Another one from the archives :o). This is a design for a low pass filter for 29 MHz and would be suitable for anyone on the 28 MHz or 27 MHz bands who needs a filter to reduce harmonics. This is especially valid for anyone using a low powered radio to drive an external amplifier. e.g. Amplifying 4w to say 50-100w.
Coils...12 SWG wire. 6 turns. 8mm internal diameter. Coil length 19mm.
Capacitors...High Voltage ceramic or Mica. 110pf Cap is 100pf and 10pf in parallel.
A suitable enclosure might be a diecast box with the filter built on copper clad board. Note the screen which can be made from the pcb material as well. If you can live with a slightly lower performance in terms of filtering, you can omit the internal screens but make sure you put it in a metal box.