Filter 144 MHz
The filter was tuned with NanoVNA. The attenuation is around 0.5 dB. Input and output impedance is 50 Ohm.
 The starting aluminium box. (https://www.gme.cz/hlinikova-prumyslova-krabicka-ip65-u-03-19) |
 Both sides were ground to a flat surface. The original gasket was replaced with a conductive one. |
 The drilling phase of the project.. |
 The finished filter with the top cover removed. |
 The detail of one side. The ceramic capacitor is 6.8 pF. The trimmer is roughly 1...6 pF. |
 The capacitive coupling must be carefully adjusted.. |
 The completely finished filter. |
Update:
After some time I began to be curious what the performance of my
filter actually is. I measured the professional tuned cavity
Rohde & Schwarz type HS to have some comparison:
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Obviously the shape of the curve differs, the cavity is more sharp. On the other my filter has a comparable or even higher attenuation at the stop band.
My filter, however, brings these advantages: