Notes on the Wacom WP-641 BpBr Cavity
An article by Kevin Custer W3KKC
Measurements by Jim Labrecque KC1RM

The pass frequency is adjusted by rotating the black knob on the top.  The notch rods adjust the separation of frequency from the pass to the notch.  By moving the rods to their extremes... one can see what the minimum and maximum frequency separation is and the amount of notch depth obtainable at these extremes.  On a typical 600 kc. split the notch depth is around -38 at 600 kc. per individual cavity. As the frequency separation becomes less, the obtainable notch depth is also less.  On separations greater than 600 kc, the notch depths get somewhat greater.

Here is a test that was done on an 8" High Pass Low Reject (HPLR) BpBr cavity set to 150 MHz.

The minimum frequency separation obtainable is about 170 kHz.  Moving the rod any further out did not change the frequency.  At this frequency separation, the notch depth is about -18.5 dB from the pass.

Going the other way, the notch moves out about 8.77 MHz.  This is with the rod inserted fully.  At this frequency separation, the notch depth is about -43 dB from the pass.

What is interesting, is that if you open the span of the spectrum analyzer up to about 10 MHz, there are actually two (2) notches.  There is also a point where you adjust the tuning rod such that the notches are symmetical about the pass frequency.

With the rod adjusted so that the notches are symmetrical, notch depths of -40.7 dB were measured with a frequency separation of 2.4 MHz.

HTML Copyright 2000 Kevin Custer  W3KKC
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