string upon 'S':
>> 
>> OK50255055.760840Hz F=2ABB5046B34A2E00
>> 
>> Now based on this, the tuning word should be coded in the first 8 
>> characters, of
>> F, i.e. '2ABB5046'. I'm a bit confused about the remaining characters being
>> non-zero. Any documentation I came across has a number that ends in 8 
>> zeroes...
>> In any case, 0x2ABB5046 is 716918854 in decimal and the resolution would
>> therefore be
>> 
>> 2^23 / 716918854 = approx. 0.0117 Hz which makes sense.
>> 
>> The physics package would then output a frequency of
>> 
>> f_ref = (2^23 / 716918854) * 2^32 = approx. 50255055.809934 Hz
>> 
>> This is higher than the reference given in the 'S' output, which is in line 
>> with
>> what Mark wrote. However, scaling this with the average correction factor he
>> gave yields
>> 
>> f_ref * 1.2150 = approx. 50255055.917982 Hz
>> 
>> Which is higher than what I would expect. Then again I'm not 

Re: [time-nuts] FE-5650A option 58 tuning word for 10 MHz output

[Mathias Weyland]

On 2017-01-02 01:31, wb6bnq wrote:

Hello Bill

Thanks for your response and the pdf manual. There's lots of good
information in there. You are certainly right in that there's a
few things that I have not understood. Unfortunately this has not
changed after having read your response:



 That "R" number is actually the Rb frequency divided by 136 plus the
upward fine tuning of the C-field pot.  See PDF page 16 & 17 of the
attached PDF operational manual for the FEI-5650.


In the comprehensive post[*] that I quote in my original request,
Mark states that "THE R= REFERENCE FREQUENCY IS NOT THE FREQUENCY
THAT THE  PHYSICS PACKAGE IS SHIPPED TUNED TO!!!  It is the
frequency produced by the  physics package at the minimum setting
of the C-field potentiometer."

This seems to be contradictory to what you wrote. Either the R value
is determined at the C-field pot minimum frequency position as Mark
stated, in which case it does not contain the upward C-field
tweaking. Or it is determined after the final tweaking as you say.
Either way I don't understand how to incorporate the R reference
frequency into my calculations, which is what Mark seems to be
suggesting.



 The "F" number is truly a 32 bit number, not just the first 8 digits
but all 16 of them.


The F number has 16 hex digits. Since each of those digits represents
a nibble (i.e. half a byte, 4 bits), I end up with 16*4 = 64 bits. Not
just 32. The first 8 digits of the F number however represent a 32 bit
number, which is also the size of the the phase accumulator in the
AD9830 which makes sense in my opinion. I think I absolutely failed
to grasp what you're trying to tell me here :-(

Re-reading the paragraph in [*] that starts with "You can set the
divisor" did clear up something for me though -- looks like there's
nothing weird with the F-number stored in my unit; the last byte is
indeed 0x00. I still don't quite understand why this parameter is
potentially stored at a higher precision than what the DDS can
deliver.



 It would probably have been better to purchase one of the Rb's that
already output 10 MHz instead of hacking the option 58.  BUT that is
just my opinion.


You are probably right on that, yet getting any of those surplus
standards off of ebay seems to be a bit of a hit-or-miss thing
anyway. At least I get the learning experience, that's gotta count
for something :-).

Thanks again for your response and best regards

Matt
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Re: [time-nuts] FE-5650A option 58 tuning word for 10 MHz output

[Attila Kinali]

Hoi Mathias!

Wie goht's wie stoht's? :-)

On Sat, 31 Dec 2016 15:33:53 +0100
Mathias Weyland  wrote:

> I'm new to this list. I got myself a FE-5650A Rubidium Standard off of 
> ebay.
> It's the "option 58" 1 pps output variant, hence I have to modify the 
> tuning
> word used in the DDS phase accumulator to get 10 MHz out.

May I ask what you want to achieve? Resp. what you need a 10MHz reference for?

In general I would agree with Bill Houlne's comment that it's probably
easier to use a different reference that already has a 10MHz output.
Also keep in mind, that an output that has been designed as an PPS output
might not work as well as an output for 10MHz.

> On a slightly related note, I have cooked up a small PCB with a local 5V
> regulator and status LEDs that mates with the amphenol connector used on this
> standard. I have to complete the write-up on it and will probably put up a
> video about the mod on my youtube channel; once this is done I'll be sitting 
> on
> 9 spare boards since I got 10 boards done. If there is interest, I could send
> off the spares without profit, i.e. for about 5 bucks or so. I imagine this
> could be of use to those who have the same standard. The board doesn't do
> anything funky, it is just neat. In any case I'd like to ask if it would be OK
> to formally place this offer on the list once I got everything ready.

I am not master of desaster on this list, but it's usually ok to offer
this kind of stuff, as long as it is time-nut related.

Gruess und guets neus!

Attila Kinali

-- 
It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
 -- Miss Matheson, The Diamond Age, Neil Stephenson
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