Sunday, December 22, 2013

B Board synthesizer construction

The first B board was populated incrementally.  Previous experience had shown the QFN32 (or similar) packages to be challenging to properly solder, at least for me.  To help with this in the layout the center pads were shrunk to avoid shorts with the outer pads, and the outer pads extended out significantly.  The pad extension has several effects: a) it provides a better overall visual alignment queue, b) it provides a reservoir for solder, c) it provides additional re-work and alignment space.  While this will impact device performance, the apparent alternative is to not use the part or pay to have boards populated (both of which defeat the point of the exercise).  

Below is a picture of the synthesizer portion populated (along with the DFN8 mixer which air gunned at the same time as the ADF4351 and TCXO).  It is mounted on a previous build A board (ADC IF) which in turn mounts on a Beagle Bone Black.
The ADF4351 (U104) is left center just to the right of the TCXO. 

Beagle Bone C/C++ software using the GPIO sysfs interface was developed to configure and monitor the devices including lock detect indicator.  The following are spectra of the aux output using lowest power level at 100, 300, 500, 700, and 900MHz.  The display is from a 7L12 (1973 vintage, user calibrated - I'm on a budget).


100MHz Aux Output


300MHz Aux Output

500MHz Aux Output
700MHz Aux Output
900MHz Aux Output
The 7L12 limit is 1500MHz and the output is similarly clean to that limit.  Below is the schematic of the board as ordered and built thus far.

131212 B Board As-Ordered Schematic



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