Radio: it's not just a hobby, it's a way of life

Current Operating Frequency and Mode

CQ 474.5 kHz CW and alternately tuning 472 kHz - 475 kHz for signals.

630-meter low pass filter values from WA3ETD

– Posted in: 630 Meter Instructional Topics, 630 Meters

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.

Good luck!