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Re: Si5351a issues with frequency resolution (step size) at 144MHz (or even lower frequencies)

 

Ron,? I don't know if any links exist to the original Clockbuilder Desktop, but I have the installation .zip file and can send you a copy if you need one.? I've used it and the new Clockbuilder Pro. The desktop version seems easier to use, but the Pro version (once you figure it out) seems to provide more information. I have not used either one enough to be aware of their limitations.

It hasn't helped me so far. I can generate a set of bit values, which could then be assembled into bytes and uploaded to appropriate?registers, but I'm still struggling?with register names and sizes which don't always seem to correlate between the spec sheet and the Clockbuilder Pro output. No doubt it's my mistake and eventually I'll start to understand it better.

It would be nice if some code (Arduino/C++) existed that took the Clockbuilder Pro register bit calculation results, assembled them into bytes and uploaded them to the Si5351. I guess parts of the required?code must already exist as parts of the Arduino library.? I did make an attempt at using?si5351.set_freq_manual, using the VCO frequency that clockbuilder found and hoping that the librartycode would do the rest, It seemed to work for one frequency, but for another it generated a very ugly, very wide spread signal, so obviously there's more to it than what I tried. Still learning here, only been battling with it for about a week!? I'm using 64 bit integers (ULL) and appropriate(?) coding, but I'm still doing no better then getting within a couple of Hz of the desired frequency, with significant variation in step size when trying to make equal steps of a few Hz.

Bob, KA1GT

On Mon, Jan 23, 2023 at 12:35 PM Ron Carr <rcarr@...> wrote:
Bob,

It looks as though to generate signals in the 144mhz range, the Si5351 will be using a fixed output divider of 6.? A simple Si5351 library that uses fixed point and does nothing fancy but does allow fractional frequencies should have a 1/6 hz accuracy, in that the PLL frequency is calculated to the nearest hz using fixed point.? To get a one hz change at 144mhz the PLL will change by 6 hz.? ( divider is 6 ).? To do better would require calculating the PLL frequency to a fractional frequency.? The NT7S library uses the target frequency scaled up by 100 for fractional frequencies, but I didn't look to see if it was scaling up the PLL frequency also.? I also found two NT7S libraries, one under etherkit which I think is the one everyone uses and some older C code that is aimed at Arduino.? I wonder which you tried.

Ron? KE1MU

Does anyone know where to download the old version of clockbuilder?? The new Pro version is crippled and no longer allows assigning PLL's to outputs or allows integer output dividers.

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