locked Re: FST$4W in a PIC #FST4W

Bill Somerville

On 16/03/2021 21:31, Andy TALBOT wrote:
The ramping in the AD9852 is a linear sweep.   That used for FST4 is Gaussian shaped  Having worked put how to do a proper shaped one, reverting to a linear ramp just because the chip can do it itself is a cop-out.  

The 9852 is rather long in the tooth now, may be worth looking for an improved DDS, although 48 bit ones are rarer.

Hi Andy,

non-linear ramping is well defined for that DDS, the ramp control can be changed and timed on the fly as I said before. Even if the ramp is divided into a few segments with different slopes it will probably be better than trying to tweak the DDS in single frequency mode at exactly the right intervals to generate anything like a Gaussian filter. In fact I suspect a linear ramped-FSK will be better than any attempt at a piecemeal generation a Gaussian filtered MFSK, certainly much easier to generate using the DDS chip's facilities for it.


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