G3VPX HF Transceiver - AD9854 DDS PCB design

The Analog devices AD9854 DDS chips were mounted on small carrier boards as shown in the photos.

The layout below is a top view. Double click to download a high-resolution BMP version.


This is a top view so you must mirror - print this image onto the laser film.

The above layout has separate Analog and digital ground sections. The underside of the board is a ground plane and was correspondingly split into two.

Note the my 1st local oscillator DDS didn't have the analog and digital grounds separated ... but the CIO did - this is simply historical - the LO DDS board was made in August 2005.... I've learned a bit since then!. They should be split !

The local oscillator is clocked at 200Mhz ... this needs the 'SQ' version of the chip with a metal heat pad underneath. Hence the square hole under the board. My board rests on a filed down square steel bolt-head (with heat transfer compund) to use the aluminium tray a big heat sink.

The hole is also very useful for soldering the chip. My procedure is: Tin the board. Clean it up with desolder wick (use flux ... dont rip off the copper track with the wick). Postion the chip fixing it with blue-tack under the hole ... using a magnifying glass. Quickly flood solder each side (this shorts many of the pins). Then remove the exceess sodler with desoldering wick. Then check for shorted pins or unsoldered pins both with a magnifying glass and low voltage test meter.