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

wb6bnq wb6bnq at cox.net
Tue Jan 10 04:07:45 EST 2017


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.

Bill....WB6BNQ


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" <wb6bnq at cox.net> 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.
>>
>>Bill....WB6BNQ
>>
>>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 <scott.j.stobbe at gmail.com>
>>>>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 <wb6bnq at cox.net> wrote:
>>>>
>>>>
>>>>
>>>>        
>>>>
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>>>      
>>>
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