Low Pass Filters

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Page for discussion of the low pass filters in the Minima transceiver.

I used the following toroids:


Here is a sweep of my 15MHz LPF (which rolls off at too low a frequency):


and the 30MHz LPF with the three notch filters tuned to 20MHz:


I have since re-designed the 15M LPF to give a better flat response and sharper roll off, the design looks like this:


and the sweep of the new filter looks like this:


and it physically looks like this:


I have also since modified the 30MHz LPF to include 1 38MHz trap to suppress the LO when Minima is tuned to 18MHz band, as well as two traps as per design to suppress BFO at 20MHz. 38MHz trap has 2uH coil instead of 3uH coil as designed. Sweep of 30MHz LPF now looks like this: