Low pass filters

Richard G4TGJ

A number of people have had problems with the power output of their QCX and the solution has often been to remove a turn or two from L1-L3. I have been working on my own transceiver and I have been using the W3NQN CWAZ LPF designs from the GQRP Club datasheet. I've been analysing the 20m LPF with my nanoVNA and have had to remove 2 turns from L2 and L6 and 1 turn from L4 to get a satisfactory passband return loss and insertion loss. That's a change in inductance way beyond the 5% tolerance of AL or the 5% capacitance tolerance. Has anybody else done similar tests? Is there a widespread problem with the toroids? Mine came from GQRP Club Sales so I assume they are Micrometals.

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