The filter is more or less a standard 7-pole filter for the 20m band. It is used in many designs. Found it on the net. Thank you mr ?? for putting it on the net. Make sure that you use correct cores. I used the T86-6 cores. Maybe a little bit over designed, but we will later on check the temperatures of the cores when in operation.

The capacitors should also be of a good quality and certainly capable of handling the high voltages. I would say 400 volts should be ok for a 50-100 Watt output. If not we will see it later on,.......poefhh,.....

In my first proto I will build the filter directly on the amp PCB, so we don't need the plugs. I will measure later on the pass filter characteristics separately on a bread board, before building it in the amp. I want to make sure that the cutoff frequency is higher than 14.350 MHz !

In the QCX kit I only got 1,5 watts of output, because the filter was to 'tight'. I measure the filter with a Marconi 2030 with 0 dB input and let the instrument go from 12MHz to 20 Mhz. After doing that I give the output curve in this document. Make sure the input is driven from a 50ohm signal generator and the output is terminated with 50 ohms !

That is all about the filter !