Unilab 10m FM conversion Transmitter PA mods - Low Pass Filter

Well it's been hot here, with two days over 40degrees Celsius now. I've used that time incorporating a pre-driver into the radio and considering the harmonic issue. It turns out that in Australia there is no allocation of the spectrum where the second harmonic would be an immediate problem. With that in mind I have stopped worrying about the exciter harmonic level for now.

The existing 7 pole LPF can be rebuilt. I have settled on a 7 pole Chebyshev filter as follows:

The suggested attenuation of the second and third harmonics is 37dB and 67dB. I would like more attenuation of the second harmonic but I will wait and see what I achieve in practise before redesigning the filter. If I achieve my targeted 50dB below the carrier for the second harmonic that will be less than 1mW of RF power being radiated which should keep me out of trouble.

I have some 110pF surface mount RF caps which has shaped the filter I have selected. I only need remove the two 33pF outside capacitors on the filter, to be replaced by 110pF capacitors, and pad the inside capacitors with 110pF.

LPF Board before modification

This morning I quickly wound the inductors, measured them to ensure they were close and put everything back together. And I removed that disc ceramic capacitor shown in the photo above.

Regards
Richard VK6TT