Paul, NPO is an old acronym for "negative positive zero", for ceramic capacitors that have a nearly-constant dielectric constant (K, also known as permittivity). The temperature coefficient for the capacitance is approximately 0 parts-per-million per degree C over the specified operating temperature range for the capacitor. If you are designing a critical inductor-capacitor (LC) tuned-circuit, you may want to compensate for the (usually) positive temperature coefficient of the inductor. By parallelling two ceramic capacitors, one with a specified negative temperature coefficient, and one with an NPO/C0G temperature coefficient, you can vary the ratio of their values to get just about any nominal value and negative temperature coefficient that you may need. Doug DeMaw's ham-radio books talk about this scheme in a lot more detail. John Barnes KS4GL dBi Corporation http://www.dbicorporation.com/ ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu