Vectronics VEC-830K Super SSB Audio Filter Ham Radio Homebrew Kit Ideal for Contesting, DXing, and ragchewing Plugs into phone jack of your receiver or transceiver to drive head phones. Also connects between audio stages for speaker operation. Knock out undesired audio with 8 poles of active IC filtering. Includes highpass cutoff at 375Hz plus switch selectable lowpass cutoffs at 2.5, 2, 1.5 KHz (36dB per octave rolloff)