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Apidictor Filter Characteristics

The graph illustrated below was sent to me by Rex Boys. The image was traced over a scan of a photostat and thus may have errors of around plus or minus 1 pixel, but in the main any errors are likely to be less than 0.5 pixel as human judgment was used during the rather tedious tracing. I apologise to those users of low resolution monitors for the need to scroll across the images.

In creating this image I have left the plotted lines exactly as the original, including the wobbles. The schematic within the graph shows a combined signal generator and level meter coupled to Rex's own Apidictor unit. The actual test were conducted at the BBC (where both Rex and Eddie Woods worked).

There has been some confusion about switch positions and function in the past, but they should be:-
position 1 straight through, position 2 narrow band pass and position 3 high pass.
In reading Rex's "listen to the bees" There is a reference to the high pass filter for hiss detection being for frequencies above 3,000 Hz, but the curve shows a starting point at around 500 Hz, maybe this was just the result of simplifying the filter from the original breadboard model, but we can improve on this considerably. (Unless the figure quoted should have been 300 Hz.)
Apidictor filter charactreistic graph

The shape of the original graphs  has more to do with what could be achieved simply with the technology available, rather than the desired characteristic. Therefore I reproduce a simplification of the characteristic that may be more readily achieved by today's methods and is more appropriate to what is being listened for. The lines use the same colours as in the original and the original ones themselves are shown feint. Apidictor 'perfect' filter charactreistic


As I am a radio ham I have on my shelves several audio filters that are fully adjustable in terms of high pass, low pass, band pass and notch... By using several of them in sequence almost any filter characteristic can be set up. If I can get hold of audio tapes, CDs or audio files taken from different hives with known colony conditions I would be able to do some further work 'on the bench'.

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Written... 13 December 2001, New Domain 15 April 2004,

Electronics Favicon Coding Standard 2003 Issue 5