Another though... The FE5680A manual says that the most basic unit
outputs 50.255+ MHz (1/136 the Rb oscillation frequency). I suppose that
this is the "other" style of units, that uses a 50.255MHz crystal to
excite the cavity. 50.255MHz/2^48 is 1.785416^-7Hz, the claimed
resolution for these FE-5680A.
I'm starting to suspect that the claimed resolution of 1.7854^-7Hz is
only for a serial protocol compatibility reason, and that really the
effective tuning step for these Rbs is in fact around 6.81^-6Hz.
Regards,
Javier, EA1CRB
El 28/01/2012 20:44, Javier Herrero escribió:
I've checked now that they do not seem to be any activity on the DDS
SPI lines during normal operation. I've tried with several small
offsets through the serial port, and the square wave at FSELECT seems
to be same square, no appreciable duty cycle variation.
Regards,
Javier
El 28/01/2012 20:32, ed breya escribió:
The lower bits can be pulse width modulated to get finer resolution,
but it gets harder to maintain monotonicity. Eventually you run out
of processing resolution, or the control signal falls into the noise
floor, whether the system is digital, analog, or both.
Ed
Javier Herrero wrote:
Sat Jan 28 18:38:53 UTC 2012
It can be... but the resolution of the center frequency of two DDS
frequencies would be limited to half DDS LSB... so not enough. I will
try to monitor FSELECT and also to extract some SPI data if I found some
free time today or tomorrow :)
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Chief Technology Officer EMAIL: [email protected]
HV Sistemas S.L. PHONE: +34 949 336 806
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