[time-nuts] E-5680A C-field trimer ??

Mark Sims holrum at hotmail.com
Mon Aug 25 18:25:55 EDT 2008

Actually the 5680A and 5650A units that have the DDS do have a C-field pot.  The DDS is only accurate to 0.01 Hz.  They set the C-field to minimum,  program the DDS constant that gets the closest to the desired freq into the CPU chip (this is what gets reported by the "S" command),  then they tweak the C-field to get the unit exactly on freq.  The reference freq reported by the "S" command is NOT the reference freq that the unit is shipped adjusted to.

>There are several models of the 5680A.  A lot use the DDS circuits to
>set the output frequencies and  they do not have C field adjustments.

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