[Amps] Low Pass Filter capacitor failures

[peter chadwick]

Rogers 'Duroid' Teflon PCB material is very good for making suitable capacitors, and you can actually calculate quite easily the size and loss. It has an advantage over sheet Teflon and aluminium that there aren't any airgaps and it doesn't need clamping together, which can lead to 'creep' of the Teflon. At 2 metres, the skin depth is 0.00022 inch and so 1 ounce copper will be about 6.5 skin depths, which should be adequate: 2 ounce copper might offer a measurable improvement, but I doubt it. The only point to watch then is the expected current density in the metal and the loss in the dielectric, which you can calculate from the loss tangent.

Spice will give you answers on voltages and currents, but if you don't have Spice, it's not that hard to calculate, especially with a programmable calculator, let alone a computer.

Jim said the band is 144 to 148 MHz: not in ITU Region 1. Where the OP lives, it is 144 to 146MHz. One needs to define what is meant by cut off frequency, too.

73

Peter G3RZP