AD8307 RF Power Meter III — build

This will be another short post. I also made the GitHub repo public, but please be aware, current design is flawed. If you use it, you acknowledge that you use it on your own risk.

Today I managed to build the revision 1.0 of this power sensor, not without some lessons learned. It was my first attempt at working with SMD components.

Overall not bad, given it was my first ever experience with a hot air station and 0603 SMD. The Gordak 952 was decent, but a bit too powerful. I had to turn the airflow all way down and use the gun perfectly perpendicular to the board, otherwise the smaller components were blown away. I am seriously considering buing an oven, something like this infrared IC heater. BTW, this Gordak seems to be branded for S-E Europe only. I could not find it on the web elsewhere. Probably a clone of a clone etc.

I also discovered a design error that highlights the importance of running a thorough ERC before any attempt to create the PCB. It seems that I completely forgot I need a DPST switch for coupling the input attenuator. The result: the input is not electrically connected with the main circuit so I must add two straps to connect each end of the switch with the corresponding circuit nodes. More about that in a future post.

Lessons learned:

  1. Prepare components/ place them nearby before applying the solder paste; it took a considerable amount of time to get each SMD component out of its bag, strip it from the tape, pick it with the tweezer and place it over its pads; for a small project this might not matter too much but for larger projects it might result in drying out the solder paste;
  2. Never, ever order the PCB fabrication before having all components; since KiCad libraries are not not very well integrated (yet) with all major vendors own component databases, it is always the risk to design with one type of component (footprint etc) and order the wrong one;

Will be back with operational tests.

Author: AP

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