Tunable Audio Notch Filter

RARE DX under QRM ? Dig it out with this filter between your receiver and extension speaker or headphones, BOOST your DX/QRM ratio, 40 dB notch, WINKLE out the WEAK DX from under tiring whistles and cw interference FAST - when interference starts just notch it out and carry on DXing. Set to 5kHz for hiss and splatter. Its built-in speaker amplifier maintains the gain and sharpens the notch so that the resulting "hole" has little effect on speech.


TYPICAL PERFORMANCE. Notch frequency range 350 - 5000 Hz, notch depth 40dB, 20dB bandwidth 150Hz at 1kHz, unity voltage gain, input resistance 10k ohms, output resistance 1 ohm, power output 0.1W (12V, 8 ohm load), supply needed 9-15V at 50mA, controls for tuning and notch/flat (bypassed when off), 4 x 7 x13 cm, 200 g.

"heterodyne disappeared completely", Practical Wireless.

"fully compares with other makes at much greater prices", HHA in Accrington.

"impressed at the ease with which I can tune out an annoying heterodyne", Practical Wireless.

"...it works 100%", JV in Aberdeenshire.

The kit includes ALL parts. case, screws, wire etc, the printed circuit is tinned, drilled fibre glass and the detailed assembly and operating instructions include a circuit diagram and description.