HOW TO USE OUR NOTCH FILTER BOARD

The frequency is set by the resistance across RF1 (TB2) and RF2 (TB7).  This may be a dual pot, or,  more likely, two fixed value resistors.  These values can be a little tricky to set, so two "trimmer" pots (RF1V and RF3V) are included which makes it considerably easier to set the notch frequency.

The depth of the notch is set by adjusting the amount of feedback as set by RF4 (TB8) and RF5 (TB9).  A very deep notch of around -65 to -70DB can be obtained but at the cost of signal "leakage" into the second harmonic.  In many cases this will not be be a problem, but when used to make a THD distortion meter the fundamental leakage may cause inaccurate readings.