Peter, Excessive energy applied to the capacitors is the most likely culprit. Any of the following might be the cause:
1) Excessive power supply ripple. Especially with tantalum capacitors, this will exceed the voltage rating even though the apparent DC level measured with a meter appears to be within specification. The voltage rating is somewhat misleading in many applications. It is a DC rating based on typical usage. The Effective Series Resistance (ESR) of the capacitor determines its power handling capability at a particular frequency. This is determined by performing a reactance plot of the component. Many manufacturers are somewhat "cagey" with published specifications, and seemingly identical components will not perform the same. 2) Lightning or Electrostatic Discharge. Either one of these will raise havoc with internal components. That outside antenna should have a properly earthed protection device at the point where it enters the building. The earth at the antenna protective device must have a solid (copper) connection to the power line earth at the service entry or it may aggravate the problem. Soil alone is not a sufficient connection. 3) Unintentional RF pickup at the antenna. High powered mobile transmitters can and will cause RF burns to components in some instances. Sites where explosives are in use ban operation of mobile transmitters for this reason. RF energy sufficient to ignite a detonator will easily destroy smaller capacitors. Scott Lacey sla...@foxboro.com --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to ed.pr...@cubic.com, j...@gwmail.monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators).
