ONAIR, 1500 W FM Low Pass Filter

This very heavy duty 50 MHz Low Pass Filter was constructed by using a pair of 50 pF, 15 kVDC ceramic doorknob capacitors, and three air wound self-supporting coils.  

The center coil ( L2 ) is 6 turns,  2.5" long, using #6 AWG copper wire wound on a 7/8" diameter form.  Input and Output coils ( L1 and L3 ) are each 4 turns, 2'' long, using  #6 AWG copper wire wound on a 3/4" diameter form.   The enclosure was built to fit the space required for the coils.  The box is 12" long,  4" wide and 4.5" high.  Baffles were mounted around each capacitor to prevent enclosure resonance at UHF harmonics.  7/16 DIN connectors were used on both ends.

Insertion loss was measured at less than .06 dB, with attenuation greater than 24 dB at 100 MHz