Wednesday, August 20, 2014

Revisiting DC blocking solutions for DC damaged IF filters

During these last years a new problem appeared in many commercial ham radio equipment, from many manufacturers. The receivers suddenly become deaf, hearing only really strong signals. The problem is the premature failure of IF filters, because DC is applied to them. Why?

Because applying DC to these piezoelectric devices causes electromigration, and therefore the filter destruction. Manufacturers warns about applying DC to the filters, but manufacturers have been ignoring this for decades.

A transceiver with this problem can be easily repaired by just replacing all the damaged filters, and to prevent this problem to appear again, a pair of DC blocking capacitors must be inserted at the filter input/output pins. In fact some manufacturers have modified their PCB in latest revisions to add these capacitors. But are these capacitors enough to keep DC out of the filters?

Tuesday, August 19, 2014

Simple phone battery test

Do you suspect from your phone battery? Testing today's mobile batteries is very easy: Lay it over a flat surface and make it to spin.