Looking for a power-scalable low pass field for 630-meters? I’ve received a lot of questions about low pass filters in the last few days.
Try these values for a 5-pole Chebyshev filter with 50 ohms in and out (DC blocked configuration) from John Molnar, WA3ETD / WG2XKA:
C1 .01 uF
L1 14.5 uH
C2 .016 uF
L2 14.5 uH
C3 .01 uF
Type-2 iron powder ferrite works well. Scale the cores for power levels. You can use this calculator to determine the number of turns needed.
Capacitors should be pulse-rated WIMA’s or silver mica transmitting varieties. Mix and match values to achieve C2 value. Lowest available tolerances are best but I don’t fear 5% capacitors. I prefer higher voltages on caps than are necessary. A 100W PA is about 100V peak into 50 ohms. I, personally, would still use a 500V silver mica capacitor. Doing so enhances long term survivability because the capacitors are really abused in low pass filters.