Re: [Discuss-gnuradio] Need some answers about FM TX

[Robert McGwier]

Thanks for all the comments but I still have my doubts.  I am more like 
to believe in clock leakage and DAC nonlinearities causing this than I 
am with square wave harmonic activity.  I will investigate further with 
the spec-an if I have time.

The pico-board looks great. I recently acquired the AD9954 eval board 
(two 9954's sync'd for I/Q)  and a AD9958 eval board to learn what was 
going on.  AD is a serious believer these days in DAC nonlinearities and 
clock leakage causing all sorts of issues that are mistaken for other 
things and as such they are truly seriously pushing the 9958 with its 10 
bit DAC and smaller accumulator and phase word which seems so 
counterintuitive but as you all say, measurements will tell the tale.  
Their app engineers are all over you when you talk to them at length 
about the problems attributed to phase truncations which mathematically 
cannot be and which they have tracked down to DAC/clock leak issues.

I will post a note here with some results.

Bob




address@hidden wrote:

> The same does apply to a DAC as well as an ADC.  They are both sampling 
> systems.  A DAC typically has a low pass filter to cut all the alias 
> images.  But you can also bandpass filter those images to produce the 
> desired signal.  The system is very linear and isn't a mixer.
>
> Here is my original post:
>
>