Topband: Mica capacitors for antenna matching.

[Tom Boucher]

There's been a thread on here about using silvered mica capacitors for antenna matching networks. I have had no success at all using these as they don't appear to handle any significant amount of current and usually disappear in a puff of smoke. For several years I have used 'L' matching networks for my 160M inverted 'L' which use high voltage disc ceramics sold by Farnell (Newark in US). These are rated at 6.3KV and have survived decent amounts of RF power without getting hot. Farnell/Newark part numbers are 952-7311 (220pF), 952-7303 (100pF), 952-7290 (47pF) and 952-7281 (22pF). Most capacitance values required can be made up by series/parallel arrangements of these.

Another issue regarding use of 'L' matching networks - it's better to use a low-pass arrangement (parallel capacitor to ground) from a harmonic rejection viewpoint rather than the high-pass configuration (inductor to ground), BUT the high pass offers better lightning protection.

73
Tom G3OLB