Friday, November 7, 2014

Looking inside a 144 - 432 - 1296 triplexer

It has recently come into my hands a 144 - 432 - 1296 MHz triplexer. A Comet CFX-4310. I was curious, so I opened it:

The construction is quite classic, without fancy components. It is interesting that the 23cm arm is build using trimmers, and every other capacitor is made from two capacitors in parallel. It was so clear that I drew the schematic, just to keep it:

CFX-4310 schematic

Component values are:

C1: Trimmer
C9: 3pF
C17: 8pF
L4: 2 turns
C2: Trimmer
C10: 3pF
C18: 15pF
L5: 1 turn
C3: Trimmer
C11: 2pF
C19: 11pF
L6: 2 turns
C4: Trimmer
C12: 3pF
C20: 3pF
L7: 2 turns
C5: Trimmer
C13: 3pF
C21: 3pF
L8: 2 turns
C6: 2pF
C14: 10pF
L1: See text
L9: 5 turns
C7: 2pF
C15: 5pF
L2: 2 turns
L10: 4 turns
C8: 2pF
C16: 8pF
L3: 2 turns

Some quick notes:

  • All capacitors seems to be 500 volts rated.
  • All coils are 5mm internal diameter with 1mm diameter enamelled wire.
  • All coils seem to be "tuned" by adjusting turn separation.
  • L4 and L5 are placed together, so I suspect they are coupled.
  • L1 is made with a small piece of cooper sheet in "M" shape.
  • C1-C5 are small ceramic trimmers, maybe 10-15pF maximum.
  • L2-C5 is a tuned trap I suspect is tuned to 435 MHz.

And that's all. So in the case you burn one capacitor you can replace it using the above table.

Miguel A. Vallejo, EA4EOZ


  1. Hello,
    thank you for this post and others (especially the noise source mod!).
    Could you please check: you wrote that in 23cm part every capacitor is made of two in parallel, but on the schematic they are connected in series. Which one is correct?

    1. The schematic is correct. Just look carefully the photo. I changed that phrase to avoid further confusion.